The paper presents the results of studying quantitative dynamics, changes in the composition and species diversity (Shannon diversity index, SDI) of the cultured microbial community on samples of structural materials during the long-term exposure inside the International space station (space experiment Biorisk). It was found that the total number and species diversity of microorganisms changed in waves but the general trend was downward. In all, over the period of the experiment we detected, after cultivation in nutrient media, 20 bacterial species and 5 species of microscopic fungi grown on the samples of structural materials. Among bacteria, dominating species belonged to the Bacillus genus, and species of the normal cutaneous and mucous microbiota belonged to the Staphylococcus and Micrococcus genera. The Aspergillus and Penicillium genera dominated among fungi. Species diversity of the cultured microbial community was maximal for glass textolite and minimal for polyvinylchloride. SDI was 2.99 and 1.72, respectively. Also, these materials were populated by the largest (11) and least (5) numbers of cultured microorganisms. The low microbial load on all types of materials after different periods of exposure suggests eco-safety of the ISS environment and effectiveness of the respective control measures.

The paper presents the results of studying resistance of spores from «terrestrial» and «space» Bacillus licheniformis strains to antimicrobial agents, ultraviolet and radiation. It was established that the resistance of «space» strains to the influence of these extreme factors was noticeably more than for "terrestrial" strains. The most probable explanation of the stronger resistance of «space» strains can be genetic changes aimed to activate intracellular adaptive mechanisms preserved in succeeding generations. Spores from B. licheniformis 24 strain isolated from the ISS environment and exposed to the outer space as part of the EXPOSE-R2 experiment were found to have weakened resistance to antimicrobial agents in subsequent generations. Some of the «space» strains showed the ability to survive exposure to high doses of pulsed UV (1 kJ/m2) and ionizing radiation (20 kGy).

This study aimed to evaluate the suitability of two bioaerosol generation systems (dry and wet generation) for the aerosolization of microorganisms isolated from the International Space Station, and to calibrate the produced bioaerosols to fulfill the requirements of computational fluid dynamics model (CFD) validation. Concentration, stability, size distribution, agglomeration of generated bioaerosol and deposition of bioaerosols were analyzed. In addition, the dispersion of non-viable particles in the air was studied. Experiments proved that wet generation from microbial suspensions could be used for the production of well-calibrated and stabile bioaerosols for model validation. For the simulation of the natural release of fungal spores, a dry generation method should be used. This study showed that the used CFD model simulated the spread of non-viable particles fairly well. The mathematical deposition model by Lai and Nazaroff could be used to estimate the deposition velocities of bioaerosols on surfaces, although it somewhat underestimated the measured deposition velocities.

It was established that the biomass of fungal mycelium decreased by 30–50% during passage through the intestine of the Aporrectodea caliginosa and Lumbricus terrestris earthworms, while its content in empty intestines was 40–60% less than in the soil. It was found that the amount of mycelium increases again in three-day-old coprolites due to the rapid growth of the species. It was demonstrated that the physiological activity of fungi (estimated according to the time of the appearance of colonies on the medium and probability of propagation) is lower in the intestine content, digestive tract, and fresh excrement of the worms than in the soil. It was noted that the activity and diversity of organic substrates (utilized by fungi), as well as proteolytic activity is lower in fungal isolates from the intestine than from the soil. It was registered that the death of a part of the fungi occurs in the worm intestine, while the physiological state changes in the animals withstanding the effect of the digestive medium.

Poisson distribution was shown to be applicable to the dynamics of emergence of fungal colonies on plates inoculated with pure cultures or environmental samples, indicating the possibility for application of Hattori approach for assessment of the physiological state of fungi. The differences in physiological activity of different fungal species and genera, between spores and mycelia, or between the fungal populations from different environments, were revealed using the t r (delay time for colony emergence) and λ (potential capacity for growth) parameters.

The water-stability of soil and coprolite aggregates in soddy-podzolic soils and the participation of fungi in the formation of water-stable aggregates from earthworm ( Aporrectodea caliginosa ) coprolites were assessed. The water stability of the soil and coprolite aggregates in the soils increased in the following sequence: potato field—mown meadow—mixed forest. The fungal mycelium reserves increased in the same sequence. The water stability of the coprolite aggregates of Aporrectodea caliginosa inhabiting these soils is 2–2.5 times higher than that of the soil aggregates of the same size (3–5 mm). The inhibition of the growth of fungi by cycloheximide decreased the water stability of the coprolite aggregates, on the average, by 15–20%.

A comparative assessment of the contents of total nitrogen, ammonium, nitrates, and fungal and bacterial biomasses and of the activity of nitrogen transformation in fresh casts of Aporrectodea caliginosa and in a soddy-podzolic soil was performed. The total content of nitrogen in the casts was similar to or slightly higher than that in the soil; the content of inorganic forms of nitrogen in the casts was significantly higher than in the soil. The intensities of ammonification, nitrification, and denitrification and the pool of microbial biomass with a predominance of fungi during the 1.5-week-long incubation were also significantly higher in the casts. The activity of nitrogen fixation in the casts was lower than that in the soil. In the course of the incubation, the values of these parameters in the casts became closer to those in the soil. The inhibition of fungi in the casts with cycloheximide resulted in an increasing content of inorganic nitrogen and a higher activity of denitrification. In our opinion, this phenomenon is related to the fact that limitation of the fungal growth decreases the intensity of immobilization of nitrates and the fungal competition with denitrifying bacteria for available carbon. It was supposed that the activation of the fungal growth via application of plant substrates into the soil with a high population density of earthworms could suppress the emission of gaseous nitrogen compounds. The soil processing by earthworms had a positive effect on the soil properties.

The responses of soil microorganisms to the action of gut fluids of three earthworm species, Aporrectodea caliginosa, Lumbricus terrestris and Eisenia fetida were investigated. It was found that the midgut fluid taken form anterior part of the digestive tract could suppress formation of colonies of bacteria, inhibit the germination of spores and reduce the radial growth rate of some fungal colonies. Heating the midgut fluid at 98 °C for 10 min did not eliminate its suppressive activity. This suggests that a non-protein compound (s) is involved in this action of the midgut fluid. The suppressing effects were shown to be selective towards soil bacteria. However, the responses of microbial cells to the midgut fluid did not correspond to the taxonomic affiliation of the microorganisms tested. The mechanism of the suppressing effect might be a destruction of microbial cell membranes, as demonstrated for the gut of soil millipedes. The selective activity of the gut fluid of earthworms could be a significant factor for the animal's nutrition as well as for regulating the steady state of the intestinal microbial community, and modification of microbial communities in soil.

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.