by Lena VOROBYOVA, Dr. Sc. (Biol.), M. Lomonosov Moscow State University
Bacteria (microbes) are the first microscopic organisms that appeared here on earth. The biosphere and organic life-all that comes from them. Our very existence is inconceivable without them. Bacteria are implicated in the global turnover of substances, they are involved in soil formation, in the buildup and decomposition of mineral deposits. These microorganisms are widely used in the food, microbiological, chemical, medical and other industries.
More than three hundred years have passed since the Dutch naturalist Antony van Leeuwenhoek (1632 - 1723) discovered microbes. Up until then people had been living in blessed ignorance about the truly great role that bacteria are playing in sustaining the human race. Even today many do not suspect how fast organic life would have degraded in the absence of such microorganisms.
The total weight of the protoplasm (the living matter of every plant and animal cell) contained in microbes is all too large to be measured in practical terms. However, the quantitative aspect is not the main thing to prod scientists to peer into the microcosm of these tiny creatures. What counts above all are their peculiarities as manifest in the diversity of chemical activity, specificity of biochemical reactions, high rate of reproduction, intensity of metabolism (conversions) and other factors. Microbes are all-important in global problem solving, particularly, in what relates to the ongoing population explosion, environmental protection, food and energy...
Each and every microbe "specializes" in a particular area. Acting in concert, microbes are capable of converting, changing and upgrading as good as any organic matter. According to Dr. Sergei Vinogradsky (1856 - 1953), Corresponding Member of the St. Petersburg Academy of Sciences and one of the founders of the Russian school of microbiology, "microbes always turn up where they are needed" to provide for the "spontaneity and inevitability of this or that process at any point of the globe".
There is direct interdependence - if we take the interplanetary level-between green plants that effect photosynthesis and bacteria that process organic matter. This is a perennial process: every year the land surface of our planet gets covered with fallen leaves, broken twigs and branches of trees, and so forth; and every spring all this rubbish is eliminated by scavenger microbes that decompose and oxidize the compound molecules of the dead litter. And thus as much as 200 billion tons of carbon dioxide (CO2 ) is formed. Assimilated by green plants, this gas is converted to
Carbon turnover in nature. Carbon is bound by photo - and chemoautotrophic microorganisms. Aerobic processes are indicated by blue arrows, and anaerobic - by red ones.
Microbial kingdom in soil.
free oxygen (O2 ) of which about 145 bn tons is released into the atmosphere. Unless replenished regularly, the pool of both gases would have run out within 30 years or so. It is thanks to photosynthesis that more than 100 bn tons of organic matter is produced every year.
Bacteria have thus a crucial role to play in the universal rotation of substances, and herein lies their global significance. They are "working" here, there and everywhere - in soil, in lakes and rivers, in seas and oceans. Some of them decontaminate water, and stabilize the acidity of the ambient environment; they stabilize the present-day atmosphere, too.
Simultaneously, microbes act as a go-between to unify all biological systems on the globe. Due to their tiny size their cell genome happens to be deficient, and therefore their cell is restricted in its metabolic potential but can make it up by interacting with other bacteria. For instance, in contrast to eukaryotes*, prokaryotes** have a joint pool (reserve) of genes and, if necessary, pass the useful genes to other cells. Complementing one another, bacteria combine into a planetary community, a superorganism of sorts, comparable to a powerful computer network.
Wild animals, migratory birds, fish and insects amplify it many times over. Dr. Zorin Zonea of Canada says this biological communication network contains more information in it than does the brain of any mammalian, and it operates in a mode similar to intelligence now and then. Man, the Homo sapiens, will keep only things he needs in this or that particular situation. Bacteria, however, carry miniature replicons (chromosome duplicates), and these have a "kit of tools" of their own.
Yet another analogy, one related to the mode of information exchange, suggests itself here. Say, human beings share their life experience and knowledge with offspring and also with friends, acquaintances, and neighbors. Bacteria act in much the
* Eukaryotes (Eukaryotic cell; Eukaryocyte) - organisms with cells that have a discrete membrane (karyomembrane) to the nucleus, enclosing the genetic material. - Ed.
** Prokaryotes (Prokaryotic cell; Prokaryocyte)-organisms with cells appearing to be without a discrete nuclear membrane enclosing the genetic material. Bacteria and blue-green algae are prokaryote organisms. - Ed.
Soil bacteria. The photo is made under a fluorescent microscope upon the staining of cells (shown in pink) with fluorescent dye.
same way. They convey their genes not only to filial cells during reproduction via division or budding, but also to cells of nonallied species. Hence their countless numbers: one gram of soil carries up to ten billion microbes; one hectare (2.5 acres) of soil has 1700 kg of bacteria in it, about 1700 kg of microscopic fungi and 170 kg of protozoa (according to the RAS Institute of Soil Science). A pinch of soil is populated by so many microorganisms equal in number to the entire human population of the globe.
Filamentous bacteria (actinomyces or actinomycates) are playing an important role in attacking such substrates as hydrocarbons, plant tissues, and humus. Some of them can destroy pesticides as well. We know of bacteria that produce iron and phosphorus compounds in forms readily consumed by plants. Some microorganisms synthesize vitamins and phytohormones activating the growth of the green mass. Incidentally, the smell of soil so much familiar to all of us comes from geosmine, a volatile substance released by actinomyces (actinomycates).
In addition to all that bacteria can bind atmospheric nitrogen in a form readily assimilated by plants. Nitrogen compounds, so vital to biological processes, occur but in very small amounts in soil, and much of this bound nitrogen is carried away with harvested crops every autumn, or else washed off by rain and destroyed in bacterial denitrification*.
The nitrogen binding process occurs via two pathways. First, through spontaneous fixation of atmospheric nitrogen by means of electric discharges during thunderstorms when the intensity of lightning may be as high as 200 mn kW, with the air temperature in the flash-point rising to 20,000 degrees centigrade. Under like conditions nitrogen and oxygen molecules break into constituent atoms interacting with one another and producing NO (nitrogen monoxide) which, in turn, is oxidized to nitrogen dioxide (NO2 ); and this one, taking in water molecules, turns into nitric acid (HNO3 ) which gets into the ground with rainfall.
Second, there is also biological fixation of atmospheric nitrogen through nitrogenase, an enzyme present in microbes. Plants get the nitrogen product from them, and it protects all living creatures in the end. For example, certain leguminous plants and bacteria co-existing in one of the best-known forms of symbiosis give off substances conducive to bacterial colonization of root hairs and formation of tubercles. The yield of farm crops infected with tubercular bacteria is up by 25 to 30 percent. In 2003 the Department of Ecological Biotechnology (Federal Administration of Medico-Biological Problems, RF Health Ministry) developed a technique for obtaining a fertilizer on the basis of biohumus and hay bacillus. This is achieved by composting
* Denitrification - biological decomposition of nitrogen compounds whereby free nitrogen is liberated; as a result, the fertility of soil declines because of the lower amount of bound nitrogen in it. - Ed.
Tubercles on clover root hairs.
farm wastes (cattle manure, hard matter from effluents) with the involvement of a special race of earthworms. Thereby soil fertility is boosted manifold.
Bacteria not only ameliorate soil and enrich it with useful substances - they protect crops against pests as well. Many countries the world over are spending huge funds for the production of pesticides. But these agents have a major drawback-they are toxic for useful insects, birds, fish and animals-and for man, too. It has become possible to avoid the massive use of toxic chemicals by developing bioinsecticidal preparations from bacterial cells and metabolites-preparations targeted exclusively at farm pests but ecologically friendly at the same time.
It was Ilya Mechnikov (honorary member of the St. Petersburg Academy of Sciences since 1902) who back in 1883 discovered the ability of microorganisms to kill harmful insects. He turned attention to a dying fly covered with a white patch that came from a microscopic fungus. The scientist checked the insecticidal action on beet crops. Beet plants growing on the experimental plot yielded a good harvest of sound vegetables, while one control plant and tubers alike were larva-eaten all through.
Used world-wide now are about 50 preparations developed from microbial cells and metabolites, effective against 160 species of pests, including the Colorado potato beetle, apple worm, cotton cutworm, and pests destroying Indian corn and other crops. Most of the preparations are obtained from the spore bacterium Bacillus thuringiensis. Here in Russia we are producing more than ten varieties: entobacteria (Institute of Microbiological Means of Plant Protection and Bacterial Preparations, Moscow), dendrobacillin - against Siberian silkworm (Institute of Microbiology, Irkutsk), bitoxibacillin - against farm crop pests (Institute of Agricultural Microbiology, St. Petersburg), to name but a few. The intracellular proteic protox - in swallowed by an injurious insect is dissolved in the alkaline medium of its intestine and turns into a toxic substance. The thus infected pest dies within a few days.
Yet another essential characteristics: microorganisms can enter into various symbiotic associations. We at the Microbiology Chair (Department of Biology, Moscow State University) have found that bacterial cells (those of propionic bacteria in particular) can under definite conditions exude nucleoproteic substances, presumably of the sensory type, contributing to their own survival and also sustaining the survival of nonallied forms of microbes and even yeast under stress.
Tubercles formed by RHIZOBIUM on the stem of a tropical leguminous plant.
Such kind of solidarity is particularly evident in bacterial communities colonizing the alimentary tract of mammals, say, ruminants. These get a fodder mix as a rule, which contains much cellulose but little of the proteins and lipids. Yet billions of microbes populating the bowels of the host act on this mixture and, in a matter of hours, produce glucose, cellobiose and other beneficial compounds. In certain segments of the stomach and intestine, bacteria and protozoa are digested by enzymes to produce ammonium, urea, amino acids, vitamins and other substances so much needed for well-balanced nutrition.
Human life is like was unthinkable in the absence of bacteria. They inhabit the human organism from the moment of birth up until demise. The gastrointestinal tract of adult humans teems with more than 500 different microbial species with a total mass of over 1 kg (more than two pounds). Bacteria form a biofilm covering man's skin and mucous membranes. This film regulates relationships between the host organism (macroorganism) and the ambient environment, and it also regulates the activity of the central nervous, endocrine and immune systems.
A disbalance of this system may result in grave diseases. Many antimicrobial substances, antibiotics especially, prescribed by doctors can suppress the normal sensitive microflora, something that inevitably leads to dysbacteriosis. The all-round studies into the phenomenon, carried out at the Moscow-based G. N. Gabrichevsky Institute of Epidemiology and Microbiology, provide for rehabilitation of the microflora with the help of probiotics developed on the basis of bifid and lactic-acid bacteria. The State Research Center of Virology and Biotechnology (RF Health Ministry) is cloning interferon genes on a live probiotic bacterium which are administered peros (perorally) to protect a patient against the degrading action of mucosal enzymes. Interferon genes cultivated this way possess antiviral, immunomodulating and anti-tumor characteristics, and keep up the antibiotic activity of the probiotic strain.
We could cite many other examples, too, when scientists act as lords of bacteria and make them do something not proper to them but useful to man. The Sintez ("Synthesis") enterprise in the town of Kurgan produces vitamin B12 from a mutant strain of propionic-acid bacteria.* Using certain genetic manipulations, microbiologists have achieved a 5,000 fold increase in the output of the vitamin. Bacterial leavens and ferments have found wide use in baking, in sausage production, in the milk and dairy industry (cheese-processing, sour milk products), food vinegar production, in preservatives, feed siloing, and so forth.
* See: L. Vorobyova, "Propionic-Acid Bacteria", Science in Russia, No. 2, 2002. - Ed.
A pest caterpillar before (a) and three days after bioinsecticidal treatment (b).
Or take the matter of the limited power resources on our planet, much on the mind of many people.
In this connection a team of Moscow University experts, among them Acad. Yelena Kondratyeva and Prof. Ivan Gogotov, came up - back in the 1980s - with the idea of obtaining an extra pure fuel, molecular hydrogen, in the microbiological technique of biophotolysis, or the photodecomposition (decomposition in light) of water (H2 O) into its constituent parts, hydrogen (H2 ) and oxygen (O2 ). This is done by the cyanobacteria Anabaena cylindrica under nitrogen starvation conditions. As much as 1000 kW-h of hydrogen can be produced monthly in a shop 7 m2 large and 1 m tall. As H2 producer the phototrophic extreme halophilic archaeota Halobacterium salinarium can be employed. Their bacteriorhodopsin, which is implicated in the extrusion of protons from the cell, is durable and quite resistant to mechanical impacts, acids, alkalis, oxidizers and other stressors.
In their turn, the anaerobic Rhodospirillum rubrum responsible for photosynthesis can convert certain organic substance into H2 and CO2 in the absence of nitrogen and under illumination. Accordingly, one is weighing the possibility of obtaining molecular hydrogen in the process of waste disposal, the way it is done in the production of methane with the use of methanogenic archaeota.*
It is also planned to use the symbiosis of tubercular bacteria in plants whereby hydrogen is "extruded" from tubercles, with nitrogen diffusing into root hairs. The Agrobacterium tumefaciens ("a tumor - inducing" bacterium) contains a Ti-plasmid which, if injected into plant cells, causes large tumors, the crown galls so-cabled. This plasmid could be impregnated with nif (nitrogenase) genes. Traveling, e.g., in tree cells, the implant will induce gall formation all through the tree trunk. The galls, consuming a large amount of photosynthates (sugars), will release hydrogen which could be collected in plastic tubes under low pressure and feed into a large receptacle. This setup is capable of reaching a capacity of 1 W/m2 . Looks fantastic? But this is only one example to show the trends of scientific and technological progress in this twenty-first century.
* See: L. Vorobyova, "This Wonderworld of Archaeota", Science in Russia, No. 5, 2004. - Ed.
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