Microbiology

A cultivation of microorganisms in agar.

Microbiology is the science in charge of the study and analysis of microorganisms, tiny living beings invisible to the human eye (from the Greek «μικρος» mikros &# 34;small", «βιος» bios, "life" and «-λογία» -logy, treatise, study, science), also known as microbes. It is dedicated to studying organisms that are only visible through a microscope: prokaryotic organisms and simple eukaryotes. Microbes are considered all those microscopic living beings, these can be made up of a single cell (unicellular), as well as small cellular aggregates made up of equivalent cells (without cell differentiation); these can be eukaryotes (cells that have a nuclear envelope) such as fungi and protists; and prokaryotes (cells without a nuclear envelope) such as bacteria. However, traditional microbiology has dealt especially with pathogenic microorganisms among bacteria, viruses and fungi, leaving other microorganisms in the hands of parasitology and other categories of biology.

Blood grab, cultivation Staphylococcus aureus.

Although the current knowledge of microbiology is extensive, much remains to be learned and new discoveries are constantly being made in this field. So much so that, according to the most common estimates, only 1% of the microbes existing in the biosphere have been studied so far. Therefore, despite the fact that more than 300 years have passed since the discovery of microorganisms, the science of microbiology is still in its infancy compared to other biological disciplines such as zoology, botany or even entomology.

By dealing with microbiology, especially pathogenic microorganisms for humans, it is related to medical categories such as pathology, immunology, and epidemiology.

History

Buffon microscope in Paris

Microbiology, as a science, has existed since roughly the second half of the 19th century. In the III century BC, Theophrastus, Aristotle's successor at the Lyceum, wrote thick volumes on the healing properties of the plants. Although the term bacteria, derived from the Greek βακτηριον ("rod"), was not introduced until 1828 by Christian Gottfried Ehrenberg, already in 1676 Anton van Leeuwenhoek, using a single-lens microscope that he himself had built based on the model created by scholar Robert Hooke in his book Micrographia, it made the first recorded microbiological observation of "animacules," as van Leeuwenhoek then called and drew them.

Eugenio Espejo (1747-1795) published important medical works, such as Reflections on smallpox (1785), which would become the first scientific text referring to the existence of microorganisms (even before Louis Pasteur) and who would define current basic concepts such as asepsis and antisepsis of places and people as health policy.

Bacteriology (later a subdiscipline of microbiology) is considered to be founded by the botanist Ferdinand Cohn (1828-1898). Cohn was also the first to formulate a scheme for the taxonomic classification of bacteria.

Louis Pasteur (1822-1895), considered the father of Medical Microbiology, and Robert Koch (1843-1910) were contemporaries of Cohn. Perhaps Pasteur's greatest triumph was his refutation by careful experiments of the then highly respected theory of spontaneous generation, establishing microbiology firmly within the biological sciences. Pasteur also designed methods for food preservation (pasteurization) and vaccines against various diseases such as anthrax, avian cholera, and rabies. Robert Koch is especially known for his contribution to the germ theory of disease, where, by applying the so-called Koch postulates, he succeeded in demonstrating that specific diseases are caused by specific pathogenic microorganisms. Koch was one of the first scientists to focus on obtaining pure cultures of bacteria, which enabled him to isolate and describe several new species of bacteria, including Mycobacterium tuberculosis,Pasteurization the causative agent of tuberculosis.

While Louis Pasteur and Robert Koch are often considered the founders of microbiology, their work did not accurately reflect the true diversity of the microbial world, given their exclusive focus on microorganisms of medical relevance. Such diversity was not revealed until later, with the work of Martinus Beijerinck (1851-1931) and Sergei Winogradsky (1856-1953). Martinus Beijerinck made two great contributions to microbiology: the discovery of viruses and the development of microbiological culture techniques. While his work with tobacco mosaic virus established the basic principles of virology, it was his development of new cultivation methods that had the greatest immediate impact, allowing the cultivation of a wide variety of microbes that had hitherto not been available. could be isolated. Sergei Winogradsky was the first to develop the concept of chemolithotrophy and thereby reveal the essential role that microorganisms play in geochemical processes. He was responsible for the isolation and description for the first time of both nitrifying and nitrogen-fixing bacteria.

The English surgeon Joseph Lister (1827-1912) provided indirect evidence that microorganisms were agents of human disease through his studies on the prevention of wound infections. Lister, impressed by Pasteur's research on the participation of microorganisms in fermentation and putrefaction, developed a method of antiseptic surgery, in order to prevent microorganisms from penetrating wounds. Instruments were heat sterilized and surgical dressings were treated with phenol, which was occasionally used to spray the surgical field. This method had very satisfactory results and transformed surgery after Lister published his results in 1867. At the same time, it provided indirect evidence on the role of microorganisms in diseases, since phenol, which destroyed bacteria, prevented infections in the wounds.

Empiricism and speculation

Human knowledge about the effects produced by microorganisms has been present even before being aware of their existence; Due to fermentation processes caused by yeast, bread, alcoholic beverages and milk products can be made. In ancient times the cause of diseases was attributed to divine punishment, supernatural forces or physical factors (The word malaria means "bad air", it was believed that it was the stale air of the swamps that caused this disease). During this period before the discovery of microorganisms, naturalists could only speculate about the origin of diseases.

Types of microbiology

The field of microbiology can be divided into several sub-disciplines:

• Microbial physiology: study (at the biochemical level) of the functioning of microbial cells. It includes the study of growth, metabolism and regulation of this. Closely related to microbial genetics.
• Microbial genetics: study of the organization and regulation of microbial genes and how these regulate the functioning of cells. It's very related to molecular biology.
• Medical microbiology: study of microorganisms that cause diseases in the human being, their transmission, pathogenesis and their treatment. Very related to medicine, epidemiology, pharmacology and public health.
• Veterinary microbiology: study of microorganisms that cause diseases in animals, mainly in domestic and economic interests (reses, poultry, pigs, sheep, goats, etc.).
• Environmental microbiology: study of the function and diversity of microbes in their natural environments. It includes microbial ecology, geomicrobiology, microbial diversity and bioremediation.
• Evolutionary microbiology: study of the evolution of microbes. It includes systematic and bacterial taxonomy.
• Industrial microbiology: studies the exploitation of microorganisms for use in industrial processes. Examples are industrial fermentation (obtaining alcoholic beverages), wastewater treatment, the production of biological (vacunas, antidotes) and the production of foods such as yogurt, cheese, etc. Very close to the biotechnology industry, since genetic engineering techniques overestimate the production of certain microbial metabolites of economic interest (amino acids, antibiotics, organic acids, vitamins, etc.).
• Pharmaceutical microbiology:studies microorganisms associated with the manufacture of pharmaceutical products.
• Food Microbiology: Microbiological food analysis is an effective tool in accepting a process. The interpretation of the results obtained in the laboratory is the most complex of the evaluation process.
• Health microbiology: study of the microorganisms that contaminate the food and that spoil them or through which they can transmit diseases to those who consume them.
• Agricultural microbiology: study of microorganisms (especially fungi and bacteria) found in soils for the cultivation of plants of economic interest and how they interact together in a beneficial way.
• Fitopathology: study of diseases that certain species of microorganisms (virus, bacteria, fungi, protists and nematodes) cause in plants, mainly in those of economic interest.
• Microbial ecology: studies the behavior of populations of microorganisms when they interact in the same environment, establishing biological relations between themselves.

Subdisciplines and other related disciplines

• Bacteriology: Study of proximates (bacteria, archaees). It also covers the study of mycobacteria (micobacteriology).
• Virology: Study of viruses.
• Micology: Study of mushrooms.
• Protozoology: Protozoan study.
• Micropaleontology: Study of microfossils.
• Palinology: Study of pollen and spores.
• Physics: Also called Algology, is the study of algae and microalgae.

Benefits of microbiology

Fermenter tanks with yeast being used to prepare beer.

Historically, microorganisms have been viewed negatively because of their association with many human and animal diseases. However, pathological microorganisms are a very minor percentage within the total number of microorganisms, most of which play absolutely essential roles and which, if they did not exist, would make life on Earth unfeasible. Some examples are bacteria that fix atmospheric nitrogen (enabling the life of plant organisms), carbon cycle bacteria (essential for reincorporating organic matter into the soil) or the multitude of microorganisms that live symbiotically in our digestive tract, without which digestion would not be viable. Thus, the "higher organisms" (animals, plants, etc.) we could not live if it were not for the functions carried out by these microscopic beings. In addition, they have wide applications in the industrial field, such as fermentation (for example, for the production of alcoholic beverages or dairy products), the production of antibiotics or other products of pharmaceutical or biotechnological interest (hormones, enzymes, etc.). Finally, it is also worth noting the essential role that microorganisms play in biological research laboratories around the world as tools for gene cloning and protein production.

Refutation of the theory of spontaneous generation

Autoclave: equipment used to sterilize crop materials and mediums.

In the 19th century there was a great controversy about the theory of spontaneous generation. The basic idea of spontaneous generation can be easily understood. The food rots if it remains for a certain time outdoors. When this putrid material is examined under a microscope, it is found to be teeming with bacteria. Where do these bacteria that you don't see in fresh food come from? Some thought that they came from seeds or germs that reached the food through the air, while others thought that they originated spontaneously from inert material.

The most ardent opponent of spontaneous generation was the French chemist Louis Pasteur, whose work on this problem was the most rigorous and convincing. First, Pasteur showed that there were structures in the air that closely resembled the microorganisms found in putrefied material. He discovered that normal air continually contains a diversity of microbial cells that are indistinguishable from those found in much greater numbers in putrefying materials. Therefore, he concluded that the organisms found on such materials originated from microorganisms present in the air. He further postulated that these suspended cells are constantly deposited on all objects. Pasteur thought that if his conclusions were correct, then a treated food should not spoil, in such a way that all organisms that contaminate it were destroyed.

Pasteur used heat to remove contaminants, as it was already known that heat effectively destroys living organisms. In fact, other researchers had already shown that if a nutrient solution was placed in a glass flask, sealed, and then heated to a boil, it never decomposed. Advocates of spontaneous generation criticized such experiments arguing that fresh air was needed for spontaneous generation and that the air inside the closed flask was changed by heating so that it was not capable of spontaneous generation. Pasteur overcame this objection simply and brilliantly by constructing a swan-necked flask, now designated a Pasteur flask. In such vessels, nutrient solutions could be heated to a boil; then, when the flask cooled, air could enter again, but the curvature of the neck of the flask prevented particulate matter, bacteria, and other microorganisms from reaching the interior of the flask. The sterilized material in such a container did not decompose and microorganisms did not appear as long as the neck of the flask did not come into contact with the sterile liquid. However, it was enough for the neck of the flask to tilt enough to allow the sterile liquid to contact the neck, for putrefaction to occur and the liquid to fill with microorganisms. This simple experiment was enough to definitively clear up the controversy over spontaneous generation.

Removing all bacteria or microorganisms from an object is a process we now call sterilization. The procedures used by Pasteur, Cohn, and other investigators were eventually improved upon and applied to microbiological research. The end of the theory of spontaneous generation therefore led to the development of effective sterilization procedures, without which microbiology could not have developed as a science.

Microbiology today

Currently, microbiological knowledge has become so specialized that we find it divided: medical microbiology studies pathogenic microorganisms and the possible cure for the diseases they cause, immunology finds out the causes of the appearance of diseases from an immunological perspective, ecological microbiology studies the niche that corresponds to microorganisms in the environment, agricultural microbiology the relationships between plants and microorganisms, and biotechnology the possible benefits that the exploitation of microbes can bring to man.

Importance

Microbiologists have made contributions to biology and medicine, especially in the fields of biochemistry, genetics, and cell biology. Microorganisms have many characteristics that make them "model organisms" ideals:

• They are small, so they do not consume many resources.
• Some have very short generation times: the time needed for a bacterial cell to be divided into two in optimal conditions is approximately 20 minutes for E. coli in a rich medium and 37 °C. However, there are bacteria with longer generation times, like Mycobacterium tuberculosisIt's 12 to 24 hours.
• Cells can easily survive separated from other cells.
• Unicellular eukaryants are reproduced by mitotic division and procariot by binary fission. This allows the spread of genetically equal conical populations.
• They can be stored by freezing for large periods of time. Alicuots are usually prepared containing millions of micro-organisms per milliliter, so even if 90% of the cells die in the freezing process, viable cells could still be obtained.

The importance of microbiology is based on its repercussions in various aspects of daily life, which are not exclusively limited to health sciences. On the contrary, the knowledge of microscopic life forms generates an impact in areas such as industry, energy resources and public administration. Although the existence of microorganisms has been postulated since ancient times, it was undoubtedly Luis Pasteur who was in charge of systematizing the current concepts of microbiology, destroying the ideas of spontaneous generation and highlighting the real importance of this science. Currently, the growth of microbiology as a branch has been such that many specialists have chosen to divide it and, thus, consider clinical microbiology, general microbiology, microparasitology and mycology, among others, as independent disciplines.

Complementary bibliography

• Kreft, J.-U.; Plugge, C. M.; Grimm, V.; Prats, C.; Leveau, J. H. J. «Mighty small: Observing and modeling individual microbes becomes big science»Proceedings of the National Academy of Sciences, 110, 45, 05-11-2013, pàg. 18027–18028. DOI: 10.1073/pnas.1317472110. ISSN: 0027-8424. PMC: PMC3831448. PMID: 24194530.
• Madigan M.T., Martinko J.M., Dunlap P-V., Clark D.P. 2009. Brock. Biology of microorganisms. Pearson Education, Madrid, pp. 1296