D. G. Zvyagintsev

Predation on fungal and bacterial biomass in a soddy-podzolic soil amended with starch, wheat straw and alfalfa meal

The variation in bacterial, fungal and total microbial biomass and activity was studied together with the abundance of soil nematodes and microarthropods after the addition of substrates differing in nitrogen availability to a soddy-podzolic soil. The experiments were carried out in microcosms with native and defaunated soil to evaluate stimulatory and suppressive effects of the microfauna on soil micro-organisms. Predation by microfauna (nematodes) and mesofauna (microarthropods) reduced the microbial biomass and microbial respiration by approximately 25% after addition of nitrogen rich alfalfa meal. When starch and wheat straw were supplied, the microbial biomass and activity were stimulated by up to 30% by grazing. Thus, the effect of predation on the microbiota depended on the composition of the available substrates and available nitrogen seems to be an important factor controlling stimulation or suppression of soil micro-organisms by the soil fauna when fresh organic compounds are accessible. The presence of soil fauna stimulated bacteria and, thus, reduced the fungal/bacterial ratio during the course of decomposition. In contrast, the fungal/bacterial ratio declined due to decreasing fungal biomass in defaunated soil.

Reproductive resting forms of Arthrobacter globiformis.

Submerged cultures ofArthrobacter 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-l 112, but also in the Aglobiformis strains isolated from 2-to 3-million-year-old permafrost sediments.

Culturable microorganisms from the earthworm digestive tract

The cultured aerobic copiotrophic bacteria and fungi from food-free digestive tracts of Aporrectodea caliginosa, Lumbricus terrestris, and Eisenia fetida earthworms, soil (compost), and fresh earthworm excrements were investigated. The microorganisms were isolated on nutrient media and identified by sequencing the fragments of bacterial 16S rRNA and fungal 28S rRNA (D1/D2 domain) gene sequences with subsequent phylogenetic analysis. Bacteria isolated from the digestive tracts of earthworms belonged to the families Aeromonadaceae, Comamonadaceae, Enterobacteriaceae, Flavobacteriaceae, Moraxellaceae, Pseudomonadaceae, and Sphingobacteriaceae (Bacteroidetes), as well as Actinobacteria. For five strains, namely Ochrobactrum sp. 341-2 (α-Proteobacteria), Massilia sp. 557-1 (β-Proteobacteria), Sphingobacterium sp. 611-2 (Bacteroidetes), Leifsonia sp. 555-1, and a bacterium from the family Microbacteriaceae, isolate 521-1 (Actinobacteria), the similarity to known 16S rRNA sequences was 93–97%; they therefore, probably belong to new species and genera. Bacterial groups isolated from the digestive tracts of earthworms were significantly different from those isolated from soil and excrements. Some bacterial taxa occurred in different sections of A. caliginosa intestine and in intestines of different earthworm species; however, the overall composition of bacterial communities in these objects is different. Existence of bacterial groupings symbiotically associated with intestines is proposed. Among the fungi, Bjerkandera adusta and Syspastospora parasitica were isolated from the cleaned digestive tracts as light-colored, sterile mycelium, as well as Geotrichum candidum, Acremonium murorum (A. murorum var. felina), Alternaria alternata, Aspergillus candidus, A. versicolor, Cladosporium cladosporioides, Rhizomucor racemosus, Mucor hiemalis, Fusarium (F. oxysporum, Fusarium sp.), and Penicillium spp. These fungi survive for a long time in the earthworm’s digestive environment. Investigation of the functional characteristics and role in the host organism is required to confirm the symbiotic status of the microorganisms associated with the earthworm digestive tract.

The Growth-promoting Effect of Beijerinckia mobilis 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 andClostridium 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, Clostridiumsp. 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. mobilisand Clostridiumsp. are discussed.

Population density and taxonomic composition of bacterial nanoforms in soils of Russia

The population density, physiological state, and taxonomic composition of bacterial nanoforms were first studied in soils of Russia. It was demonstrated with the help of fluorescent microscopy that the populations of nanoforms in the studied soils are very high and comprise tens and hundreds of millions of cells per 1 g of soil. The portion of cells with undamaged cell membranes was significantly higher in the nanoforms (95–98%) than in the cells of common size (about 50%), and this fact suggests the viability of the nanoforms. The taxonomic diversity of the nanoforms is great; the representatives of the main phylogenetic groups widespread in the soils were found among the nanoforms, namely, Archaea, Actinobacteria, Cytophaga, and Proteobacteria. The results allow assuming that the transformation of the cells into nanoforms is a relatively common event in the life of soil bacteria, allowing them to remain viable under unfavorable conditions and participate actively in soil processes.

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

A 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 (55–86%) in minerotrophic peatlands. 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.

Specificity of the Chitinolytic Microbial Complex of Soils Incubated at Different Temperatures

The structural and functional specificity of the chitinolytic microbial complex changes dramatically depending on the incubation temperature of soil microcosms. It was shown that the highest rates of chitin degradation occurred in desert soils at high temperatures (50°C); in the moderate and northern zones, these rates peaked at lower temperatures (5°C). The role of prokaryotes as the main chitin degraders in soils incubated at high temperatures, with fungi more actively participating in chitin decomposition at low temperatures, was shown for the first time. Fluorescent in situ hybridization (FISH) revealed the predominance of actinomycetes in the metabolically active chitinolytic prokaryotic complex of desert soils (high temperatures); in the soils of the northern latitudes (low temperatures), proteobacteria prevailed. The relationship between the taxonomic position of the dominant members of the chitinolytic complex of soil microorganisms, isolated in pure cultures with the dominant phylogenetic groups and the sequence types obtained by using molecular biological techniques (FISH) was revealed.

Some Approaches to the 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 the 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.

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.

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%.