[Monitoring of the chitinolytic microbial complex of the phylloplane]

A comprehensive study of chitinolytic microbial complexes of the phylloplane from cultured and forest plants has been conducted. An increase of the number and biomass of metabolically active cells of the representatives of the domain Bacteria and a decrease in fungal biomass in the experimental microcosms have been shown to occur after the introduction of chitin. The characteristic features of the taxonomic structure of metabolically active chitinolytic complexes of the phylloplane of the plants studied have been elucidated. Representatives of the phyla Proteobacteria, Bacteroidetes, and Verrucomicrobia have been shown to play important roles in the chitinolytic complexes of green leaf samples, while mycelial actinobacteria of the phylum Actinobacyteria played a similar role in needles of coniferous trees. A collection of chitinolytic microorganism cultures isolated from the phylloplane of different plant species has been created.

[Sizes of bacterial cells in soils determined by cascade filtration technique]

This paper studies the number of bacteria in typical chernozem and mountain-meadow soil by the traditional method and the cascade filtration technique. The total number of bacteria in these soils, which was obtained in filters of different diameters during filtering the suspension of a certain amount, is 1.5-5 times higher than that obtained by the traditional method. In the structure of the bacterial biomass in both soils, the biomass of bacterial cells with a diameter of 0.38-0.43 microm was dominating by 8-90%. In the typical chernozem, the biomass of cells with a diameter of 0.17 microm was slightly more than 1%; in the mountain-meadow soil, the percentage of the biomass of cells with a diameter of 0.17 microm increased by 5%. The average volume and diameter of the bacteria in the studied soils were calculated. In typical chernozem, the average volume of bacterial cells was equal to 0.0046 microm3 and the diameter was 0.206 microm. In the mountain-meadow soils, these values were slightly lower, 0.0038 microm3 and 0.194 microm, respectively. The biomass of the bacterial cells, which is usually calculated based on the cell volume of 0.1 microm3, is overestimated by about five times when counting the number on the filters. The percentage of the real biomass of soil bacteria is traditionally much lower than that estimated.

[Temperature as a factor of development of psychrotolerant mycelial bacteria complexes in soils of north regions]

It has been demonstrated that complexes of mycelial bacteria (actinomycetes), in which the amount of psychrotolerant actinomycetes reaches hundreds of thousands of CFU/g of the soil (frequently exceeding the portion of mesophilic forms), are developed in peat and podzolic soils of the tundra and taiga at low temperatures. As actinomycetes grow and develop in cold soils, their mycelium increases in length. Use of the molecular in situ hybridization method (fluorescent in situ hybridization, FISH) demonstrated that the portion of metabolically active mycelial actinobacteria exceeds the portion of unicellular actinobacteria in the Actinobacteria phylum. Specific peculiarities of psychrotolerant populations in relation to the spectrum of consumed substrates (histidine, mannitol, saccharose) were established by the method of multirespirometric testing.

[Anaerobic growth ability and alcohol fermentation activity of microscopic fungi]

The method proposed in this study was used to isolate fungi grown under anaerobic conditions and to reveal distinctions in their abundance and species composition in different habitats. The ability of micromycetes of different taxa to grow under anaerobic conditions and ensure alcohol fermentation was determined for a representative sample (344 strains belonging to more than 60 species). The group of fungi growing under anaerobic conditions included species with high, moderate, and low fermentation activity. The ability for anaerobic growth and fermentation depended on the taxonomic affiliation of fungi. In some cases, the expression of these characteristics depended on the habitat from which the strain was isolated. The maximum level of ethanol accumulation in culture liquid (1.2-4.7%) was detected for Absidia spinosa, Aspergillus sp. of group flavus, Aspergillus terreus, Acremonium sp., Mucor circinelloides, Mucor sp., Fusarium oxysporum, F. solani, F. sambucinum, Rhizopus arrhizus var. Arrhizus, Trichoderma atroviride, and Trichoderma sp.

[Fungal to bacterial biomass ratio in the forest soil profile]

The carbon content in microbial biomass (Cmic-BM) was determined in various horizons of the soil profile (sod-podzo, gray, podzol, and rzhavozem) of various forests (oak, spruce Yellow Archangel, spruce moss, aspen, spruce broadleaf) in the southern taiga of European Russia (Moscow and Kaluga oblasts) by the substrate induced respiration (SIR) and direct microscopy (DM) methods. The fungi-to-bacteria ratio was measured by the selective inhibition technique and DM. A quantitative differentiation of the fungal mycelium was suggested. The Cmic-DM/Cmic-SIR in various horizons of the soil profile was about 98%. The fungal contribution to MB was 52-74% and 92-99% according to the SIR and DM data, respectively. The microbial parameters were associated with the CO2 and N2O production by the soils. The contradictory data about the fungi proportion in the MB of soils of various ecosystems were discussed.

[Definition of the physiological condition of bacteria in soil by means of luminescent dye L7012]

By means of dye L7012, the number and physiological condition (damage rate of membranes) of bacterial cells is defined. The results testify to considerable physiological heterogeneity of bacteria cells in soils. In fresh samples of soil, the percentage of intact cells reached 60-70%. Damaged membranes occurred in 30-40% of cells. The number of damaged cells dramatically increased downwards through the soil profile. Drying and freezing of soil samples considerably reduced the quantity of intact cells and increased the percentage of cells with damaged membranes; the number of intact cells was 10-20%. Treatment with biocide agents resulted in lysis of the majority of cells and cells injuries. However, some of the cells kept an intact cellular membrane, which testifies to the high stability of bacteria in soil. These data allow us to offer a method of staining a soil suspension with the use of luminescent dye L7012 with the quality of an express method that gives the chance to monitor the number and physiological condition of the bacterial complex of soils.

[Estimation of abundance dynamics of gram-negative bacteria in soil]

Bacterial succession in soil was studied for two variants of initiation (moistening and moistening with addition of glucose). To determine the numbers of viable gram-negative bacteria, the modified nalidixic acid method was applied. The numbers of gram-negative bacteria revealed by this method were 2 to 3.5 times higher than those determined by the traditional method. In a developing community, the highest total bacterial numbers were observed on day 7; afterwards their numbers decreased and stabilized at a level exceeding four- to fivefold the initial one. In both experimental variants, the highest numbers of viable gram-negative bacteria were revealed on day 15 (75-85% of the total bacterial numbers). Morphology of these bacteria suggests their classification as cytophagas (chitinophagas) utilizing chitin from the dead fungal mycelium.

[Comparative assessment of soil microbial biomass determined by the methods of direct microscopy and substrate-induced respiration]

The content of microbial biomass (MB) was determined in samples of gray forest, chestnut, and tundra soils with different physicochemical properties (0.4-22.7% Corg; 8.4-26.8% silt particles; pH 4.3-8.4) by the methods of substrate-induced respiration (MB(SIR)) and direct microscopy (MB(M)). The samples of two upper soil layers, 0-5 and 5-10 cm (without plant litter), from different ecosystems (forest, forest shelter belt, meadow, fallow, and arable land) and elements of relief of interfluvial tundra (block/upper land plateau, depression between blocks) have been analyzed. The content of microbial biomass in the 0-5-cm soil layer was 216-8134 and 348-7513 microg C/g soil as measured by the methods of substrate-induced respiration and direct microscopy, respectively. The MB(SIR) and MB(M) values closely correlated with each other: r = 0.90 and 0.74 for 0-5 and 5-10 cm, respectively. The average MB(SIR)/MB(M) ratio was 90 and 60% for 0-5 and 5-10 cm, respectively. The portion of microbial carbon in total organic soil carbon was, on average, 4 and 3% (SIR) and 5 and 7% (direct microscopy) for 0-5 and 5-10 cm, respectively. Possible reasons for the differences between MB(SIR) and MB(M) values in the soils under study are discussed.

[Diversity of facultatively anaerobic microscopic mycelial fungi in soils]

The numbers of microscopic fungi isolated from soil samples after anaerobic incubation varied from tens to several hundreds of CFU per one gram of soil; a total of 30 species was found. This group is composed primarily of mitotic fungi of the ascomycete affinity belonging to the orders Hypocreales (Fusarium solani, F. oxysporum, Fusarium sp., Clonostachys grammicospora, C. rosea. Acremonium sp., Gliocladium penicilloides, Trichoderma aureoviride, T. harzianum, T. polysporum, T. viride. T. koningii, Lecanicillum lecanii, and Tolypocladium inflatum) and Eurotiales (Aspergillus terreus, A. niger, and Paecilomyces lilacimus), as well as to the phylum Zygomycota, to the order Mucorales (Actinomucor elegans, Absidia glauca, Mucor circinelloides, M. hiemalis, M. racemosus, Mucor sp., Rhizopus oryzae, Zygorrhynchus moelleri, Z. heterogamus, and Umbelopsis isabellina) and the order Mortierellales (Mortierella sp.). As much as 10-30% of the total amount of fungal mycelium remains viable for a long time (one month) under anaerobic conditions.

[Abundance, biomass, structure, and activity of the microbial complexes of minerotrophic and ombrotrophic peatlands]

Very large microbial biomass was revealed in peat bogs by means of fluorescence microscopy. In ombrotrophic peatlands, the pool of the dry-weight microbial biomass in the 1.5-m layer constituted 3-4 t/ha and was twice as high as in the minerotrophic peat bogs. Fungal biomass was predominant (55-99%) in ombrotrophic peatlands, while bacterial biomass predominated in minerotrophic peatlands (55-86%). In ombrotrophic peatlands, the microbial biomass was concentrated in the upper layers, while in minerotrophic peatlands, it was uniformly distributed in the bulk. After drainage, the microbial pool in the ombrotrophic peatlands increased twofold; that in the minerotrophic peatlands remained at the same level. The potential activity of nitrogen fixation and denitrification was revealed across the whole profile of the peatlands. The average values of these potential activities were five times higher in the minerotrophic peatlands, where bacterial biomass predominated.

[The composition of the chitinolytic microbial complex and its effect on chitin decomposition at various humidity levels]

The dynamics of assimilation of chitin by soil microorganisms (primarily prokaryotes) as a source of carbon and nitrogen has been determined by gas chromatography and fluorescence microscopy. The highest rates of chitin decomposition in chernozem were detected at humidity levels corresponding to the pressure of soil moisture (P) of -1.4 atm. The rate of microbial consumption of chitin is three times higher than that of the carbon of soil organic matter. Fluorescence microscopy revealed that an increase in the pressure of soil moisture from P = -10 atm to P = -0.7 atm resulted in a considerable increase in the proportion of the specific surface of mycelial bacteria (actinomycetes).

[Haloalkaliphilic actinomycetes in soils of Mongolian desert steppes]

The abundance of actinomycetes isolated from the soils of Mongolian desert steppes varies from several thousand to hundreds of thousands of CFU/g soil, depending on soil type and isolation medium. Eight actinomycete genera have been found in these soils: Streptomyces, Micromonospora, Saccharopolyspora, Actinomadura, Microtetraspora, Thermomonospora, Nocardia, and Dactylosporangium. The streptomycete complexes of brown desert-steppe and gray-brown desert alkaline soils include halophilic, alkaliphilic, and haloalkaliphilic species that grow most successfully on the media with a salt concentration of 5% and pH 8-9.

[Actinomycete growth in conditions of low moisture]

Actinomycete communities demonstrated a replacement of the generic composition in time as a function of soil moisture. Representatives of the genera Streptomyces, Micromonospora, Actinomadura, Saccharopolyspora, and Microbispora were repeatedly isolated from soil under different moisture conditions (field capacity, maximum molecular capacity, and maximum adsorption capacity). Representatives of some rare genera (Thermomonospora and Kibdelosporangium) were isolated from soil with low moisture levels inhibiting growth of more hydrophilic actinomycetes and bacteria. Spores of some actinomycetes could grow at low relative air humidity (RH) (50 and 67%). The complete growth cycle of all actinomycetes starting from spore germination to sporulation was observed only at RH of 98%.

[Lignite microorganisms]

The first demonstration that samples of lignite at a depth of 10 m are considerably enriched in bacteria is reported. According to direct microscopy, the abundance of bacteria was about 10(7) cells/g. About 70% of cells had intact cell membranes and small size, which points to their anabiotic state. The fungal mycelium length was no more than 1 m. Lignite inoculation onto solid glucose-yeast-peptone medium allowed as to isolate bacteria of the genera Bacillus, Rhodococcus, Arthrobacter, Micrococcus, Spirillum, and Cytophaga. Representatives of the genera Penicillium and Trichoderma were identified on Czapek medium. Moistening of lignite powder increased the microbial respiration rate and microbial and fungal abundance but did not increase their generic diversity. This finding suggests that the studied microorganisms are autochthonous to lignite.

[Reaction of microorganisms to the digestive fluid of the earthworms]

The reaction of soil bacteria and fungi to the digestive fluid of the earthworm Aporrectodea caliginosa was studied. The fluid was obtained by centrifugation of the native enzymes of the digestive tract. The inhibition of growth of certain bacteria, spores, and fungal hyphae under the effect of extracts from the anterior and middle sections of the digestive tract of A. caliginosa was discovered for the first time. In bacteria, microcolony formation was inhibited as early as 20-30 s after the application of the gut extracts, which may indicate the nonenzymatic nature of the effect. The digestive fluid exhibited the same microbicidal activity whether the earthworms were feeding on soil or sterile sand. This indicates that the microbicidal agents are formed within the earthworm's body, rather than by soil microorganisms. The effect of the digestive fluid from the anterior and middle divisions is selective in relation to different microorganisms. Of 42 strains of soil bacteria, seven were susceptible to the microbicidal action of the fluid (Alcaligenes.faecalis 345-1, Microbacterium sp. 423-1, Arthrobacter sp. 430-1, Bacillus megaterium 401-1, B. megaterium 413-1, Kluyvera ascorbata 301-1, Pseudomonas reactans 387-2). The remaining bacteria did not die in the digestive fluid. Of 13 micromycetes, the digestive fluid inhibited spore germination in Aspergillus terreus and Paecilomyces lilacinus and the growth of hyphae in Trichoderma harzianum and Penicillium decumbens. The digestive fluid stimulated spore germination in Alternaria alternata and the growth of hyphae in Penicillium chrysogenum. The reaction of the remaining micromycetes was neutral. The gut fluid from the posterior division of the abdominal tract did not possess microbicidal activity. No relation was found between the reaction of microorganisms to the effects of the digestive fluid and the taxonomic position of the microorganisms. The effects revealed are similar to those shown earlier for millipedes and wood lice in the following parameters: quick action of the digestive fluid on microorganisms, and the selectivity of the action on microorganisms revealed at the strain level. The selective effect of the digestive gut fluid of the earthworms on soil microorganisms is important for animal feeding, maintaining the homeostasis of the gut microbial community, and the formation of microbial communities in soils.

[Microbial transformation of chitin in soil under anaerobic conditions]

Anaerobic chitinolytic complex was studied in three soil types: chernozem, gray forest soil, and chestnut soil. The abundance and biomass of anaerobic chitinolytic microbial complex of fungi, bacteria, and actinomycetes were evaluated by luminescent microscopy. The dynamics of methane emission from soil during chitinolytic succession was studied by gas chromatography. All three studied microbial groups proved to participate in chitin transformation in soil under anaerobic conditions. The highest biomass growth was observed among prokaryotes, particularly actinomycetes, whose biomass doubled. The increase in methane emission during chitinolytic succession was most pronounced in soils with low organic matter content.

[Spore germination and mycelial growth of streptomycetes at different humidity levels]

This study is the first to show the ability of streptomycetes to develop at a very low humidity level. All of the streptomycetes studied produced growth at low humidity (aw 0.86 and 0.67). This capacity was most markedly pronounced in Streptomyces odorifer, whose spores were capable of germinating, and mycelial germs increased in length, at the air humidity aw 0.50. The formation of lateral branches (mycelium branching) at this humidity was noted only in single S. odorifer germs and only after 72 h of incubation. Study of streptomycete growth on an agarized medium with different osmotic pressures, created by various glycerol concentrations in the medium, showed that, at aw 0.67, the spores of all the streptomycetes studied germinate, producing mycelial germs but not microcolonies. The ecological significance of mycelial prokaryotes in soil microbial communities that develop and function under conditions of extremely low humidity is discussed.

[Alkaliphilic soil actinomycetes]

The actinomycete complex of alkaline soils was found to be dominated by alkaliphilic streptomycetes, which showed maximal radial rates of colony growth at pH 8. At pH values of 7 and 10, the growth of these streptomycetes was poor. Alkaliphilic streptomycetes can be morphologically differentiated from other actinomycetes based on their high radial rates of colony growth and increased spore formation in alkaline media as compared to neutral media.

[The saprotrophic bacterial complex in the raised peat bogs of Western Siberia]

The population density of bacteria in peat deposits along the landscape profile of the Vasyugan Marsh has been found to be as high as tens of millions of CFU/g peat. The abundance and diversity of bacteria increased with depth within the peat deposit, correlating with an increasing level of peat degradation. Variations in these parameters with depth and season were greater in peat deposits located in transaccumulative and transitional positions than in the sedge-sphagnum bogs located at the eluvial region of the profile. In the upper 1-m-thick layer of the peat deposits studied, bacilli, represented by five species, dominated, whereas, in the deeper layers, spirilla and myxobacteria prevailed. These bacteria were major degraders of plant polymers. Unlike the bacterial communities found in the peat deposits of European Russia, the dominant taxa in the studied peat deposits of Western Siberia are represented by bacteria resistant to extreme conditions.

[Autoregulation of conidium germination in micromycetes of the genus Trichoderma]

The amount of germinated conidia of microcytes belonging to the genus Trichoderma considerably decreased with an increase in the population density. Strains exhibited different ecological strategies. The maximum number of germinated conidia (30-70%) was recorded when the average distance between conidia was 50 microns.

[Growth and morphological differentiation of acidophilic and neutrophilic soil streptomyces]

Acidophilic actinomycetes are shown to possess a special mechanism of adaptation to low pH conditions, which shows up in their ability to grow faster on acidified than on neutral media and to adjust the pH of the medium to a level favorable for the formation of aerial mycelium and spores. On nutrient media with pH below 5, neutrophilic actinomycetes either fail to grow or grow much slower than on neutral media; they do not alkalize the medium and do not form aerial mycelium.

[The quantity and structure of the root-associated microbial complexes of two greenhouse rose cultivars]

The study of the root-associated microbial complexes of affected and healthy rose plants of two cultivars (Grand gala and Royal velvet) grown in a greenhouse showed that the biomass of eukaryotic microorganisms in the rhizoplane and rhizosphere of healthy rose plants and in the surrounding soil was considerably lower than in the same loci of affected plants. In contrast, the biomass of root-associated prokaryotic microorganisms was higher in the case of healthy than in the case of affected rose plants. The root-associated bacterial complexes of both affected and healthy rose plants were dominated by the genera Arthrobacter, Rhodococcus, and Myxobacterium and did not contain phytopathogenic bacteria. The root-associated fungal complex of healthy roses was dominated by fungi of the genus Trichoderma, whereas that of the affected rose plants was dominated by the species Aureobasidium microstictum. The affected cane cuttings and cankers occurring on affected canes were found to contain Coniothyrium fuckelii (the causal fungus of rose stem canker) and sclerotia of Botrytis cinerea (the causal fungus of gray rot). The micromycete complex of healthy rose plants was not so diverse as was the micromycete complex of affected rose plants.

[The biometric analysis of bacteria in soil]

The biometric analysis of bacterial cells in soil by light, fluorescence, and scanning electron microscopy showed that their average size is 0.8 micron in diameter, 1.4 microns in length, and 0.7 micron 3 in volume. In soil loci with enhanced microbiological activity (the rhizoplane of plants and the intestinal tract of soil invertebrates), the average size of bacterial cells was found to be 40% smaller than that of cells occurring in other parts of soil. It is the first experimental evidence showing that the metabolic activity of soil bacteria and their concentration and allometric parameters are related.

[Selective isolation of actinomycetes of the genus Actinomadura from soil]

Some approaches to the selective isolation of actinomycetes of the genus Actinomadura from soil are described. The approach that involves thermal treatment of soil samples and their plating onto Gauze 1 medium with the antibiotics nystatin, nalidixic acid, and rubomycin provides for an increased amount of actinomaduras isolated from the soil actinomycete complex and for a decreased amount of streptomycetes.

[New criteria for evaluation of soil bacterial complexes]

The initial concentration of prokaryotic microorganisms, the type of their growth, doubling time, and the growth dynamics of bacteria and actinomycetes in three types of soil (meadow, chestnut, and soddy forest) were evaluated by the luminescence microscopic analysis of soil samples incubated in a humid chamber for 1 day. Soddy forest and chestnut soils differed in most of the parameters analyzed. Meadow soil was close to soddy forest soil in some parameters and to chestnut soil in other parameters. All soil suspensions exhibited high growth rates of bacteria and actinomycetes, indicating that the fraction of viable microorganisms in the soils was high.

[Actinomycetes of the genus Micromonospora in meadow ecosystems]

Investigations showed that micromonosporas, along with streptomycetes, are the major inhabitants of floodplain meadow ecosystems, where their population varies from tens of thousands to hundreds of thousands of CFU per g substrate. In spring, the population of micromonosporas in soil and on the plant roots was found to be denser than that of streptomycetes.

[Actinomycetes in the rhizosphere of barley plants grown in the strongly acidic soddy podzolic soil]

The study of various factors (soil acidity, the variety of barley plants, and their developmental phases) on the rhizosphere actinomycete complex showed that it is soil acidity that substantially influences the population of rhizosphere actinomycetes. The effect of soil acidity was most likely due to the different tolerance of rhizosphere actinomycetes to high concentrations of the aluminum and hydrogen ions. The developmental phases of barley plants correlated with the population indices of only one genus of actinomycetes, Micromonospora.

[Acidophilic soil actinomycetes]

A clear-cut dependence of the distribution of acidophilic actinomycetes on the pH value of soil was established. Acidophilic actinomycetes were found to be present in soils whose pH does not exceed 6.8 (acid forest soils, lowland peaty soil, and ordinary chernozem) and not in slightly alkaline soils (chestnut sodic and alluvial meadow soils). In the acid lowland peaty soil, the species diversity of acidophilic streptomycetes was lesser than the species diversity of streptomycetes revealed in the same soil by using neutral medium.

[Tolerance of soil bacterial complexes to salt shock]

Investigations showed that bacteria present in soil are resistant to one-day exposure to a saturated solution of ammonium nitrate and can well develop when transferred to laboratory nutrient media. The evaluated number of bacteria in NH4NO3-treated soil samples was nearly the same as in native soil samples, while was 1.5-2.5 times smaller in the former than in the latter case when microbial succession in the soil samples was initiated by wetting them. Bacteria (particularly gram-negative ones) occurring at the early stages of succession were the most sensitive to salt stress. Bacteria in soil were found to be much more resistant to salt stress than the same bacteria isolated in pure cultures.

[The growth-promoting effect of Beijerinckia and Clostridium sp. cultures on some agricultural crops]

New strains of Beijerinckia mobilis and Clostridium sp. isolated from the pea rhizosphere were studied with respect to their promoting effect on the growth and development of some agricultural crops. Seed soaking in bacterial suspensions followed by the soil application of the suspensions or their application by means of foliar spraying was found to be the most efficient method of bacterization. The application of B. mobilis and Clostridium sp. cultures in combination with mineral fertilizers increased the crop production by 1.5-2.5 times. The study of the population dynamics of B. mobilis by the method of genetic marking showed that this bacterium quickly colonized the rhizoplane of plants and, therefore, had characteristics of an r-strategist. At the same time, Clostridium sp. was closer to K-strategists, since this bacterium slowly colonized the econiches studied. The introduction of the bacteria into soil did not affect the indigenous soil bacterial complex. The presence of Clostridium sp. slowed down the colonization of roots by the fungal mycelium. The possible mechanisms of the plant growth-promoting activity of B. mobilis and Clostridium sp. are discussed.

[Bacterial diversity in microcosms of soils with various humidity]

The succession analysis of bacterial diversity in the A horizons (rich in organic matter) of three contrasting types of soil--burozem, soddy gley soil, and chernozem--showed that the bacterial diversity of soil microcosms in humid regions can be adequately evaluated only if soil samples are incubated at different soil moisture contents. A complete account of actinobacteria and proteobacteria requires the levels of soil moisture corresponding to the maximum capillary-sorption moisture and capillary moisture, respectively. The bacterial diversity, whose value was maximum on the 40th day of succession, was higher in soddy gley soil than in burozem. The taxonomic structures of the bacterial communities of these two types of soil were different. After wetting chernozem samples from arid regions, the soil bacterial community changed insignificantly with time and drastically differed from that of soils from humid regions. The difference in the bacterial diversity of soils was the most distinct when it was evaluated by measuring the proportion between proteobacteria and actino-bacteria.

[Structure of bacterial complexes of the river Protva flood-plains]

The synecological analysis of bacterial communities from the Protva River flood-plain biogeocenosis showed that all of the horizons contain spirilla, which are typical hydrobionts, and pigmented coryneform bacteria associated with the herbaceous plants of the flood-plain meadows. The alluvial meadow soils of the inundated regions of the floodplain differed from the unflooded regions of the flood-plain in that they had a more diverse bacterial population continuously distributed over the soil profile.

[Bacterial soil variety: evaluation of methods, possibilities, and prospects ]

The paper presents a comparative description of the modern molecular genetic and routine culture techniques for assessing microbial diversity in soils and gives analysis for the different results obtained by these two groups of methods. The necessity of the collaboration of soil scientists, microbiologists, and molecular biologists in integrating different research methods for a proper assessment of soil microbial diversity is discussed. The paramount importance of soil as the source and reserve of biodiversity on the Earth is emphasized.

[Regulation of the biomass and activity of soil microorganisms by microfauna]

Microcosm experiments showed that the microbial biomass and the respiration activity in soil were regulated by nematodes. Depending on nematode number and plant residue composition, the trophic activity of nematodes can either stimulate or inhibit microbial growth and respiration as compared to soil containing no nematodes. The stimulating effect was observed when nitrogen-free (starch) or low-nitrogen (wheat straw, C:N = 87) organic substrates were applied. Inhibition occurred when a substrate rich in nitrogen (alfalfa meal, C:N = 28) was decomposed and the nematode population exceeded the naturally occurring level. A conceptual model was developed to describe trophic regulation by microfauna (nematodes) of the microbial productivity and respiration activity and decomposition of not readily decomposable organic matter in soil. The stimulating and inhibiting influence of microfauna on soil microorganisms was not a linear function of the rate of microbial consumption by nematodes. These effects are largely associated with the induced change in the physiological state of microorganisms rather than with the mobilization of biogenic elements from the decomposed microbial biomass.

[Microsampling of rhizosphere soil and laboratory artefacts]

A parallel analysis of the microsamples of surrounding soil and microsamples of rhizosphere soil did not reveal the so-called rhizospheric effect. The data obtained showed that dilution significantly influences the results of determination of the number of soil microorganisms. The actual number of microorganisms revealed in soil samples greatly differed from the theoretically predicted values. The enumeration of microorganisms in soil microsamples by direct count and, especially, by the plating method with the use of conversion coefficients based on the degree of sample dilution gave erroneous results.

[Structure and function of microbial communities in soil from the southern Taiga]

General regularities in the structure of the microbial communities of southern taiga soil ecosystems and taxonomic differences between the microbial communities of soils with different hydrothermal characteristics are discussed with reference to the main types of soils of the Central State Forest Biosphere Reserve.

[Effect of phosphorus on the colonization of barley rhizosphere by microorganisms]

The mineral phosphorus supply produced two outbreaks in the bacterial population of the barley rhizosphere and rhizoplane but inhibited the growth of fungal mycelium. The inhibition of mycelial growth might be due to the exudation of specific inhibitors by barley roots, since the most pronounced inhibition was observed at high doses of supplementary phosphorus.

[Reproductive resting forms of Arthrobacter globiformis]

Submerged cultures of Arthrobacter globiformis grown in media unbalanced with respect to carbon and nitrogen sources were found to contain cells exhibiting features typical of resting forms: long-term viability, specific ultrastructure, dormant metabolism, and thermoresistance. Such cells were produced not only in the collection strain VKM B-1112, but also in the A. globiformis strains isolated from 2- to 3-million-year-old permafrost sediments.

[Population dynamics of oligosporous actinomycetes in Chernozem soil]

Investigation of the dynamics of an oligosporous actinomycete population in chernozem soil in the course of succession induced by soil wetting allowed us to reveal the time intervals and conditions optimal for the isolation of particular oligosporous actinomycetes. Saccharopolysporas and microbisporas proved to be best isolated in the early and late stages of succession, whereas actinomycetes of the subgroup Actinomadura and saccharomonosporas could be best isolated in the early and intermediate stages of succession.

[Growth kinetics of microorganisms with various ecological strategies in a dialysis culture at low specific growth rates]

A dialysis culture was found to be most suitable for studying the metabolism of microorganisms at a low specific growth rate. The biomass of all microorganisms studied in the dialysis culture increased with time in a linear fashion; hence, the energy spent for growth decreased in proportion to a decrease in the specific growth rate. Microorganisms growing in oligotrophous environment (Arthrobacter globiformis and Lipomyces tetrasporus ) spent much less energy comparing to microorganisms from eutrophic habitats (Pseudomonas fluorescens and Debaryomyces formicarius ).

[Dynamics of populations of microbial antagonists in nonsterile soil]

The interaction between populations was studied with Arthrobacter crystallopoietes and Streptomyces olivocinereus, an actinomycete producing the antibiotic heliomycin active against Gram-positive microorganisms. The two organisms were either cultivated together in a growth medium or the two populations were introduced simultaneously into nonsterile soil at different levels of population density. The antagonism was found in both cases: A. crystallopoietes cells died off when a population of the potential antagonist was added. The density of a population producing the antibiotic had to be sufficiently high for the antagonism to be manifested. The antagonism influenced the dynamics of a population of the antibiotic-sensitive microorganism. The results have confirmed earlier data to the effect that antibiotic synthesis is possible in nonsterile soil.

[Bacterial population dynamics in a soil--plant system]

The dynamics of Rhizobium leguminosarum and Arthrobacter crystallopoietes populations introduced into soil at different levels of density was studied in a zone near barley roots. Microbial life with a high rate of growth was found only at the root surface. For A. crystallopoietes, the ultimate bacterial incidence at the root surface was found to depend on the original level of population density. For Rh. leguminosarum, the ultimate incidence was shown to reach an identical level irrespective of the original population density. Apparently, the identical level of stabilization in Rh. leguminosarum and the dependence of the ultimate incidence of A. crystallopoietes on the original population density reflect the peculiarities of ecological strategies displayed by these microorganisms. The introduction of A. crystallopoietes and Rh. leguminosarum into soil had no effect on the dynamics of soil bacteria assayed by the inoculation method.

[Relationship between the dynamics of the numbers of nodule bacteria in the soil and the stage of microbial succession]

The survival of a population of nodule bacteria after its introduction into soil depends on the ratio between favourable and unfavourable microzones. This ratio does not remain constant in one and the same soil at different stages of microbial succession even if the succession is caused by simple humidification of the soil without any introduction of additional substrates. The dynamics of the incidence of nodule bacteria introduced, at one and the same level, into soil samples of different growth stages of a complex of soil microorganisms significantly differed. Successful nitragination may be assisted by determining the growth stage of a microbial system when the population is being introduced and by changing the environment in the soil.

[Spatial factor in biodynamic studies of soils]

The role of the spatial factor in the dynamics of the soil bacteria incidence was studied. Multifactor dispersion analysis and a value for multiplicity of spatial straggling (Rp) must be used to detect changes in the incidence caused only by time. The value delta Rp has been introduced as an index for the maturity of the system soil-microorganisms.

[Criteria of microbial succession in soil]

The dynamics of bacterial and fungal incidence in two sharply different soil samples after the addition of water and glucose was studied using direct microscopic techniques and a technique of inoculation in growth media. The ratio of the population density indices established by means of microscopy to those found from the data of inoculation characterizes the stage of microbial succession. The techniques of microscopy and inoculation are equitable, furnish different information, and must be used in parallel while examining various problems pertinent to the dynamics of the soil microflora incidence.