Vol 88, No 3 (2019)

Microorganisms produce various volatile compounds, including volatile organic compounds and complex combinations of volatile compounds. The ecological and functional role of these compounds is presently the subject of intense study. Volatile organic compounds of microbial origin may possess antimicrobial properties, suppress or stimulate plant growth, and act as signals for long-distance communication between organisms (infochemicals), which propagate in the air and in aquatic solutions. Chemical diversity of volatile organic compounds of microbial origin provides a source of new compounds which may find application in medicine, biotechnology, and agriculture. Presently known bacterial volatile compounds, their structure, biosynthesis, and biological activity are discussed, with special emphasis on organic volatile compounds and their effect on bacteria.

Adaptive reactions of Arctic and Antarctic strains of psychrophilic micromycetes Geomyces pannorum and Thelebolus microsporus to growth within a broad temperature range were studied. Adaptation of these species to different temperatures was found to result from both morphological and biochemical changes, including changes in the concentration of small molecules and lipid membrane components. These biochemical, morphological, and physiological mechanisms exhibited the patterns common to all strains, as well as species and strain differences. The general patterns included temperature-dependent changes in amounts of monosaccharides, some disaccharides, and free linoleic and linolenic acids. The differences between the Arctic and Antarctic strains were mainly associated with the differences in lipid composition, while interspecies differences resulted from metabolomic modifications. Antarctic strains showed lower ability to survive elevated temperatures, which correlated with weaker manifestation of the lipid-dependent adaptive mechanisms compared to the Arctic strains. Among the interstrain differences, higher growth parameters and mannitol accumulation were found in the Arctic isolates. Adaptation of T. microsporus was characterized by more diverse changes in the concentrations of small organic molecules in the metabolome profile and by pronounced changes in mycelial morphology. The results of metabolomic analysis and their subsequent treatment by the methods of multivariant statistics supported the suggestion of higher dispersion of metabolomic characteristics under unfavorable conditions and of lower dispersion of metabolomic data under optimal conditions.

Biodegradation of liquid petroleum motor fuels and fuel mixtures containing biodiesel fuel (methyl ethers of rapeseed fatty acids) by aerobic acidophilic actinobacteria Mycobacterium sp. AG_S10 was studied. Strain AG_S10 was found to be able to grow on aviation kerosene Jet A-1 as the sole carbon and energy source under highly acidic conditions. After 21 days of cultivation at 30°C and pH 2.5, bacterial numbers increased from 4.2 × 10⁶ to 7.0 × 10⁸ cells/mL, while the hexane-soluble part of the fuel was degraded by 90.4%. The strain also utilized components of the winter diesel fuel, including С₈–С₂₀n-alkanes, iso-alkanes, and aromatic compounds. Overall hydrocarbon consumption under the same conditions was 99.4%. The ratio of (iso-С₁₉ (pristane) + iso-С₂₀ (phytane))/(n-С₁₇ + n-С₁₈) changed from 1.21 in the control to 2.39 in the experiment with bacterial degradation, which indicated preferable utilization of n-alkanes, rather than isoprenoids. Over 90% of diesel fuel hydrocarbons were consumed from day 4 to day 12 of cultivation, while abundance of the bacterial population increased by three orders of magnitude. Strain AG_S10 consumed both hydrocarbons and oxygen-containing (plant-derived) components of the fuel mixtures with biodiesel fuel. Bacteria preferentially consumed hydrocarbons, and the ratio between oil diesel fuel and biodiesel fuel in the mixture changed in the course of incubation.

Methanogenesis is the main source of biogenic methane in the atmosphere and therefore plays an important role in climate change. While all methanogens known until recently belonged to the phylum Euryarchaeota, potential methanogens were recently found among two uncultured archaeal phyla, Bathyarchaeota and Verstraetearchaeota. Analysis of the genomes of several members of Verstraetearchaeota revealed their ability to use methylated compounds for methanogenesis; however, all these genomes were incomplete, which prevents an unequivocal reconstruction of their metabolic pathways. The present work reports the complete genome of a new member of Verstraetearchaeota from the metagenome of the microbial community of a deep subsurface reservoir of thermal waters in Western Siberia. Phylogenetic analysis revealed the new archaeon to belong to a new species of the genus ‘Candidatus Methanosuratus’, for which the name ‘Candidatus Methanosuratus subterraneum’ was proposed. The possibility of methyl-reducing methanogenesis was indicated by the presence of the methyl coenzyme M reductase complex and of the genes required for methane production using methanol as the methyl group donor, while the genes required for the oxidation of methyl group to CO₂ were missing. Genome analysis showed that ‘Ca. Methanosuratus subterraneum’ has the metabolic pathways required for growth by fermentation of proteinaceous substrates. Analysis of the global distribution of ‘Ca. Methanosuratus’ revealed the 16S rRNA gene sequences assigned to this genus in hot springs, underground waters, and oil reservoirs, which makes it possible to consider this genus as a representative of the subsurface biosphere.

The research was aimed at detection of thermophilic microorganisms in Lake Baikal low-temperature sediments associated with discharge of gas-saturated fluids. Members of the order Clostridiales were revealed in enrichment cultures obtained from the bottom sediments at three sites (methane seep, oil-methane seep, and mud volcano). No thermophilic prokaryotes were found in the enrichment culture with sediment samples from a background area. The presence of thermophilic microorganisms at the sites of hydrocarbon discharge may result from their migration to the bottom surface with the gas-bearing mineralized fluid moving along the fracture zones. Unlike marine cold sediments, where the endospores of thermophilic bacteria belong to strict anaerobes existing due to fermentation of organic substrates or sulfate reduction, Lake Baikal sediments associated with discharge of gas-saturated fluids were found to contain facultatively anaerobic thermophilic prokaryotes.

The study aimed to investigate yeast communities in sugarcane (Saccharum officinarum Linn.) phylloplane in Thailand by a culture-dependent approach using a direct isolation method; namely, plating of leaf washing for yeast isolation. A total of 150 yeast strains were obtained from 79 sugarcane leaf samples collected in ten provinces. Identification on the basis of the D1/D2 region of the large subunit (LSU) rRNA gene sequence analysis revealed that 126 yeast strains (84%) were identified to be yeast in the phylum Basidiomycota and 24 strains (16%) were in the phylum Ascomycota. Basidiomycetous yeast consisted of 27 known species in 18 genera viz. Cystobasidium, Dioszegia, Dirkmeia, Hannaella, Jaminaea, Kwoniella, Langdonia, Moesziomyces, Occultifur, Papiliotrema, Piskurozyma, Pseudozyma, Rhodosporidiobolus, Rhodotorula, Saitozyma, Sporobolomyces, Symmetrospora and Tremella, whereas, ascomycetous yeast consisted of three species viz. Candida parapsilosis, Kodamaea ohmeri and Meyerozyma caribbica. In addition, the most common known yeast species detected were Dirkmeia churashimaensis with relative frequency and frequency of occurrence of 12.0 and 22.8%, respectively. Subsequently, seven strains were found to be five new yeast species, which were already proposed as Kalmanozyma vetiver, Wickerhamiella siamensis, Papiliotrema siamense, Hannaella phyllophila and Occultifur tropicalis. The results of this study revealed a higher number of yeast strains and species in the phylum Basidiomycota, which agreed with other reports. However, the present results are opposite to those of our previous study when the enrichment technique was used for yeast isolation.