L. V. Lysak

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.

The role of microorganisms in the ecological functions of soils

The results of long-term investigations performed by researchers from the Department of Soil Biology at the Faculty of Soil Science of Moscow State University into one of the major functions of soil microorganisms—sustenance of the turnover of matter and energy in the biosphere—are discussed. Data on the population densities of soil microbes and on the microbial biomass in different types of soils are presented. The systemic approach has been applied to study the structural-functional organization of the soil microbial communities. The role of eukaryotic and prokaryotic microorganisms in the carbon and nitrogen cycles is elucidated. It is argued that the high population density and diversity of microorganisms are necessary to maintain the turnover of chemical elements in terrestrial ecosystems. The viability of microbes stored in the soils is important. New data on the preservation and survival of bacteria in nanoforms are presented. It is shown that peatlands and paleosols are natural banks, where microbes can be preserved in a viable state for tens of thousands years.

Study of ultramicrobacteria (Nanoforms) in soils and subsoil deposits by electron microscopy

The use of multiple centrifuging and filtration of water suspensions from different soils and subsoil deposits allowed revealing the ultrafine forms (nanosized, nanoforms) of bacteria. In the soils studied, the number of bacteria obtained by filtration using 0.2-μm filters was 20–300 mln cells in 1 g soil; the share of these bacteria of their total population in the natural soils reached 5% and was higher (up to 15%) in the polluted urban soils. The study of bacterial nanoforms in situ by the methods of scanning and transmission microscopy has shown the presence of dividing cells, which testifies to their viability. The cells without signs of division were similar in their ultrastructural characteristics to dormant forms of nonspore-forming bacteria. They were observed in permafrost deposits. The data obtained attest that the bacterial nanoforms are widespread in soils and subsoil deposits. According to their morphological and cytological characteristics, they are represented by both active and dormant forms to survive unfavorable conditions.

Quantity and taxonomic composition of ultramicrobacteria in soils

The number, physiological state, and taxonomic composition of ultramicrobacteria and archaea in various soils (alluvial meadow, sod-podzolic, leached chernozem, and peat) were studied. In all of the tested soil samples, a large number of ultramicrobacteria (tens and hundreds of millions of cells per 1 g of soil) was revealed by fluorescence microscopy. The portion of cells with intact membranes was larger among ultra-microbacteria than among the ordinary-size cells (95–98 and 50%, respectively). Ultramicrobacteria were characterized by high taxonomic diversity and included representatives of the main phylogenetic groups widespread in soils, such as Archaea, Actinobacteria, Cytophaga, and Proteobacteria. The results indicate that ultramicrobacteria are widespread in soils in a viable state and are involved in soil processes.

Analysis of Soil Bacterial Diversity: Methods, Potentiality, and Prospects

The paper presents a comparative description of the modern molecular genetic and routine culture techniques for assessing bacterial 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.

Bacterial complexes of the fruiting bodies and hyphosphere of certain basidiomycetes

The surface and internal tissues of the fruiting bodies of basidiomycetes were shown to be specific bacterial habitats characterized by varying diversity and structure of bacterial complexes. On the surface of fruiting bodies, gram-negative bacteria of the genera Pseudomonas, Xanthomonas, and Myxococcus prevailed, while in the internal tissues gram-positive bacteria of the genera Streptomyces, Bacillus, Arthrobacter, and Micrococcus were identified in addition. Bacterial complexes from the surface and inner tissues of the fruiting bodies of the studied basidiomycetes showed significant similarity to each other and differed from those from the hyphosphere and the reference soil. On the surface and in the internal tissues of the fruiting bodies, representatives of the genus Myxococcus were identified for the first time, which could indicate initial decay of the fruiting body.

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 it 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.

Assessment of the bacterial diversity in soils: Evolution of approaches and methods

This review analyzes the publications of Russian and foreign microbiologists presenting new approaches and methods for assessing the bacterial diversity of soils in the last twenty years. Using the example of peat soils, it is shown how the concepts of the diversity of the bacterial communities changed in conformity with the evolution of the analytical methods—from the traditional cultural to the molecular-biological ones. The data on the new phylotypes, genera, and species of bacteria adapted to growth in the acid medium and low temperatures characteristic of bog ecosystems are presented. Presently, one of the principal problems of soil microbiology is the necessity of the transfer from the databases on the microbial diversity constructed on the basis of molecular-biological methods to the analysis of the ecological functions of soil microorganisms. The prospects of the ecological evaluation of the bacterial diversity in soils based on the integration of different methods are discussed.

The effect of a bacterial-humus preparation on the biological activity of soils

The influence of the Gumigel bacterial-humus preparation on the biological activity of soils was investigated. The activity was assessed by the respiration intensity of the soil microorganisms, the total number of bacteria, and the structure of the saprotrophic bacterial complex. It was demonstrated that the microorganisms were preserved in the preparation for a long time. As this preparation was kept at 4°C, the number of microorganisms was preserved at a permanent level during no less than half a year. The preparation did not have a significant effect on the biological activity of the unpolluted soil, but it intensified the biological activity in the case of the polluted soil, which was seen from an increase in the number of microorganisms and their respiration intensity.