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the science that deals with living things. It is broadly divided into zoology, the study of animal life, and botany, the study of plant life. Subdivisions of each of these sciences include cytology (the study of cells), histology (the study of tissues), anatomy or
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The multidisciplinary science of microorganisms. The prefix micro generally refers to an object sufficiently small that a microscope is required for visualization. In the seventeenth century, Anton van Leeuwenhoek first documented observations of bacteria by using finely ground lenses. Bacteriology, as a precursor science to microbiology, was based on Louis Pasteur's pioneering studies in the nineteenth century, when it was demonstrated that microbes as minute simple living organisms were an integral part of the biosphere involved in fermentation and disease. Microbiology matured into a scientific discipline when students of Pasteur, Robert Koch, and others sustained microbes on various organic substrates and determined that microbes caused chemical changes in the basal nutrients to derive energy for growth. Modern microbiology continued to evolve from bacteriology by encompassing the identification, classification, and study of the structure and function of a wide range of microorganisms including protozoa, algae, fungi, viruses, rickettsia, and parasites as well as bacteria. The comprehensive range of organisms is reflected in the major subdivisions of microbiology, which include medical, industrial, agricultural, food, and dairy. See Algae, Bacteriology, Biotechnology, Fungi, Immunology, Industrial microbiology, Medical bacteriology, Medical mycology, Medical parasitology, Protozoa, Rickettsioses, Virus
the science of microorganisms—bacteria, mycoplasms, actinomycetes, yeasts, microscopic fungi, and algae—that is, their taxonomy, morphology, physiology, biochemistry, genetics and variability, distribution and role in the natural cycle of matter, and practical significance.
Origin and development. For thousands of years before microbiology emerged, man, although unaware of the existence of microorganisms as such, used microbes widely to prepare koumiss and other fermented-milk products, to produce wine, beer, and vinegar, to ensile fodders, and to ret flax. Bacteria and yeast cells were observed for the first time by A. van Leeuwenhoek, who examined dental plaque, plant infusions, and beer with the aid of microscopes he had developed.
The creator of microbiology was L. Pasteur, who elucidated the role of microorganisms in fermentation (viniculture, brewing) and in the origin of animal and human diseases.
Pasteur’s method of preventive vaccination—injecting the subject with attenuated cultures of pathogenic microorganisms—was of exceptional importance in controlling infectious diseases. Long before the discovery of viruses, Pasteur proposed vaccination against what was in fact a viral disease: rabies. It was he also who proved that the spontaneous generation of life is impossible on earth today. Pasteur’s works served as the scientific basis for the sterilization of surgical instruments and dressings, for canned goods manufacture, and for the pasteurization of food products.
Pasteur’s ideas of the role of microorganisms in the natural cycle of matter were developed further by the founder of general microbiology in Russia, S. N. Vinogradskii, who discovered chemoautotrophic microorganisms (which metabolize atmospheric carbon dioxide, using the oxidation energy of inorganic matter), nitrogen-fixing microorganisms, and aerobic cellulose-decomposing bacteria. His pupil V. L. Omelianskii discovered anaerobic cellulose-fermenting bacteria (anaerobic decomposition) and methane-forming bacteria.
A substantial contribution to the development of microbiology was made by the Dutch school of microbiologists, who studied the ecology, physiology, and biochemistry of various groups of microorganisms (M. Beyerinck, A. Kluyver, C. van Kiel). An important role in the development of medical microbiology was played by R. Koch, who proposed solid nutrient media for culturing microorganisms and discovered the causative agents of tuberculosis and cholera. The development of medical microbiology and immunology was promoted by E. Behring in Germany, E. Roux in France, S. Kitasato in Japan, and E. Metchnikoff, L. A. Tarasevich, D. K. Zabolotnyi, and N. F. Gamaleia in Russia and the USSR.
The development of microbiology itself, like the development of practical needs, led to the redefinition of a number of the subdivisions of the science into independent disciplines. General microbiology deals with the fundamental principles of the biology of microorganisms. A knowledge of the basics of general biology is essential for work in any of the specialized branches of microbiology.
The content, scope, and problems of general microbiology have gradually changed. The objects once studied by microbiology included viruses, protists (the simplest plant or animal organisms), higher fungi, and algae; these are still described in foreign manuals of general microbiology. In the USSR, however, the study of these objects is not included under general microbiology.
Industrial microbiology includes the study and implementation of the microbiological processes used to obtain yeasts, fodder protein, lipids, and bacterial fertilizers and the production by microbiological synthesis of antibiotics, vitamins, enzymes, amino acids, nucleotides, and organic acids.
Agricultural microbiology deals with the composition of soil microflora, the role of microflora in the cycle of matter in the soil and in soil structure and fertility, the influence of cultivation on microbiological processes in the soil, and the effect of bacterial preparations on crop yields. Other areas of agricultural microbiology are the study and control of microorganisms that cause plant diseases and the development of microbiological methods of controlling insect pests of crops and timber and of preserving fodders, retting flax, and preventing the microbial spoilage of harvests.
Geological microbiology studies the role of microorganisms in the natural cycle of matter and in the formation and destruction of mineral deposits. It also proposes bacterial means of leaching metals from ores (copper, germanium, uranium, tin) and other minerals. Aquatic microbiology studies the quantitative and qualitative composition of the microflora of salt and fresh waters and the role of microflora in the biochemical processes occurring in water. It is also involved in monitoring the quality of drinking water and in making improvements in microbiological methods of sewage treatment.
Medical microbiology includes the study of the microorganisms that cause disease in man and the development of effective methods of controlling them. Veterinary microbiology deals with the same problems for agricultural and other animals.
The unique nature of viral structure and reproduction and the use of special methods of studying viruses have led to the development of virology as a science independent of microbiology.
Relation to other sciences. Microbiology is in some degree related to the following sciences: lower plants and animal morphology and taxonomy (mycology, algology, protistology), plant physiology, biochemistry, biophysics, genetics, evolutionary theory, molecular biology, organic chemistry, agricultural chemistry, soil science, biogeochemistry, hydrobiology, and chemical and microbiological technology.
Microorganisms are favored objects of research in studying general problems of biochemistry and genetics. For example, the mechanisms of formation of many natural compounds, such as the amino acids lysine and arginine, have been decoded with the aid of mutants that have lost the capacity to perform one of the stages of the biosynthesis of the substance in question. In order to reproduce the molecular nitrogen on an industrial scale, study of its fixation mechanism is directed at a search for catalysts analogous to those that under favorable conditions fix it in bacterial cells.
There is constant competition between chemistry and microbiology in the selection of the most economical means of synthesizing various organic substances. A number of substances that were once obtained microbiologically are now produced by purely chemical synthesis (ethyl and butyl alcohol, acetone, methionine, the antibiotic levomycetin). Certain syntheses are accomplished by both chemical and microbiological means (vitamin B2, lysine). In a number of cases, microbiological and chemical methods are combined (penicillin, steroid hormones, vitamin C). Finally, there are products and preparations that so far can be obtained only by microbiological synthesis (many antibiotics of complex structure, enzymes, lipids, fodder protein).
Modern microbiology. Both general microbiology and its specialized branches are developing extremely vigorously. There are three fundamental reasons for such development. First, microbiology has had the advantage of a large number of new methods of research, through advances made in physics, chemistry, and engineering. Second, the practical usefulness of microorganisms has increased sharply since the 1940’s. Third, microorganisms are being used to solve some of the most important theoretical problems of biology, such as heredity and variability, the biosynthesis of organic compounds, and metabolic regulation.
The successful development of microbiology is impossible without harmoniously combining studies on the populational, cellular, organic, and molecular levels. Cell-destroying equipment and gradient centrifugation (which makes it possible to obtain cell particles of different weights) are used to obtain acellular enzyme systems and fractions containing certain intracellular structures. New types of microscope technology have been developed to investigate microbial morphology and cytology. A method of capillary microscopy was invented in the USSR that has made possible the discovery of a new world of microorganisms, previously inaccessible to observation, with a unique morphology and physiology.
Various methods of chromatography and mass spectrometry, the method of isotope indicators, electrophoresis, and other physical and physicochemical methods have come into use for the study of microbial metabolism and chemical composition. Pure enzyme preparations are also used to detect organic compounds. New methods have been proposed for isolating and chemically purifying the products of the vital activities of microorganisms (adsorption and chromatography on ion-exchange resins; immunochemical methods based on the specific adsorption of a given product, such as an enzyme, by the antibodies that form after injection with the substance). The combination of cytological and biochemical methods of research has led to the development of a functional morphology of microorganisms. The electron microscope has made it possible to study the fine structural features, the composition, and the functions of the cytoplasmic membrane and ribosomes (for example, the role of the cytoplasmic membrane in transport or of the ribosomes in protein biosynthesis).
Laboratory research has been facilitated by fermenting chambers of various volume and design. The continuous method of culturing microorganisms, involving a constant supply of fresh nutrient medium and a constant efflux of the liquid culture, has become widespread. It has been established that in addition to cell reproduction (culture growth) there is culture development; that is, there are age-related changes in the cells making up the culture that are accompanied by physiological changes (even when reproducing intensively, young cells are incapable of synthesizing many metabolic products, such as acetone, butanol, and antibiotics, that can be formed by older cultures). Modern methods of studying the physiology and biochemistry of microorganisms have made it possible to establish the characteristics of their energy metabolism; the paths of biosynthesis of their amino acids, proteins, antibiotics, lipids, hormones, and other compounds; and the principles of their metabolic regulation.
Practical importance. Active participants in the natural cycle of matter, microorganisms play a most important role in soil fertility, in the productivity of bodies of water, and in the formation and destruction of mineral deposits. The capacity of microorganisms to mineralize the organic remains of animals and plants is especially important. The ever-increasing practical use of microorganisms has led to the development of the microbiological industry and to the substantial broadening of microbiological research in various branches of industry and agriculture. From the middle of the 19th century to the 1940’s, industrial microbiology principally studied various processes of fermentation, and microorganisms were used chiefly in the food-processing industry. Since the 1940’s, new trends, requiring different equipment design, have developed rapidly in industrial microbiology. For the first time, microorganisms were grown in large-capacity closed fermenting chambers. Methods have been perfected for separating the cells and isolating and chemically purifying their metabolic products from the culture fluid. Antibiotics were among the first of these products to be produced and developed industrially.
The following metabolic products are obtained on a large scale by microbiological methods: amino acids (lysine, glutamic acid, tryptophan), enzymes, vitamins, and nutritive yeasts on inedible raw material (caustic sulfite, hydrolysates of wood, peat, and vegetable by-products, petroleum and natural gas hydrocarbons, phenol- or starch-containing sewage). Polysaccharides are being produced by microbiological methods and lipids are being biosynthesized industrially.
The use of microorganisms in agriculture has grown dramatically. There has been an increase in the production of bacterial fertilizers, in particular, of nitragin from rhizobium cultures, which, in symbiosis with leguminous plants, fix nitrogen and are used to inoculate the seeds of leguminous crops. A new direction in agricultural microbiology is in the microbiological control of insects and their larvae—pests of crops and forests. Bacteria and fungi have been found whose toxins kill these pests, and the appropriate preparations are being produced. Desiccated cells of lactic-acid bacteria are used in the treatment of human and animal intestinal diseases.
The division of microorganisms into beneficial and harmful types is arbitrary, since the evaluation of the results of their activities depends on the conditions in which these results are manifested. For example, the microbial decomposition of cellulose is important and useful with plant remains or in the digestion of food (animals and humans being incapable of assimilating cellulose without preliminary hydrolysis by the microbial enzyme cellulase); on the other hand, the same microorganisms destroy fish nets, cables, cardboard, paper, books, and cotton fabrics. Microorganisms are grown on petroleum or natural gas hydrocarbons to obtain protein, but, on the other hand, they decompose and thereby destroy large quantities of petroleum and petroleum refinement products at oil fields and storage sites. Even pathogenic microorganisms cannot be called absolutely harmful, since vaccines are produced from them that protect against diseases.
Because of spoilage by microorganisms of plant and animal raw materials, food products, building and industrial materials, and manufactured goods, various methods of spoilage prevention have had to be devised (low temperatures, drying, sterilization, canning, the addition of antibiotics and preservatives, acidification). In other cases, it is necessary to accelerate the breakdown of certain chemical substances, such as pesticides in the soil. Microorganisms have a major role in the purification of sewage (the mineralization of matter contained therein).
Microbiologists are trained in the USSR in the microbiology subdepartments of universities, higher educational institutions of agriculture and food-processing, and medical and veterinary institutes. There are also special subdepartments for the microbiological industry. The All-Union Microbiological Society and the Society of Medical Microbiologists and Epidemiologists (membership, 17,000) also serve an educational function. The leading scientific institution in the field of general microbiology is the Institute of Microbiology of the Academy of Sciences of the USSR. The academies of sciences of many of the Union republics have created microbiological research institutes or divisions and have organized branch institutes and antibiotics institutes.
Works on various branches of microbiology are published in the journals Mikrobiologiia (Microbiology; since 1932), Zhurnal mikrobiologii, epidemiologii i immunobiologii (Journal of Microbiology, Epidemiology, and Immunobiology; since 1924), Prikladnaia biokhimiia i mikrobiologiia (Applied Biochemistry and Microbiology; since 1965), and Mikrobiologichnyi zhurnal (Microbiological Journal; Kiev, since 1934) and in Doklady AN SSSR (Reports of the Academy of Sciences of the USSR) and general biological journals. The annual Uspekhi mikrobiologii (Progress in Microbiology) has been published since 1964.
Foreign microbiological publications include Journal of Bacteriology (Baltimore, since 1916), Annual Review of Microbiology (Stanford, since 1947), Annales de Vlnstitut Pasteur (Paris, since \m\ArchivfurMikrobiologie (Berlin-Heidelberg, since 1930), and Zeitschriftfur allgemeine Mikrobiologie (Berlin, since 1960).
REFERENCESDostizheniia sovetskoi mikrobiologii. Moscow, 1959.
Frobisher, M. Osnovy mikrobiologii. Moscow, 1965. (Translated from English.)
Rabotnova, I. L. Obshchaia mikrobiologiia. Moscow, 1966.
Mikrobiologiia, 1967, vol. 36, issue 6. (”Sovetskaia mikrobiologiia za 50 let.”)
Meynell, G., and E. Meynell. Eksperimentarnaia mikrobiologiia. Moscow, 1967. (Translated from English.)
Schlegel, H. Obshchaia mikrobiologiia. Moscow, 1972. (Translated from German.)
A. A. IMSHENETSKII