Arxiu d'etiquetes: yeast

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. 


“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).


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.


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.


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).


“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.


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


Alcoholic fermentation of plants through cultures

All cultures around the world have based their diet and culture in plants of their environment. So, each people way of cooking, dressing, building our house, healing or making instruments to create music is related to raw materials available: the plants of our landscape.

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Ethnobotany is the science that studies the cultural uses of vegetation over time and in this post I want to talk about a cultural use of plants spread around the cultures of the world: the production of alcoholic beverages through the process of fermentation and/or distillation of plants sweet juice.


The fermentation process is done by the yeast metabolism that produces energy from sugars. This is the way how these living beings produce their own energy in an anoxygenic environment; for this is called anaerobic metabolism. Other waste products of fermentation are carbon dioxide (CO2); that’s why we found gas in beers, for example, and of course, alcohol.

Culture plate with yeast Saccharomyces cerevisae (Foto: Wikimedia Comons)
Culture plate with yeast Saccharomyces cerevisae (Foto: Wikimedia Comons)

The fermentation has been used to preserve and enhance the flavors of a variety of foods throughout history, such as bread, yogurt, tofu, soy sauce or cheese (which have lost their alcohol).

The main responsible of this type of fermentation in the food industry is Saccharomyces cerevisae, although there are other yeast species and genera able to perform the alcoholic fermentation giving foods its distinctive taste.

The alcoholic distillation process is really distinct from fermentation. Distillation is a chemical process that separates the components of a liquid mixture by a heat source. The different components of a solution are separated in an alembic through evaporation and condensation according to their volatility. In the case of alcoholic beverages, distilled spirits are produced to obtain drinks with more alcohol, from juice of the fermented grain or fruit. For example, the brandy is distilled wine.

Alembic used to ditillate fluids (Foto: barresfotonatura)

So I invite you to take a journey through the world of spirits under this classification… All the continents have come to produce alcohol by this process? What do you think?


Among the beverages produced by alcohcolic fermentation in the Mediterranean, the wine is the most famous. Wine is a product of the fermentation of grape juice. The grapes come from vine (Vitis vinifera); a shrub native to the Caucasus and the Middle East that has also been used as a shade plant because it is a plant that climbs easily. There are over 10,000 varieties of grapes used to produce a wide range of wines. The wine art has been exported to other countries around the world with a Mediterranean climate, and therefore which can easily grow grapes, such as California, Chile, South Africa and Australia. The alcohol content of wine ranges from 10º to 14º.

To produce cava or champagne the sugars left in the wine bottle undergo a second fermentation (brut nature champagne). If sugars not coming from grapes are added to trigger this process then we are talking about brut or extra brut champagne. Then, yeast will begin the alcoholic fermentation again, producing dioxide carbonide and thus generating this drink typical bubbles.

Grape from Macabeu variety (Foto: barresfotonatura)

Another highly consumed beverage worldwide resulting from the metabolism of the yeast is beer, which is produced from the fermentation of barley (Hordeum vulgare) and finally adding hops (Humulus lupulus), which provides bitterness. The beer can be drunk hot or cold and its alcohol content varies from 2.5º to 11º. Currently, many different brands of beer mix different cereals in their fabrication (such as maize and rice) but do not be deceived, the original is made just with barley!

Female cones from hop plant (Cannabaceae) used to bitter beer and also to facilitate its conservation (Foto: Wikimedia Comons)

If we travel a little more further, exotic flavors of the east can also get drunk. Japan came to produce alcohol from rice (Oryza sativa), the most consumed cereal in Asia. It’s sake, an alcoholic beverage from 14º to 20º degrees that you can also drink hot or cold.

Rice crop field (Foto: barresfotonatura)

In Mexico we can also found a fermented drink that comes from a native plant. It is the mescal, obtained from Agave tequilana a native agave in Mexico. In this case the juice that originates the drink doesn’t come from the fruit, but from the base of its succulent leaves (called piña) containing a high concentration of sugars. The mescal is one of the alcoholic beverages with more alcohol (55º). The process of distillation of the mescal produces the popular tequila, which has an alcohol content of 37º to 45º. The fermentation of the agave to make pulque or mescal was already known by the Mexica but the distillation process did not occur until the arrival of the Spanish colonizers and its alembics in the S. XVI.

Agave tequilana crop field and “piñas” from where sweet juice is extracted to make the fermantated beverage (Foto: barresfotonatura)


Going back to the Old World, in the cold and continental lands of Europe, people have also arrived to ​​distillate the fermented juice of some plant found in the environment to produce an alcoholic beverage. In this case, I’m talking about vodka, a distillate of wheat (Tricticum sativum) or rye (Secale cereale) that can also be made from potato (Solanum tuberosum), one of the easiest and cheapest crop in cold. The graduation is quite high, up to 45 degrees.

Moreover the islands of Ireland and Scotland, came to distill the juice of barley (Hordeum vulgare), to produce whiskey; with more than 40º.

Barley (Hordeum vulgare) crop field (Foto: barresfotonatura)

In the Caribbean and especially Cuba, there is a distillate with a completely different origin, rum, obtained from sugar cane (Saccharum officinarum). The history of this drink involves invasions, slavery and has no relationship with native plants, but rather with colonial history. Sugar cane is a plant of the family Poaceae (grasses) native to New Guinea and India. It was exported to the Caribbean islands by Spanish colonists in the sixteenth century because its cultivation in tropical climates allowed high performance. Its production was only supported by the exploitation of Africans slaves. The rum has37º to 43º alcohol degrees. The Brazilian version of the rum is cachaça, obtained from the same process as rum.

Sugar cane (Saccharum officinarum) crop field (Foto: barresfotonatura)
Sugar cane (Saccharum officinarum) crop field (Foto: barresfotonatura)

We have travelled to America, Europe and Asia through its fermented alcoholic culture…Somebody knows the same culture in Africa or Oceania?


  • Herbert Howell C & Raven PH (2009). Flora mirabilis. How have shaped world knowledge, health, welth and beauty. National Geographic and Missouri Botanical Garden.
  • Hough SJ (2001). Biotecnología de la cerveza y de la malta. Acribia, Zaragoza.
  • Parthasarathy N (1948). Origin of Noble Sugar-Canes (Saccharum officinarum). Nature 161: 608-608.
  • Robinson J, Harding J, Vouillamoz J (2012). Wine Grapes – A complete guide to 1,368 vine varieties, including their origins and flavours. Allen Lane, UK.


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