Vol 93, No 4 (2024)

To study the mechanisms of protection of the cell membranes and macromolecules from cold, the composition of osmolytes, membrane lipids, and their fatty acids in a submerged culture of Mucor flavus was analyzed in growth dynamics at 20 and 4°C. This micromycete is psychrotolerant, having a wide growth temperature range (from –2 to 25°C) with an optimum at 20°C. Mucor flavus has a high growth rate (15 mm/day at 20°C, 4 mm/day at 0°C). At both temperatures, phosphatidic acids and phosphatidylethanolamines were predominant in the composition of membrane lipids, while phosphatidylcholines were the minor components. The main difference in the composition of membrane lipids was the threefold lower share of sterols at 4°C. During growth under optimal conditions, the proportion of phosphatidic acids decreased against the background of a slight increase in the levels of sterols, phosphatidylethanolamines, and phosphatidylcholines, while at 4°C the proportion of phosphatidic acids decreased slightly and the proportion of phosphatidylcholines increased. The fatty acids composition of phospholipids during growth at 20°C did not change significantly; linoleic, oleic, linolenic, and palmitic acids were predominant. At 4°C, the proportion of palmitic acid decreased and that of oleic acid increased, while the proportion of γ-linolenic acid decreased by half while that of α-linoleic acid increased. However, these changes did not lead to a significant change in the unsaturation degree of phospholipids, which varied between 1.5 and 1.6. Trehalose and glucose were the predominant osmolytes of the cytosol; glycerol was present in minor amounts only at 4°C. At both temperatures, the amount of osmolytes reached 3% of the dry weight in the course of growth, and the proportion of trehalose reached 70%. At both temperatures, a constant composition of osmolytes and slight changes in the composition of membrane lipids and their degree of unsaturation were observed, which probably contributes to the high growth rate of the fungus over a wide temperature range.

Complete genome sequencing of R. pyridinivorans strain 5Ар revealed the pSID plasmid (CP063453.1) 250428 bp in size. The gene responsible for replication of this plasmid is, most probably, dnaB. The genes which may be involved in the replication (dnaB, ssb) and plasmid separation after replication (parA) showed the highest similarity to the determinants located on large (224‒343 kb) plasmids of rhodococci: unnamed1 of R. pyridinivorans YF3, unnamed1 of R. rhodochrous LH-B3, pRJH1 of R. pyridinivorans YC-JH2, pRDE01 of Rhodococcus sp. RDE2, and pRho-VOC14-C342 of R. opacus VOC-14. The pSID plasmid was found to contain two loci responsible for the synthesis of secondary metabolites, one of them determining the synthesis of a polyketide compound (similar sequences have been revealed on plasmids of other rhodococci) and the other one probably determines the synthesis of a siderophore: the genes for biosynthesis of this compound (sid1–5) exhibited the highest similarity (not exceeding 75%) with the sequences from Streptomyces vilmorinianum YP1 (CP040244.1), S. ficellus NRRL 8067 (CP034279.1), Streptomyces sp. NBC00162 (CP102509.1), and some other streptomycetes, while showing no similarity to the known siderophore biosynthesis genes of rhodococci. The locus of the pSID plasmid responsible for the siderophore synthesis had a unique organization, since transcription of the sid5 (iucC) gene occurs in the opposite direction, while in other bacteria it belongs to an operon and is located at one of its termini. Inactivation of the sid1 gene was found to result in decreased antagonistic activity of R. pyridinivorans 5Ар against plant-pathogenic bacteria P. carotovorum 2.18, lower resistance to iron and cadmium ions and arsenate, as well as in emergence of phytotoxic properties against radish, while wild-type bacteria exhibit plant growth-promoting activity.

Rhodococcus rhodochrous strain М8 is a platform for development of the biotechnologies for biocatalytic production of acrylic monomers, the raw material for synthesis of acrylic heteropolymers. A genetic system for investigation of the cobalt-dependent transcription of nitrile hydratase genes in this strain was constructed, based the reporter gene of the metal-independent acylamidase from Rhodococcus qingshengii TA37. The cobalt-regulated promoter was shown to be located at a significant distance (~0.5 kb) from nitrile hydratase genes. Excision of the region between the promoter and the nitrile hydratase genes decreased significantly both the promoter activity and the degree of regulation by cobalt. Our results improve the possibilities for rational design of regulated expression cassettes using the promoter of nitrile hydratase genes in Rhodococcus, and for further development of biocatalysts based on these bacteria.

The complete genome sequence of a new strain of the haloarchaeaon Halorubrum distributum ICIS4 was revealed and analyzed. The strain was isolated from a culture of a carotenogenic microalga Dunaliella salina maintained in laboratory conditions for a long period of time. The genome (3.32 Mb) contained 3236 protein-coding genes. Of the 2817 groups of homologous genes, 11 were unique to this strain. In the genome, the genes were revealed, which were responsible for utilization of glycerol and starch and for synthesis of vitamins, pigments, and siderophores. These genes may be involved in formation and maintenance of the association with microalgae. A region similar to the HRPV9 virus and another circular contig similar to a phage of the haloarchaean Haloquadratum walsbyi were revealed in the genome assembly.

In all variants where carbon felt was present, imidacloprid degradation by the microflora of bottom sediments was many times higher than in the control, reaching 84.0 ± 1.7% under the polar connection of an external voltage source (1.2 V). When Shewanella oneidensis MR-1 was introduced, almost complete degradation of the pollutant was observed, while in the control without electrodes, it was 29.7 ± 6.0. The relative representation of the genes of the MtrB transmembrane protein of the respiratory chain, which is associated with exoelectrogenesis, depended on the external chain and had a maximum value when the voltage source was connected polarly, correlating with the pesticide degradation by the autochthonous microflora, similar to the DyP-type peroxidase genes. The introduction of S. oneidensis MR-1 resulted in an almost tenfold increase in the relative representation of DyP-type peroxidase genes. In all experimental variants, the values of the DyP relative representation were significantly higher than in the control without carbon felt, as well as the degree of imidacloprid degradation under these experimental conditions.

The Kaliningrad region has a rich historical heritage, including several water sources with high iron content. Known since the end of the 19th century, they are rich in ferrous iron, which is oxidized by bacterial communities. They include many different taxonomic groups of bacteria. In this work, for the first time, profiling of microbial communities of iron-containing sources in the Kaliningrad region was carried out; During the study, 6 samples were taken from four geographical locations. Based on the results of profiling, taxonomic groups were identified belonging to the phyla Acidobacteriota, Desulfobacteriota, Cyanobacteriota, Proteobacteria, Nitrospirota, and among the predominant groups the gammaproteobacterium of the genus Gallionella stands out.

Antifungal activity of newly synthesized submicrometer particles of the CsTeMoO₆ complex metal oxide was studied. They were found to inhibit spore germination of active micromycete degraders of industrial materials both in the dark and under illumination. Illumination increased the fungicidal activity of the studied compounds due to their photocatalytic activity. This is the first report on production of micromycete-resistant compositions of a number of polymers containing the complex metal oxides CsTeMoO₆ and RbTe_1.5W_0.5O₆. Upon addition of the studied complex oxides into the composition of the previously micromycete-sensitive materials, the latter were found to exhibit micromycete resistance both in the dark and under illumination. Treatment with light resulted in a more pronounced antifungal effect.