Microbiology

Abstract. Active study of electrocatalytic properties of prokaryotes in the last 30 years has led to the creation of a new field of biotechnology – electricity generation in microbial fuel or electrolytic cells, where microbial cells act as biocatalysts of anodic or cathodic processes consuming organic matter or forming biomass and substances with added value during electrotrophic fixation of CO₂. The most economically promising is the use of microbial fuel cells (MFC) for wastewater treatment and in bioremediation processes. Recently, the prospects for the introduction of MFC or stimulation of electroactive microbial communities for the purification of oil-contaminated anaerobic layers of soils and marine sediments have been considered. However, this version of the technology has a number of significant technical limitations. We describe a laboratory sedimentary MFC with a bioanode and biocathode inoculated with oil-contaminated soil, which for 210 days of continuous operation was the only source of power supply for an autonomous sensor for monitoring ambient air parameters. Electric current generation in the MFC was accompanied by the destruction of hydrocarbons in contaminated soil and the formation of various microbial populations in the anaerobic soil layer, at the anode and at the cathode, in which potential oil destructors, electrogens and electrotrophs dominated, respectively. At the same time, the release of CO₂ against the background of ambient air was minimal, which indicates the formation of an effective gas filter in the MFC. Short-term incubation of the MFC in field conditions revealed a significant effect of temperature fluctuations on the physicochemical parameters of the device, its performance and the composition of the cathode microbial population. We consider in detail the changes in the phylogenetic and physiological diversity of microbial populations of different zones of the sedimentary MFC during its operation, and also outline the prospects and problems of the practical application of such systems for bioremediation of oil-contaminated soil.

Abstract. The paper presents the results of a study of the effect of ultra-weak magnetic fields (MF) on the viability, growth characteristics, respiratory activity, and antagonistic properties of microscopic fungi. The experiments were conducted on strains isolated from the interior of the International Space Station. To create hypomagnetic conditions (HMC), the hypomagnetic chambers GMK-1 and GMK-2, shielding the Earth’s MF, were used in the experiments. The chamber walls are a two-section magnetic screen made of amorphous permalloy tape. In the experiments, the GMK chambers made it possible to reduce the geomagnetic field by 1000–2000 times. The maximum value of the MF after demagnetization did not exceed 45 nT. It was found that the hypomagnetic field (HMC) did not have a predominantly inhibitory and/or stimulating effect on the viability of spores and the growth of fungal colonies, as indicated by the absence of reliable changes in the quantitative level, percentage of spore germination and radial growth rate of the tested strains in the HMC compared to geomagnetic conditions. At the same time, the growth and respiration rate of micromycetes in some cases was significantly stimulated in the GMF during their development on the surface of samples of structural materials under conditions of limited availability of nutrients. It was also found that the GMF affects the antagonistic properties of some microscopic fungi. The Penicillium rugulosum 633.12 strain grown in the GMF completely lost its antagonistic activity towards bacteria, which was found to be high when cultivated under standard geomagnetic conditions. The results obtained are discussed in the context of the features of microbial colonization of the habitat of future lunar complexes.

Abstract. The objective of this study is to characterize the relationship between the persistent profile and the ability to produce iron-binding compounds of intestinal isolates of E. coli and K. pneumoniae with the genetic determinants iucBC and clbBN, both at the phenotypic and genetic levels. The use of designed primers and a developed unified multiplex-PCR algorithm permitted the establishment of a wide frequency of occurrence (44.0–80.0%) among opportunistic strains of E. coli and K. pneumoniae cultures with genetic determinants clbBN and iucBC, which encode the synthesis of aerobactin and colibactin. The presence of the clbBN/iucBC genes in the genetic apparatus of enterobacteria was found to result in a pronounced ability to produce iron-binding compounds and a wide range of persistent characteristics (antilysozyme, anticarnosine, antipeptide activity with respect to TNFα, antiimmunoglobulin activity with respect to IgM/IgG and biofilm formation). A comparison of the genomes of sequenced clbBN⁺iucBC⁺ strains with those of clbBN^-iucBC^- strains revealed the presence of genes essential for the biosynthesis and transport of aerobactin, a comprehensive list of pks island genes, and the existence of known homologues of the lysozyme inhibitor determinants Ivy and MliC, EspP (E. coli M-17) and PliC, LprI (K. pneumoniae ICIS-278_PBV and K. pneumoniae ICIS-277_SVA) were identified. Therefore, strains of E. coli and K. pneumoniae that possess the genetic determinants of iron chelators, namely clbBN and iucBC, exhibit both genotypic and phenotypic indications of siderophore production and protease activity against host antimicrobial factors. This allows for the use of these strains as markers of the pathogenic and persistent potential of opportunistic enterobacteria.

Abstarct. Invasion by pathogens is accompanied by competitive interactions between the pathogens and the microbiota, by the allocation of a niche in the intestine for the pathogen, and induction of immune processes in the host organism. These processes are accompanied by the accumulation of microbiota secondary metabolites, which may result in alterations of physicochemical characteristics of the host gut. These events may affect the speed of progression of bacterial infections, including secondary bacterial infections. In this study, experimental evidence showed that within the initial 24-h period, both in vitro and in vivo, interaction between Bacillus thuringiensis (Bt) and the symbiotic bacterium Serratia liquefaciens caused alkalization of the medium: both the culture fluid and the midgut contents of the Colorado potato beetle (CPB). Combined oral administration of S. liquefaciens and Bt resulted in 83% mortality of CPB larvae as early as 48 h after the inoculation. This mortality rate was 8.3-fold higher than that (<10%) observed in individuals infected with Bt alone. Provision of food treated with Bt and a peptide fraction of S. liquefaciens metabolites to CPB larvae had analogous synergistic effects on mortality. It is possible that during an invasion by pathogens under conditions of the gut microbiota, there is an increase in the production of metabolites that can result in a release of inhibitors into the local medium. These inhibitors may then act as activators of Bt endotoxins (Cry toxins). This hypothesis requires further research.

Abstract. In this work, the resistance of Achromobacter insolitus LCu2 cells to copper (II) was reduced by adding 1 μM silver nanoclusters to the culture medium: the maximum tolerable concentration decreased by 4 times, the minimum inhibitory concentration – by 25 times. It is assumed that nanoclusters disrupt the functioning of the copper (II) efflux system through binding to the CusC protein, which leads to a partial loss of the ability of bacteria to export excess copper (II) cations from cells.

It is known that Glycine max and G. soja, entering into symbiotic relations with different rhizobia species, form nodules of determinate type. In such nodules, bacteroids are low differentiated and only slightly differ from free-living bacteria. Recently, it has been shown that in G. soja nodules when inoculated with Bradyrhizobium liaoningense strain RCAM04656, bacteroids were significantly larger than free-living bacteria. In this study, decreased temperature (21°C) was found to increase variation in the length of bacteroids in both G. max and G. soja nodules, with individual bacteroids increasing in size more than 15-fold over bacteria. At the optimal temperature (28°/24°C), the size of bacteroids varied to a lesser extent.