The extended phenotype: genetics beyond the body

Genes determine our eye color, height, development throughout life and even our behavior. All living beings have a set of genes that, when expressed, manifest themselves in a more or less explicit way in their body, modeling it and giving it a wide diversity of traits and functions. However, is it possible that the expression of some genes has effects beyond the body itself?

Discover some basic ideas about the extended phenotype theory.

First of all, let’s talk about two basic, but not less important, concepts that will help you to understand the extended phenotype theory: genotype and phenotype.

Genotype

Genotype is the collection of genes or the genetic information that a particular organism possesses in the form of DNA. It can also refer to the two alleles of a gene (or alternative forms of a gene) inherited by an organism from its parents, one per parent.

The genetic information that a particular organism possesses in the form of DNA constitutes its genotype. Public domain image.

It should not be confused with the genome: the genome is the set of genes conforming the DNA that a species has without considering its diversity (polymorphisms) among individuals, whereas the genotype does contemplate these variations. For example: the human genome (of the whole species Homo sapiens sapiens) and the genotype of a single person (the collection or set of genes and their variations in an individual).

Phenotype

The genotype, or at least a part of it, expresses inside an organism thus contributing to its observable traits. This expression takes place when the information encoded in the DNA traduces to synthetize proteins or RNA molecules, the precursor to proteins. The set of observable traits expressed in an organism through the expression of its genotype is called phenotype.

Eye color (phenotype) is determined by the expression of a set of genes within an organism (genotype). Picture by cocoparisienne on Pixabay (public domain).

However, genes are not always everything when defining the characteristics of an organism: the environment can also influence its expression. Thus, a more complete definition of phenotype would be the set of attributes that are manifested in an organism as the sum of its genes and the environmental pressures. Some genes only express a specific phenotype given certain environmental conditions.

The extended phenotype theory

The concept of extended phenotype was coined by Richard Dawkins in his book “The Extended Phenotype” (1982). Dawkins became famous after the publication of what would be his most controversial work, “The Selfish Gene” (1976), which was a precursor to his theory of the extended phenotype.

In the words of Dawkins himself, an extended phenotype is one that is not limited to the individual body in which a gene is housed; that is, it includes “all the effects that a gene causes on the world.” Thus, a gene can influence the environment in which an organism lives through the behavior of that organism.

Dawkins also considers that a phenotype that goes beyond the organism itself could influence the behavior of other organisms around it, thus benefiting all of them or only one… and not necessarily the organism that expresses the phenotype. This would lead to strange a priori scenarios such as, for example, that the phenotype of an organism was advantageous for a parasite which afflicts it rather than for itself. This idea is summed up in what Dawkins calls the ‘Central Theorem of the Extended Phenotype’: ‘An animal’s behaviour tends to maximize the survival of the genes ‘for’ that behaviour, whether or not those genes happen to be in the body of the particular animal performing it’.

A complex idea, isn’t it? However, it makes sense if we take into account the basic premise from which Dawkins starts, which addresses in his work ‘The selfish gene’: the basic units of evolution and the only elements on which natural selection acts, beyond individuals and populations, are genes. So, organisms’ bodies are mere ‘survival machines’ improved to ensure the perpetuation of genes.

Examples of extended phenotype

Perhaps all these concepts seem very complicated, but you will understand them better with some examples. According to Dawkins, there exist three main types of extended phenotype.

1) Animal architecture

Beavers build dams and modify their surroundings, in the same way that a termite colony builds a termite mound and alters the land as part of their way of life.

Dam built by beavers. Picture by Hugo.arg (CC 4.0)

Termite mounds in Autralia. Public domain image.

On the other hand, protective cases that caddisflies build around them from material available in the environment improve their survival.

Caddisfly larva inside its protective case made up of vegetal material. Picture by Matt Reinbold (CC 2.0)

These are all examples of the simplest type of extended phenotype: the animal architecture. The phenotype is, in this case, a physical or material expression of the animal’s behavior that improves the survival of the genes that express this behavior.

2) Parasite manipulation of host behavior

In this type of extended phenotype, the parasite expresses genes that control the behavior of its host. In other words, the parasite genotype manipulates the phenotype (in this case, the behavior) of the host.

A classic example is that of crickets being controlled by nematomorphs or gordiaceae, a group of parasitoid ‘worms’ commonly known as hair worms, as explained in this video:

To sum up: larvae of hair worms develop inside aquatic hosts, such as larvae of mayflies. Once mayflies undergoe metamorphosis and reach adulthood, they fly to dry land, where they die; and it is at this point that crickets enter the scene: an adult cricket feeds on the remains of mayflies and acquires the hair worm larvae, which develop inside the cricket by feeding on its body fat. Adult worms must return to the aquatic environment to complete their life cycle, so they will control the cricket’s brain to ‘force’ it to find a water source and drop in. Once in the water, the worms leave the body of the cricket behind, which drowns.

Other examples: female mosquitoes carrying the protozoan that causes malaria (Plasmodium), which makes female mosquitoes (Anopheles) to feel more attracted to human breath than uninfected ones, and gall induced by several insects on different host plants, such as cynipids (microwasps).

3) Action at a distance

A recurring example of this type of extended phenotype is the manipulation of the host’s behavior by cuckoo chicks (group of birds of the Cuculidae family). Many species of cuckoo, such as the common cuckoo (Cuculus canorus), lay their eggs in the nests of other birds for them to raise in their place; also, cuckoo chicks beat off the competition by getting rid of the eggs of the other species.

Look how the cuckoo chick gets rid of the eggs of reed warbler (Acrocephalus scirpaceus)!

In this case of parasitism, the chick is not physically associated with the host but, nevertheless, influences the expression of its behavioral phenotype.

Reed warbler feeding a common cuckoo chick. Picture by Per Harald Olsen (CC 3.0).

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There are more examples and studies about this concept. If you are very interested in the subject, I strongly recommend you to read ‘The selfish gene’ (always critical and from an open minded perspective). Furthermore, if you have good notions of biology, I encourage you to read ‘The extended phenotype’.

Main picture: Alandmanson/Wikimedia Commons (CC BY-SA 4.0)

Insects and microorganisms symbiosis: the endosymbionts

Symbiotic relationships are an important motor for organisms’ diversification and evolution. The relationships insects have established with some endosymbiotic microorganisms (that is, those inhabiting the inner of their bodies) have provided them of a lot of surprising physiological and ecological adaptations. 

The value of the relationship between insects and their endosymbionts

The major cause for insects’ evolutive and adaptive success is their potential to stablish beneficial relationships with other life beings and, especially, with those microorganisms inhabiting their insides: the endosymbionts.

Some years ago, it was considered that the greatest contribution of endosymbiotic microorganisms to the physiology of insects was their role in feeding habits, which would explain, at least in part, the diversity of diets among insects. However, it has been shown that endosymbionts affect many other physiological traits.

Types of endosymbiosis in insects

Endosymbiotic microorganisms can be found inside the gut, in the spaces between cells and inside cells.

Generally, the more internal the endosymbiotic microorganisms are within the host’s body, the closer their relationship with the insect is. The four most common types of endosymbiosis in insects are explained below, from the most external and least close relationship to the most internal and closest one.

Gut microbes

Gut microbiota of insects is composed both of prokaryotes (unicellular, without nucleus, like bacteria and archaea) and eukaryotes (unicellular or pluricellular, with nucleus, like protozoans) that live outside the gut cells. They usually inhabit the hind part of insect’s gut (hindgut), either moving freely in its lumen or remaining attached to its walls. In some phytophagous insects, likes termites and cockroaches, the hindgut is a chamber without oxygen (anaerobic) where fermentation of cellulose and other complex sugars takes place.

 

Worker termite gut; the green part corresponds to the hindgut without oxygen. Figure belonging to the following paper: Brune, A. (2014). Symbiotic digestion of lignocellulose in termite guts. Nature Reviews Microbiology, 12(3), 168-180.

In termites, this anaerobic chamber contains facultative anaerobic prokaryotes (they can develop either with or without oxygen) and obligate anaerobic prokaryotes (they can only develop without oxygen), such as spirochetes and methanogens, which aid in digestion. In addition, in some worker termites, this chamber also contains protozoans that play a major role in the digestion of wood cellulose (Have you ever seen a piece of furniture pierced by termites?).

Unlike other endosymbionts, gut microbes are horizontally transmitted between insects; that is, insects don’t inherit gut microbes from their parents, but they should acquire them throughout their lives. In termites, acquisition of gut microbes takes place through a process called trophallaxis: the workers, which are the only able to feed by themselves, digest the food and transmit the resulting product mixed with gut microorganisms to the rest of the colony members through their mouthparts.

Trophollaxis. Picture by Shutterstock.

Moreover, microorganisms are removed during molting processes, so termites (and other insects performing trophollaxis) can acquire them again through trophollaxis.

Endoparasites

Parasites that live and/or develop inside an organism are known as endoparasites. They are also horizontally transmitted between insects.

Insects stablish fairly more relationships with pluricellular endoparasites than with microorganisms, being the pluricellular endoparasites the most harmful for insects in general terms; these are the cases of insect parasitoids (of which we talked in this post) and nematodes (able to transmit deathful bacteria to insects).

The most relevant endoparasitic relationship between insects and microorganisms, and the only one we are going to explain here, are vectors: the insect (or vector) serve as a container to the parasite until it reaches the definitive host. Parasites transported by vector usually are pathogenic protozoans harmful to vertebrates, like Trypanosoma (Chagas disease), Leishmania (leishmaniosis) or Plasmodium (Malaria).

Mosquito of the genus Anopheles, the major vector of the protozoan causing malaria worldwide: Plasmodium. Public domain image.

Extracellular and intracellular symbiosis

Unlike gut microbes and endoparasites, extracellular and intracellular endosymbionts are vertically transmitted generation after generation; that is, the insect inherits them from its parents

• Extracellular endosymbionts
  

Extracellular endosymbionts, which can be both prokaryotes and eukaryotes, can be found in different organs of the body (even in the intestine along with the gut microbes). In any case, they never penetrate inside the cells. However, some species can be found outside and inside cells.

Since many extracellular microorganisms can also be intracellular, the possibility that they are found, in an evolutionary sense, in a transition stage between gut microbes and intracellular endosymbionts has been discussed.

An interesting case of extracellular endosymbiosis takes place in some species of aphids of the tribe Cerataphidini. Generally, aphids stablish a close relationship with an intracellular endosymbiont bacteria (Buchnera), but in some species of the aforementioned tribe these bacteria are substituted by extracellular unicellular yeast-like fungi (YLS or ‘yeast-like symbiont’) which inhabit the cavities between organs and inside different adipose bodies. Like Buchnera in the rest of aphids, YLS would play a key role on aphid feeding habits, participating in the production of essential nutrients.

Ceratovacuna nekoashi (Cerataphidini). Link (CC 2.5)

It is suggested that YLS would have evolved from an entomopathogenic fungus (that is, harmful to insects) whose lineage would later have derived into beneficial endosymbiotic organisms.

• Intracellular endosymbionts
  

It is considered that at least 70% of insects has endosymbiotic microorganisms inside its cells. There exist two types of intracellular endosymbionts:

Mycetocyte symbionts or Blochmann bodies

Bacteriocytes or mycetocytes are specialized adipose cells containing endosymbionts which can be found in some groups of insects. These cells are vertically transmitted to the offspring and gathered together forming organs known as mycetomes o bacteriomes.

Blochmann bodies, or simply the endosymbionts inside mycetomes, are related to three groups of insects: Blattaria (cockroaches), some groups of heteropterans within Homoptera (cicadas, rust flies, aphids, etc.) and Curculionidae (curculionid beetles).

Buchnera aphidicola inside a mycetome of the aphid Acyrthosiphon pisum. The central element is the mycetome’s nucleus. Buchnera cells, which are round, are located packed in the citoplasm of the mycetome. Picture by J. White y N. Moran, University of Arizona (CC 2.5).

The most well studied case is the relationship between Buchnera and aphids. This intracellular bacterium recycles the uric acid and some other nitrogenous wastes produced by the aphid in order to produce the amino acid glutamine, which is then used by this same endosymbiont to produce other essential amino acids necessary for the aphid to develop. It is also considered that Buchnera produces vitamin B2 (riboflavin). This can explain why aphids have such a high reproductive rate and a big evolutive success despite having a diet rich in carbohydrates (which they obtain from plant’s sap) and poor in nitrogenous compounds.

It has been confirmed that Buchnera cells decrease in number when nutrients are scarce. This suggests that aphids use Buchnera cells as an alternative food source in difficult situations. So, aphids take more advantages from this relationship than Buchnera.

Guest endosymbionts

In this case, the guest (endosymbiont) alters some physiological traits of the insect to obtain some advantage.

Guest endosymbionts usually affect the sex ratio of insects (proportion of males and females in a population) as well as other reproductive traits. Guest endosymbionts that alter the sex ratio are known as sex-ratio distorters. Some guest microbes inhabiting the cytoplasm of insect’s cells are vertically transmitted to the offspring through ovules, so they need a higher proportion of female insects to guarantee their own perpetuity. To alter this proportion, they use different methods: male killing, induction of parthenogenesis, feminization or cytoplasm incompatibility, for which they usually induce changes at the genetic level.

One of the most well-studied cases is Wolbachia, an intracellular bacterium capable to induce a sex-ratio bias through almost every of the aforementioned methods.

Phenotypes resulting from insects infected with Wolbachia. Figure belonging to the following paper: Werren, J. H., Baldo, L. & Clark, M. E. 2008. Wolbachia: master manipulators of invertebrate biology. Nature Reviews Microbiology, 6(10), 741-751.

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Do you know any other relationship between microbes and insects? Leave your comments below!

References

• Bourtzis K.,  Miller T. A. (2003). Insect Symbiosis. CRC Press.
• Douglas, A.E. (1998). Nutritional interactions in insect-microbial symbioses: Aphids and their symbiotic bacteria Buchnera. Annual Review of Entomology, 43: 17–38.
• Vega F.E., Blackwell M. (2005). Insect-Fungal Associations: Ecology and Evolution. Oxford University Press, USA.

The cover image is a montage made by the author from two images: 1) bacterium vector (by Flaticon from www.flaticon.com) and 2) termite vector (obtained from www.allstatepest.com.au).

The mom’s microbiological present

During the gestation, the mothers bring all that necessary for thecorrect development of the baby. Did you know that also implies to microorganisms? For the good maturation of our intestines and immune system, we  need a contribution microbiological from mom. Enter and discover the different bacterial species  that gives us our mother in our first days of life.

STERILE PREGNACY?

For a long time it was believed that the uterus and amniotic sac that containing the fetus are a sterile place without any microbiological presence. Moreover, the mere presence of microorganisms was associated with a disease or a risk to the baby. So, it was believed that the fetus was conducted in a completely sterile environment during 40 weeks of gestation and came into first contact with some type of bacteria during birth.

Today, thanks to technological advances and genetic studies, it has been observed that this dogma was not true. Fetuses are in contact with bacteria throughout gestation. Generally it is non-pathogenic bacteria that are transmitted by the mother during pregnancy and after delivery.

Ultrasound of the placenta. In red are the bacterial communities, while in blue are observed them veins. (Image of Wolfgang Moroder)

This maternal microbiological transmission is a widespread phenomenon in many groups of the animal kingdom, such as Porifera, mollusks, arthropods and chordates. The presence of this phenomenon throughout the animal kingdom and the ease with which these organisms to reach the fetus, show that this transmission is a very old process and represents an evolutionary advantage to organisms.

Different organisms that maternal transmission has been observed. A) Pea Aphid (Acyrothosiphon pisum). b) Common chicken (Gallus gallus domesticus). c) Red Salmon (Oncorhynchus nerka) and d) River turtle Podocnemis expansa. (Image: Lisa Funkhouser).

TRANSMISSION ROUTES

There are different ways why does the mother get the baby the first bacterial communities. So the baby’s contact with his future microbiome is given for the first time through bacteria of the placenta. Then and during the delivery, some bacterial strains are transferred through the birth canal, skin and finally, through breast milk.

The differents transmission routes of microbiological communities. (Image: Lisa Funkhouser)

MICROBIOME OF THE PLACENTA

Is relatively recently,  that the presence of bacterial communities in this organ is known. Yet it is noteworthy that it is a small microbiome in terms of abundance. Generally, it is non-pathogenic microorganisms, but their variation could be related to common disorders in pregnancy such as premature births.

Initially it was believed that these bacterial communities would be related to the vaginal microbiota of the mother, but it has been observed that placental bacteria are more similar to those of the mother oral microbiota. According to research, the bacteria come from the mouth of the mother to the fetus through the bloodstream. So good oral health is essential for the proper development of the baby.

In the following diagram represent the main bacterial species identified in the human placenta. 

The major bacterial phyla observed in the placenta. Own image.

TRANSMISSION DURING CHILDBIRTH

As it is well known, during labor, a major transfer of bacteria occurs. Most of these bacteria are related to the vaginal and fecal microbiota of progenitor. During pregnancy, the vaginal microbiome of the mother varies and becomes less diverse, being more predominant the presence of bacteria such as Lactobacillus sp.

Still, it is noteworthy that this transmission will vary depending on the type of delivery, that is, babies born vaginally present similar microbiome to that of the vagina of the mother microbiota (Very rich in Lactobacillus sp., Prevotella sp., Bacteroides and Bifidobacterium sp.), while those born by Caesarean section present a more similar microbiome to the microbiota of breast skin, rich in Clostridium sp., Staphylococcus sp., Propionibacterium sp. and Corynebacterium sp.

The first baby’s microbiome depends on the type of chilbirth. In this diagram we can observe the differents bacterial communities that are involved in each one. (Own image)

SKIN CONTACT

As in other cases, skin with skin contact produces a transmission of microorganisms between two humans. In this case, it can be through the type of delivery (C-section), by contact with the external vulvar area of mother and by contact with the outer skin of his mother.

Some of the bacteria that are acquired at birth and are commonly in the skin of adult humans are Staphylococcus sp. Corynebacterium sp. and Propionibacterium sp.

MILK WITH BACTERIA

Another of the myths about esteril pregnancy was breast milk. Until recently it was thought that breast milk was sterile and bacteria that were in the samples were due to cross-contamination through the skin of the mother and the baby’s mouth. Today, thanks to the discovery of certain anaerobic bacteria, has concluded that the mother also provides certain bacterial communities by human milk.

There are a variety of microorganisms in milk and generally vary depending on the type of feeding and origin of the mother (See the different abundances of microorganisms in different mothers in the figure below). Still, it has been observed that during the early months of breastfeeding, breast milk is rich in Staphylococcus sp., Streptococcus sp. and Lactococcus sp.; while from six months of lactation milk is rich in typical microorganisms of the oral microbiota as Veillonella sp., Leptotrichia sp. and Prevotella sp.

Differences in the abundance of the bacterial species found in the breast milk of 16 analyzed subjects. (Image: Katherin Hunt)

Thus, it is expected that breastfed infants present a different intestinal and fecal microbiota than the artificialfed babys. These bacteria favor the baby against diarrhea, respiratory diseases and reduce the risk of obesity. BE CAREFULL! This does not mean that a child fed with artificial milk is worse than a breastfed, as many of these bacteria also can be purchased by other means.

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All these bacterial transmissions by the mother let the baby start the maturation of their immune system and the development of good intestinal microbiota. Our mothers always give it best to us!

REFERENCES

• Hunt, Katherin. Characterization of the diversity and temporal stability of bacterial Communities in human milk. (Article in English)

• Grens, Kerry. The maternal Microbiome. (Article in English)

• Funkhouser, Lisa. Mom knows best: the universality of maternal microbial transmission. (Article in English)

• Cover image: Joanna Noguera Riobueno.

Basic microbiology (II):thousands of bacterial forms

Imagine a bacterium. What image has come to your mind? You have possibly thought of elongated like a Bacillus, type E. coli bacteria or into a small ball. For years, we have associated the bacterial morphology to a few basic shapes, but there are a multitude of forms in the environment. Discover them in the second chapter of Basic Microbiology!

BACTERIAL SHAPES

Microorganisms represent a very varied group of organisms invisible to the naked eye. In the previous chapter previous chapter of this article collection we talk about the microbe’s size and in this second chapter of basic microbiology we are going to talk about the different morphologies or forms that exist of the group bacteria and the archaea group (extremophile bacteria).

Usually, when we started the trip in the bacterial world, found that bacteria have a series of basic shapes: coccus (spherical or berry), bacillus (shaped) and spirillum (coiled), as well as its aggregations. These are formed by the union of the cells after division. For example, there are species that are pairs of cocci (known as diplococci), others form long chains of cocci (such as Streptococcus sp.), others are arranged in three-dimensional cubic groupings (like Sarcina sp.) and others formed structures like clusters of grapes (Staphylococcus sp.).

Cocci and its aggregations (Image: Aula virtual).

In the case of rod-shaped bacteria, we can find also different groups such as the diplobacillus or the streptobacillus (such as for example Bacillus cereus). Apart we can find many variations of bacillus: there are shorter and more rounded (numerous coccobacillus, as it would be the case of Yersinia pestis), there are Pleomorphic (who have one or more forms depending on the phase of the cell cycle), finished in tip (as for example Epulopiscium fishelsoni), curved or crooked.

Rod shaped bacteria and its aggregation (image: Aula Virtual)

 

Finally, the spiral shapes appear as it would be the case of the vibrios (in the form of comma, as Vibrio cholerae), the spirils (as Rhodospirillium rubrum) or spirochaetes (Spirochaeta stenostrepta).

Spiral bacteria (Image: Aula Virtual).

 

But why morphology is generalized to these forms?

Should be remember that it microbiology always had been a medical discipline and these forms are the more recurrent in the pathogenic bacteria. Now, with the rise of Microbiology, it has been observed that in the environment there is a huge variety of different morphologies, some much more complex that is known so far. The following graphic is result of an elaborate study of David T. Kysela and shows the true morphological variety that exists in the bacterial world.

Differents bacterial morphologies around the Philogenetic tree (Image: David T. Kysela)

FEW EXAMPLES

Some individual bacteria present peculiar structures, as for example stretching narrow known as prostheca. This would be the case of Caulobacter sp. and Hyphomicrobium sp. These stretching allow to anchor the bacterium to a solid surface. There are bacteria that can also present stems, spines, or tips.

Hyphomicrobium sp. with their prostheca (Image: Holm Niels)

Other bacteria have unusual shapes. For example, Halophyte bacteria (that support high levels of salt concentration) like Stella sp. and Haloquadratum sp. Form a very odd aggregation. The first has a star shape and second rectangular shape.

Diagram of the characteristic shape of Stella vacuolata (a) and Haloquadratum walsbyi (b). (Image: Aula virtual).

Haloarcula japonica is an individual halophyte bacteria as the previous ones, presenting a very striking morphology. As we can see in the first section of the image, in certain stages of the cell cycle has a triangular shape. On the other hand, Pyrodictium abyssi (b) presents one of the most striking morphologies, since it has the form of a  “y”letter.

a) Haloarcula japonica (Image: Nite) b) Pyrodictium abyssi (Image: Benjamin Cummings)

Also, there are very characteristics bacterial associations, as for example long chains of organisms that give an aspect of filamentous bacteria. This is the case of the bacterial phylum known as Chloroflexi, where green sulfur bacteria like Chloroflexus sp. are classified (b). Another very striking grouping are the palisades. These are characterized by bacterial rods with vertical connections. A well-known example is the case of Simonsiella muelleri (b).

a) Microphotography of Chloroflexus sp. (Image: JGI Genome Portal). b) Scanner microphotography of Simonsiella sp. (Image: J. Pangborn)

In some cases, there are bacteria that do not have a definite shape or this may vary throughout the cell cycle. In this case, we speak of technically known as Pleomorphic bacteria. Corynebacterium sp. and Rhizobium sp. are good examples of this type of morphology.

DETERMINED BY THE GENOME

The form or morphology that presents the different bacteria is determined by its genome. This fact, and the great diversity of morphologies in different environments, suggest that this feature has an adaptive value and that have been produced by selective forces.

In general, the morphological features are attributed to environmental events as for example the limitation of nutrients, reproduction, dispersion, evasion of a predator or detection of the guest. In the case of filamentous bacteria, they presented a better buoyancy in liquid media and are more difficult to digest by protists. Helical bacteria move easiest in viscous media, while a spherical bacterium or cocci is ideal for the diffusion of nutrients (because it increases the surface/volume ratio).

So, expect that same morphology may appear by convergence in different lineages (that do not have a common ancestor), i.e. that shape is an adaptation to a given environment. For example, before, bacteria that have prostheca were grouped into a single genre known as Prosthecomicrobium, but thanks to genetic studies, this genus has been divided in three different genres. The surprise came when noted that each one of these genera was more similar to a gender without prostheca that between them, i.e., not were related phylogenetically. Simply these species have developed the same system of adaptation to the environment.

However, there are also remember that there are morphological characteristics that are inherited from a common ancestor and are preserved because it is useful for the life of the microbe.

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As well as increase the knowledge in the microbial world and genetic techniques, we will discover more facts about these tiny organisms.

REFERENCES

• Brock, microbe Biology. Madigan. Ed. Pearson.
• Microbiology Introduction. Tortora. Ed. Panamericana. (Free access in spanish here)
• David, T. Kysela. Diversity takes shape: understanding the mechanistic and adaptative basis of bacterial morphology. PLOS Biology. (Free access)
• Kevin D. Young. The Selective Value of Bacterial Shape. Microbiology and Molecular Biology Reviews. (Free access)
• Kevin D. Young. Bacterial morphology: why have different shapes? Current Opinion in Microbiology. (Free access)
• Cover Photo: Escuela y Ciencia.

  

Why did change the water colour?

In August of 2016, the news of a green pool at the Olympic Games in Riode Janeiro was published in all media. Everyone was shocked and spokeon the topic, but this phenomenon occurs in nature more often than wethink, for example in  lake Urmia (Iran), lake Clicos (Lanzarote), Lake Hilier (Australia), etc. Would you like to know the reason for these changes?

THE CONCEPT OF EUTROPHICATION

We have heard speak so much about the surprising pool’s colour change of them Games Olympic, but do you know the scientific explanation to this effect?

The Rio 2016 Olympic Games pool. The color change was apparent and caused by the proliferation of microscopic algae. (Image: Verne. El País).

This phenomenon of change of color  is very common in the nature. It is the eutrophication of  water. This concept makes reference to the proliferation of organisms due to an increase in the concentration of nutrients in water. So understand it easily: an increase of food occurs in water and  resulting in a rise in organisms which modify the characteristics of the water such as color, turbulence, etc.

In water bodies like lakes or swimming pools, this phenomenon is more commonly, but in sea also appear this blooms of organisms (above all phytoplacton).

Example of eutrophication by algae in a lake. (Image: Radio wtcv)

The main nutrients that influence the eutrophication of lakes are the limiting factors nitrogen and phosphorus. In bodies of sweet water this last is determinant, while in salted water the nitrogen tends to be the limiting factor. A increase of these nutrient’s concentrations  begins the process of eutrophication and proliferation of photosintetic organisms (mostly microalgae and  photosynthetic bacteria as cyanobacteria or archaebacteria as the Holobacterias).

When a lake receive excessive nutrients, all the trophic structure  can change very quickly. Water is too fertilized and photosynthetic organisms proliferate causing an algae or microorganisms bloom.

Basic diagram of eutrophication (Image: Sachink Biology)

Normally, we speak of  microalgae (phytoplankton) and cyanobacteria blooms, but in certain cases, when the change of nutrients is more drastic (that affects to the composition or chemical characteristics of  water) we can speak of the proliferation of bacteria and Archaea. For example in lake Urmia (Iran), proliferate exponentially the Halobacteria that support large saline concentrations. Due to the low rainfall and continuous extraction ofwater for agriculture, water becomes more salty and impede the life of the majority of organisms and favouring the blooms of the more specialized, as Halobacteria. The red pigmentation arises by the presence of a pigment known as bacteriorhodopsin.

Satellite image of lake Urmia (Iran). The change of color is produced by proliferation of bacteria of the family Halobacteriaceae. (Image: La Vanguardia)

The example of Rio’s pool shows the initial stages  of algae bloom. Some lakes, however, are in more advanced stages of eutrophication, as it would be the case of the Clicos Lake in Lanzarote. In this Lake proliferate exponentially the  Ruppia maritima algae.

Photograph of the Clicos Lake in Lanzarote. (Image: National Geographic)

NATURALANDANTHROPOGENIC EUTROPHICATION

Natural eutrophication process is highly regulated, since it tends to a balance between the inputs (precipitation, runoff, erosion…) and outputs of nutrients. There are three trophic states trophic in lakes: the oligotrophic, the mesotrophic and the eutrophic, depending on certain characteristics of water such as the concentration of nutrients and oxygen, its turbulence, the primary production etc. These states marke ‘age’ of lakes, i.e., a young lake will be oligrotrophic while one older will tend to eutrophication.In the following table we find some differences between these threetrophic states:

Table with some differences between the different trophic states.

The ecosystems natural present resilience, i.e., capacity to return to the normal state after a sudden disturbance. Even so, with time, the ancient lakes tend to accumulate sediments and organic remains,making finally the Lake in a swamp. This process can last thousands of years.

The anthropogenic eutrophication makes reference to one type of eutrophication caused by humans. Waste water, waters rich in fertilizers and other types of pollution are the main causes of this type of eutrophication. The ecosystem is not capable of eliminating as many nutrients in a balanced way and they tend to accumulate. In this case, the process lasts much less that the natural: as only some decades are sufficient.

Comparison between the two types of eutrophication. (Image: New Brunswick, Canadá).

THE BEGINNING OF THE END

The eutrophication, however, mark the beginning of the death of ecosystem. But, how?

The increase in nutrient concentrations produces an increase in the proliferation of aquatic plants and algae carried out photosynthesis. Therefore an organism bloom occurs and causes the formation of a barrier in the water. In the surface, the concentration of oxygen is maintained while in deep areas, where the light not penetrates with ease, is produces an increase of aerobic breathing  and decreases the photosynthesis. This process of oxigen consumption  causes that every time has less concentration of this gas and the medium is again anoxic.With enough oxygen, species before peacefully living in the Lake, now will disappear.

In the diagram you can see the barrier created by the proliferation of algae, leaving the deeper areas in a dark environment without oxygen. (Modified image from SPE International)

On the other hand, a high biological activity  implies a decrease of the dissolution of certain nutrients in the water, causing a change in the pH and salinity of this, conditioning seriously also the habitability of these waters and favoring the proliferation of extremophiles. In addition, the presence of certain algae suppose  the production of toxins that affect negatively to the lake’s native populations  The main toxic cyanobacteria that tend to proliferate easily are Anabaena sp, Cylindrospermopsis sp., Microcystis sp. and Oscillatoria sp. This implies a great loss in the diversity of the area.

Comparison of diversity in a oligotrophic lake and eutrophic one. (Image: Madrid+d)

Finally, the organic remains of dead organisms accumulate at thebottom of thelake, thus increasing the sediment layer. By time, the volume of water has been reduced significantly,turning the place into a swamp.

·

As in the majority of cases, the actions of the man have serious consequences in the environment. We must avoid the pollution or will lose the great diversity that surrounds us.

REFERENCES

• Eutrofización. Nestor Mazzeo. (PDF, spanish)
• Personal notes, Biology degree at UIB.

• Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems. Michael Chislock. Available  here .

• Cover photo: Axena.

 

Home’s micro-squatters

If you ever thought to be alone in your house, you were wrong. In your home there are thousands and thousands of micro-organisms sprout at ease. They are responsible for odors and pollution from yourhome. Would you like to know more about your tenants?

MICRO-SQUATTERS OF OUR HOUSES

It is stimated that about 90% if our time is spended in closed places, such as office, school or home. These places, as well as the rest of our planet, presents a environmental conditions suitable for proliferation of bacteria, fungi and arthropods. These communities are known as the Home’s Microbiome.

Photomicrograph of the bristle of a used toothbrush where proliferate a lot of microbial communities (Image: Science photo library)

The relations that we stablish with these communities of microorganisms can condition directly in our health. Can find beneficial microorganisms, indifferent microorganisms (i.e that do not produce any effect) and pathogenic microorganism (as Staphylococcus auereus resistant to antibiotics) or allergens as them mites. These pathogens, in most of cases, just represent a litle percentage and not pose any risk for them home’s occupants.

BACTERIA

Bacterial communities are very abundant in our homes. We can find them in every corner and have a great diversity. For example, in the dust is estimated that there are som 7000 different bacterial species. In the following graphic, can observe the broad diversity of bacterial species that colonizes certain regions of our home, such as the toilet’s lid, kitchen or our own beds.

Differents bacterial families that we can found arround our home (Image: G.E. Flores)

FUNGI

In normal conditions, a house can present up to 2000 different types from fungi. We can also find them in all home environment such as food, kitchen, walls and even in forgotten places during cleaning as for example the dust accumulated on the door frames. Among them, we can highlight the presence of Aspergillus, Penicillium and Fusarium (common envirnmental fungi). Also proliferate fungi responsible of the wood degradation (as for example Stereum, Tremetes, or Tremellosa) or fungi related with humans, like Candida.

Wall mold that appear in homes (Image: Mycleaningproduct.com) or fruit mold by Penicillium sp. (image: wisegeek).

MITES

These microorganisms represents to the Arthropods of our homes. Normally they live in dust, on rough surfaces such as fabrics, mattresses and pillowsa where they feed on died human and animals skin. We can find Dermatophagoides pteronyssus and Dermatophagoides farinae species, commonly knwon as dust mites. Even so, and to a lesser extent, we can find also some that another exemplay of Demodex folliculorum. This mite live in the hair follicles of our face and feeds on dead skin. Normally follows from the skin while we are sleeping.

Dust mite D. pteronyssinus (image: Göran Malmberg) and follicles mite Demodex folliculorum (Image: BBC)

BIOGEOGRAPHY AND  EMISSION SOURCES

The geographical distribution of these microscopic communities and those factors that determine it, are little known. For that reason, along this decade, studies about hom’s microbiome have increased and proliferated singnicantly.

The large microbial diversity changes over different locations in our home, i.e. we will not find the same microorganisms in bed than in the bowl of the toilet. For example, in our kitchen, depending on the place that we examine, we find greater abundance of specific bacterium or other. In the image bottom, us show as in the stove of our kitchen find more Salmonella sp than Clostridium sp.

Differences in the abundance of bacteria depending on the location (Image: G.E. Flores)

Even so, we can found a certain pater in this distribution, i.e. the microorganisms that inhabit certain areas are more similar than the comminities that we found in other locations. In the following dendogram we can observe that microorganisms found in our pillowcase are very similar to those that found in toilet, but completely different from whichwe can find in our kitchen cutting board.

Dendrogram of similarity between the bacterial communities of various areas of our home. (Image: Robert, D. Dunn).

But, what is the reason for this geographical distribution?

The response is found in the differents emission sources of these organisms. Depending on the source we can find find a few species or others. Obviously the main microorganism source of emission  into the environment are humans. We know that millions of bacteria and other microorganisms live in our body and they spread everywhere, either by respiratory activity, waste digestion or skin contact. Each human leaves a specific microbial fingerprint in those places. 

Major sources of emissions according to the area of the home to examine. See is that the largest source of emission are the own human. (Image: G. E. Flores)

In the graphic you can see that in some places appear microorganisms related to our intestines, specifically those who are ejecting with droppings. Is not wash you hans after going to the service, surely yo go spreading faecal bacteria everywhere. Also, if you pull the string with the toiled lid open, it causes the expansion of faecal bacteria as if it were a spray, reaching our toothbrushes  or the hand soap.

On the other hand, microbial diversity is very influenced by the number and type of home occupants. We cannot found the same microorganisms in a house with two persons than in other one with a family of seven. In addition, is has observed that not found the same microorganisms in homes where there is greater number of women that in which there is greater numer of males. Usually, mens released more microorganisms to environment.

Graphic of the influence of the genre of the occupants in the diversity of microorganisms in our home (Image: Albert barberán).

Another important factor that determines this geographical distribution and microbial diversity is the presence of pets. If in our homes we have animals like cats or dogs, we will found more varied microbial communities. In these case, these microorganisms are related to feces, skin and glans of these animals.

Differences in the abundance of certain bacterial species based on the presence or absence of pets (Image: Albert barberán).

Although the main source of emission are the occupants of these homes, microscopic comminities that colonise all corners are closely related to which we can found on the outside. In the case of fungi, this relationship is more narrow that in the case of bacteria. Even so, it has been observed that species are more varied in houses.

Comparison of the rich bacterial and fungal of our homes and the foreign. (Image: Albert barberán)

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How much reason have the phrase “as my home any place! Each home is indeed aunique and specific universe of microscopic communities. There aren’t two equal in the world!

REFERENCES

• Robert, D. Dunn. Home life: Factors Structuring the bacterial diversity found within and between homes.
• Albert Barberán. The ecology of microscopic life in household dust.
• Gilberto E. Flores. Microbial biogeography of public restroom surfaces.
• Cover Photo: Microbe.net

Parasites: signs on our way

The mysteries of human evolution, their development and their movementsthroughout history continue to create great interest and expectation. There are stillmany things to discover and understand about ancient societies, but thanks to thehelp of the science we are increasingly closer. Can parasites of the past shed light on those communities? We will discover it in thehands of the paleoparasitology.

WHAT IS PALEOPARASITOLOGY?

This is a branch of paleontology that study parasitological evidences in archaeological records, i.e.,studying parasites or remains of these found in ancient archaeological sites. The objective of these studies is to shed light on the origin and evolution of parasitic diseases that exist, as well as determine their phylogenetic relationships.  The study of ancient parasites allows us to know socio-cultural aspects of ancient societies as for example their diets, their level of hygiene, if human  were nomadic or sedentary, their migrations etc.

The materials studied by the paleoparasitology are generally fossilized tissueremains, mummies, fossils, coprolites (feces mummified) or sediments that have been able to be in contact with those who were the hosts of these parasites.

Mummified human coprolites. (Image: M. Beltrame)

Find remains of a parasite in some of the samples is difficult, since the passage oftime destroys all evidence. Even so, usually eggs or Oocyst parasites found (since theyare forms of resistance that have managed to stay over the millennia).

A egg of a louse (Pediculus humanus) found in a mummy of Brazil (12,000 years old). B. egg of Trichuris sp. found in Cape virgins, Argentina (6000 years old). (Image: Araujo).

In certain cases, manuscripts and drawings of ancient societies have providedinformation on the presence of certain parasites, such as for example ceramics thatwe observe below, where lesions that presents a person who suffers from cutaneous leishmaniasis is faithfully represented. In the next image we see a fossilized skull which presents very similar lesions.

A. Modified image of a ceramic moche representing (red circle) lesions caused by leishmaniasis. (Image: Oscar Anton, Pinterest) B. mummified skull that shows very similar injuries. (Image: Karl J. Reinhard).

THE ARRIVAL TO AMERICA: HUMAN MIGRATIONS AND PARASITES

About 150,000 years ago appeared a new species of hominid in Africa: Homo sapiens. It began to expand in several waves to the rest of the continent, Europe, and Asia,carrying with them some parasites that had inherited from his ancestors (known as heirloom parasites). At the same time, they were acquiring along their journey a range of parasites due to interactions with other humans and animals (souvenir parasites).

Following the archaeological remains and parasitological  clues what ancient humans have left during their migrations, is possible to determine the routes followed by them. One of these routes was the arrival in the new world (America). We have always believed that the first inhabitants of the Americas came across the Beringia Strait (which joined at some point by ice Siberia with Alaska) about 13,000 years ago.

Representation of the path followed by the first American settlers by the Beringia Strait Bridge. (Image: The siberian Times).

A few very interesting parasites that can be found in the American archaeological remains are Trichuris trichiura (nematode known as whipworm  and Ancylostoma duodenale (hookworm). These parasites need tropical or subtropical climatic conditions since the eggs are expelled with faeces and mature in the ground.

A. At the top adult A. duodenale (Christopher Noble). At bottom we can view an A.duodenale egg (Image: Universidad Antioquia) B. Adult Trichuris trichiura (Invertebrate zoology Virtual collection) and at bottom its egg. (Microbiolgia blogspot).

How do they then survived the cold conditions of the regions of Siberia and Alaska in the last ice age? They could not. These parasites would have not survived those harsh climatic conditions, since to their maturation and transformation infective they need warm and moist environments. In addition, signs of infections not found by these parasites in Arctic populations, such as the Inuit.

So, researchers believe that migration across the Bering Strait was not the only one. Paleoparasitologic experts  Adauto Aráujo and Karl J. Reinhard proposed that there were two alternative routes. On the one hand proposed a costal route (along the coast, route b in the image) and a trans-pacific route (crossing the Pacific Ocean, route c). By these routes parasites had been able to survive and continue infecting humans.

The arrival of man in America routes proposed by Aráujo and Reinhard based on paleoparasitologic remains. (Image: Aráujo, et al.)

Could they have been already there? This question has an easy answer. These intestinal parasites are specific from man, therefore, they need human hosts to complete their life cycles. If there were no humans in America, surely there would be this kind of parasites.

Another  parasitological fact that confirm this theory is the presence of Enterobius vermicularis, popularly known as pinworm. This parasite was linked for the first time to the ancestors of Homo sapiens and throughout history, has coevolved with them to give rise to several different subspecies. On the American continent have been found remains of two lineages of E.vermicularis, that could be because arrived hominids from different places with different parasites. In this case, the parasite if he could get through the Beringia Strait, since its life cycle does not depend so strongly on the environmental conditions.

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“Parasites suffer the same phenomena for evolution that humans and other organisms, as selection, extinction and colonization. For this reason, these specific parasites of man are excellent evidence that shed light on the movements of our ancestors”Adauto Aráujo, 2008.

REFERENCES

• A, Aráujo (2008). Parasites as Probes for Prehistoric Human Migrations?. Trends In Parasitology. Vol 24 (3). Pages: 112-115.
• Karl, J. Reinhard (2008). Archaeoparasitology. Encyclopedia of Archaeology, p. 494-501, ed. por Deborah M. Pearsall.
• CDC. Laboratory Identification of Parasitic Diseases of Public Health Concern. (En inglés).
• Cover photo: Chris Stringer, Natural History  Museum (Londres)

Bioluminescence: shining light

Some of the most commented images of landscapes are the known as “seas of stars” of Jervis Bay (Australia) or the caves of stars in New Zealand. Places that glow in the dark. Is it a photomontage? In fact, it is a natural process whereby organisms that have the ability to shine with their own light.

A fascinating sea of stars in Jervis Bay (image: maxres) B. Waitomo Glowworms cave in New Zealand (image: Forevergone).

WHAT IS BIOLUMINESCENCE?

Although it seems a magical landscape of a fairy tale, this is not a magical process. The bioluminescence is a type of chemiluminescence (chemical production process of light) by which living organisms are capable of producing light. It must not be confused with fluorescence. The latter is characterized by the reception of aphoton of the medium which then is sent, while the bioluminescence is the production of lightby the same body.

Species of all kingdoms have this capability: bacteria, fungi, fish, insects etc. It is estimatedthat 90% of the species that live in the deepest regions of the ocean are capable ofproducing light. Marc Arenas talks about these fascinating organisms in his two articles “Voyage to thebottom os the deep sea I and II“. At ground level this number drops, yet we all know thecase of fireflies (family Lampyridae) and bioluminescent fungi (genus Amarillia, Mycena…).

Firefly (Fam Lampyridae) and fungus Mycena chlorophos. (Image: National Geographic)

The bioluminescence reaction is an oxidation that produces no heat. The organisms present a protein known as Luciferine which by the action of an enzyme luciferase, it is oxidized. In the next image we see a simple representation of this reaction. The luciferase allows Luciferine protein join to the oxygen. The resulting energy of this oxidation is emitted as light. To carry out this process organisms have to spend energy, consuming ATP (energy molecule used for the functioning of the cells).

The bioluminescence scheme (Image: the HuffPostworks)

There are two different types of bioluminescence: intracellular (the chemical reaction occurs in specialized bodies) and extracellular (molecules are synthesized in the body and are then expelled to the outside where the reaction occurs). In the case of the intracellular, we can find those organisms that synthesize the necessary molecules or those that have a symbiotic relationship with luminescent bacteria.

BIOLUMINESCENCE FUNCTIONS

As we have said, the majority of organisms that have the ability to synthesize its own light live in dark places (caves, deep ocean…). These creatures have had to adapt to these harsh conditions. The bioluminescence is used for a wide variety of situations.

• Intraspecific communication. Used for communication between organisms of the same species, e.g. for mating. In the article “How do insects communicate?” Irene tells of the different methods used, including bioluminescence, used by the fireflies.

• Defense. There are certain living organisms that being disturbed or attacked produce light intracellularly or extracellularly to scare away the predator. A very interesting example is Vampire squid (Vampyrotethis infernalis) that spits out a bioluminescent mucus to fool predators.

• Attracting the prey. Certain organisms possess organs producing light that attract their prey. As for example the belonging to the genus Lophiiformes.

• Camouflage. In certain cases the bioluminescence is used for camouflage in the shadows of the ocean, it would be the case of lantershark.

BIOLUMINESCENCE IN MICROORGANISMS

Many microorganisms have the ability to produce their own light, and their intentions are not very different from the of higher organisms. In certain cases, the bioluminescence is used as a method of detoxification of the oxygen, i.e., a simple way to remove the excess oxygen. In others, used as a method of communication.

Some dinoflagellates, such as  Pyrodinium bahamense, have the ability to produce light when environmental conditions have been very favourable and its population has undergone exponential growth. At that time, when the water is moved the light reaction occurs as it would be the case of the famous beaches of stars.

Overgrowth of dinoflagellates which produce bioluminescence in the sea. (Image: Ies Rey Pelayo)

In the specialized organs of certain animals are strains of bacteria such as Vibrio fischeri or Photobacterium. These microorganisms receive nutrients from the animals and as a result of their metabolic activity,  produce light.

Image of the Hawaiian squid (Euprymna scolopes) and magnification of its light organ. Inside it, we can see bioluminescent bacteria Vibrio fischeri. (Image: Eric Stabb)

In many cases, the production of bacterial light is conditioned with population density, i.e. only produces light when there are many bacteria. This system of regulation is called quorum sensing.  But, what is it?

 QUORUM SENSING

Microorganisms release inducing substances (favor a process) to the environment. When the concentration of these substances is very large due to a high population density, activate certain processes regulated genetically, as it would be the case of the bioluminescence.

This is a form of communication among microorganisms, since many processes depend on population density. In the case of Vibrio Fischeri, this only produces light when the population density has reached a certain size. When inducing molecules come in contact with bacteria, begins a genetic process that regulates the production of the enzyme luciferase and, therefore, the bioluminescence.

Image of the bioluminescence simplified genetic process regulated by quorum sensing. (Image: Cornell Institute for Biology teachers).

BIOTECHNOLOGY AND BIOLUMINESCENCE

Biomimicry, science uses nature as a source of inspiration to create technologies that solve human problems, it has the adaptation of these mechanisms of lighting as next frontier. Do you imagine to replace the streetlights by bioluminescent trees?

Currently it is not possible yet, but there are large companies that focus their efforts on changing cities electricity by cheaper and renewable energy. Through the genetic modification of plants, it would introduce the gene responsible for the bioluminescence and these plants would be capable of producing light.

Recreation of the lighting of the future with bioluminescent plants. (Image: iluminet)

This form of energy, apart from reducing energy costs and pollution, is quick and simple to maintain. Only through a nutrient-rich gel and a colony of Vibrio fischeri could have a brilliant and continuous lighting. Is this the new way of lighting in our cities?

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Nature is majestic and continues to give us lessons, you just have to learn to observe.

REFERENCES

• Brock, biología de los microorganismos. Michael T, Madigan. Ed. Pearson. (Spanish)
• Ocean Today. NOAA.
• The bioluminescence Web Page.
• Cover Photo: Andy Hutchinson

Basic Microbiology (I): invisible world

The 7 September 1674 Anton van Leeuwenhoek said having watched a few tiny animals in a drop of water. What you referred to the concept of tiny animals? In many of our articles we refer to these organisms. Read on to start your journey into the fascinating world of the invisible. 

A MICROSCOPIC WORLD

“They are imperceptible to the naked eye and abounded in such a way that the water seemed to be alive.” From a simple sample of water, Anton Leeuwenhoek concluded that there were tiny living organisms that were impossible to observe with the naked eye. With the help of a rudimentary microscope, he described the first microorganisms.

A world microscopic drawings of Leeuwenhoek over what he described as tiny animals. (Photo: Miguel Vicente, Madrimasd).

The concept of microorganism refers to a heterogeneous group of organisms that can only be displayed with the help of microscopes, since they have sizes lower than the limits of vision of humans (approximately 0.1 mm). They may be prokaryotic (bacteria), eukaryotic (Protozoa, algae, fungi…) and even entities acellular, as it would be the case of the virus. These organisms are measured by submultiples of the metro, more specifically in micrometers (μm, thousandth of a millimeter) and nanometers (nm, millionth of a millimeter).

The submultiples of the metro table (photo: Science Park).

This small size has its advantages: a high surface to volume ratio. This factor has an important biological effect. For example, the smaller cells tend to grow and multiply more quickly due to a rapid exchange of nutrients. Be reduced in size on the other hand, favors a more rapid evolution already that to multiply more quickly significantly increases the frequency of mutations (remember that mutations are the raw material of evolution). In addition, microorganisms more quickly adapt to the environment.

Let’s look at the different sizes that can be found in this large group of microorganisms. In the image below we can see a simple comparison between the various organisms and cells.

Different microorganisms and cells size scale. (Photo: Isabel Etayo).

BACTERIA

This group of prokaryotes is characterized by a size that includes more than 700 μm and 0.2 μm. It should be noted that this group presents varied morphologies and therefore some are measured by diameter (spherical bacteria or coconuts) or by thickness and height (elongated bacteria or bacilli). A prokaryote’s average size is between 0.5 μm and 4 μm. The bacterium Escherichia coli is usually of approximately of 2 μm x 1 μm. In a small space, as the diameter of the point that there is at the end of this sentence would fit some 500 E. coli.

Size comparative diagram of different bacteria. (Photo: University of Granada).

The largest known bacterium is Thiomargarita namibiensis. This prokaryote was found in Namibia in 1999. Its size is 750 μm in diameter (0.75 mm), so they are almost visible to the naked eye. These microorganisms usually present as large as some nutrient storage mechanism, in this case sulfur. Another great example is that of Epulopiscium fishelsoni with a size of 600 μm. On the right side of the picture below we can see the comparison of the latter with  E. coli.

A. Picture of Thiomargarita namibiensis, of about 750 micrometers. B. comparison between Epulopiscium fishelsoni and E. coli. (Photos: Science Policy)

Having a microscopic size isn’t all advantages, it is obvious that there should be a lower limit. Sizes less than 0.15 μm in a bacterium would be almost impossible. Mycoplasma pneumoniae is the smallest bacterium, with a diameter of 0.2 μm. This is a bacterium without a cell wall which can be purchased in many different ways. Following the example of the final point, at 1 mm diameter would fit 5000 bacteria size of Mycoplasma pneumoniae.

VIRUSES

In general, viruses have sizes much smaller than bacteria. They usually have sizes ranging from 20 to 300 nm. So the virus can be up to one hundred times smaller than a bacterium like E. coli. 

Comparison of sizes of different virus and E. coli. (Photo: diversidad microbiana)

The largest known virus is the Mimivirus. This presents 600 nm in diameter (larger than Mycoplasma pneumoniae). In the image below, you can see the comparison between the size of these giant virus and Rickettsia conorii (bacteria that causes human Boutonneuse Fever).

Comparison between Mimivirus and Rickettsia conorii. (Photo: byte Size Biology)

The Polio virus is one of the smallest viruses that are known, with a size of 20 nm (0.02 μm). If we could observe how many polio virus would fit on the point of the end of the sentence, would find some 50000 polio viral particles.

MICROSCOPIC EUKARYOTES

In Protozoa, the size remains varied. The average size is usually 250 μm in length. Even so, small protozoa as bacteria can be found (between 2 and 3 μm, like for example the Leishmania or Babesia) or large protozoa visible to the naked eye (from 16 mm in the case of Porospora gigantea). In the case of Leishmania can be seen as almost a hundred of bodies (thin arrow) can live inside a macrophage of a 30 μm (coarse black arrow).

Leishmania inside a macrophage (black arrow). The bar represents about 20 micrometers. (Photo: Thatawan Pothirat).

Microscopic fungi, such as yeasts, include sizes 6-20 μm. The best-known yeast is Saccharomyces cerevisiae with a size of oscillates between the 6 and 12 μm depending on its stage of ripeness. In the image below we can see an example very clear.

Size of the cells of Saccharomyces cerevisiae. (Photo: Easy notes).

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“No view has reached my eye more pleasurable than this of so many living creatures within a small drop of water”. Anton Leeuwenhoek, in 1974, discovered an incredible invisible world.

REFERENCES

• Brock, Biología de los microorganismos. Editorial Pearson.
• Ignacio López-Goñi. Virus y Pandemias. Editorial Naukas.
• Cover Photo: Escuela y Ciencia.

The killer fungus: the nightmare of the amphibians

In recent years, the populations of amphibians around the world have suffered a major decline, to the point that many of them disappear completely. Many researchers are running that the loss of these populations is due to several factors: climate change, habitat loss and the presence of a parasitic fungus. In this article will announce the parasite known as killer fungus.

BATRACHOCYTRIUM DENDROBATIDIS 

This is the scientific name given to this fungus. It belongs to the class Chytridiomycetes, which gathers fungus parasites of plants and invertebrates. However, this is the only one of this kind affecting vertebrate organisms. It is related to the disappearance of more than 200 species of amphibians, including the golden toad of Costa Rica.

One of the latest images that we have of the golden toad (Almirante periglenes). (Photo: Richard K.)

It has a life cycle that consists of two phases: a stationary (sporangium) and one mobile (via zoospores). In the image below we can see an outline of the structure of this type of fungi. The sporangium has some fine extensions known as rhizoids or mycelium rizoidal that allows to anchor itself in the inner skin layer. The zoospore emerges from the sporangium when it matures and presents a single apical flagellum.

Diagram of the structure of the fungus Bd. (photo: trilobite glassworks)

Batrachocytrium dedrobatidis is a parasite and need a host that provide nutrients. In this case, the fungus feeds on keratin of skin of amphibians. Zoospores arrives to the skin of the host by water and encyst in the areas with greatest amount of keratin. They lose the flagel and become a sporangium. They develop the mycelium and again produce zoospores that emerge into the water. In the event that there are no hosts around, the parasite becomes a saprophyte (feeds on organic matter in decomposition) waiting for the arrival of new amphibians.

Life cycle of B. dendrobatidis. (Photo: Roseblum)

Why this process results in a disease for amphibians?

CHYTRIDIOMYCOSIS

In amphibians, the skin is one of the most important organs. It develops functions such as hydration, osmoregulation, the thermoregulation and breathing (for example, the lissamphibians breathe only through the skin. Discover them in this article). Fungus feeds on keratin of skin, destroys the upper layers and spread over all body surface, preventing this organ to perform ion exchange. Individuals die from cardiac arrest.

Image of microscopy of skin of an amphibian stricken with chytridiomycosis. The arrows indicate the sporangia. (Photo: Che Weldon)

The sporangia are attached to keratinized skin areas, which get their nutrients. Approximately between 4 and 6 days after infection, they begin to develop the zoospores (black areas in the interior of the sporangia of the image above).When these spores have matured, are released through a spout that is initially closed. Stopper (bottom image) dissolves shortly before the release of zoospores.

Image of the surface of the skin of a frog by electronic scanner. The papillae of the sporangium are identified with a triangle. The black arrow indicates a sporangium with the plug dissolved. (Photo: Berger).

This disease affects only adult specimens. Even so, tadpoles are reservoirs of the disease, so they can become infected but do not develop symptoms. The fungus infects the tadpole keratinized areas (normally the areas of the mouth) and when the metamorphosis takes place, the fungus expands to other areas.

GEOGRAPHIC EXPANSION: ARRIVAL TO SPAIN

The fungus is characteristic of South African populations of Xenopus laevis (African Toad of nails, used in research), but spread all over the world through the traffic from infected individuals. The situation is so serious and the world Organization for Animal Health (OiE) has classified chytridiomycosis as a notifiable disease. In addition B. dendrobatidis is included in the list of 100 most invasive exotic species by the IUCN (if you want to know that they are invasive species, please read the following article).

World regions which have been confirmed positive cases of chytridiomycosis. (Photo: Bd-maps).

Spain was the first European country to suffer an outbreak of chytridiomycosis, particularly in the Parque Natural de Peñalara in Madrid. The common midwife toad (Alytes obstetricans) was the most affected. Positive cases in other Spanish regions, as for example in the Balearic Islands have also been found. There are many investigations underway to solve this problem, like for example of Project Zero of the CSIC General Foundation.

Positive amphibians to chytridiomycosis in Spain (photo: Bd-maps)

THE CASE OF THE BALEARIC MIDWIFE TOAD

The Balearic midwife Toad  (Alytes muletensis) is endemic to the Balearic Islands. It is classified as a vulnerable species by the IUCN (in this article we talk about this organization and its red list of species). It lives in ponds and ravines of difficult access in the Serra de Tramuntana (Mallorca). Specimens can reach around 4 cm and are nocturnal. Generally, this species was threatened by the destruction of their habitat or predation, but the latest threat facing it is chytridiomycosis.

Balearic midwife Toad or ferreret (photo: Guillem Gutiérrez).

Researchers found that certain populations experienced a significant decrease in the number of specimens, and they appeared dead without apparent reason. Studies revealed that these deaths were due to the presence of the parasitic fungus B.dendrobatidis. The population that presented more problems was the belonging to the area known as Torrent dels Ferrets (in 2004 it was confirmed the first case of chytridiomycosis).

Evolution of the population of Alytes muletensis in the Torrent dels Ferrerets. There have been deaths by Bd since 2004 (photo: Joan Mayol)

Research to ending this fungus has been a success. At the end of 2015, researchers from the Balearic Islands confirmed the first successful treatment against chytridiomycosis. They carried out disinfection in the natural environment (to eliminate any presence of zoospore) and combined it with an anti-fungal treatment to tadpoles. They managed to completely eliminate the presence of the parasite, and thus save the population. Even so, efforts to put an end to this fungus should not cease.

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Chytridiomycosis is still a serious problem for global amphibian populations, but there is still hope. 

REFERENCES

• World organisation for animal health (OiE)
• CSIC General Foundation: Lucha sin cuartel contra la quitridiomicosis (spanish), by Jaume Bosch.
• 100 of the most invasive alien species in the world, ISSG. PDF
• The Mallorcan midwife Toad, from discovery to conservation, Joan Mayol and Joan Oliver. (Spanish)
• Cover Photo: Vance Vredenburg.