Volume 92, Nº 2 (2023)

Abstract—Methoxylated aromatic compounds (MAC) are widely distributed in various habitats and are components of lignin, the second most abundant biopolymer on Earth. This review summarizes the results on microbiology, ecology, and biochemistry of anaerobic MAC catabolism in bacteria and archaea. We analyzed the genomes of 46 prokaryotes anaerobically degrading MAC for the presence of O-demethylase, CO-dehydrogenase/acetyl-CoA synthase, and benzoyl-CoA reductase genes, which determine the possibility of methoxydotrophic growth. It was found that facultative anaerobes of the phylum Pseudomonadota do not have any known genetic determinants of anaerobic O-demethylase reaction as well as of aromatic ring reduction. Thus, the MAC transformation by anaerobic microorganisms can be carried out by diverse biochemical mechanisms and probably plays a more significant role in the global carbon cycle than previously supposed.

Abstract—A new strain of methanogenic archaea, designated VT^T, was isolated from a sample of Spitsbergen permafrost. The cells were nonmotile curved rods, 2.7–5.3 × 0.3 µm. The optimal conditions for growth were 20°C, pH 6.6, and NaCl concentrations 0.03–0.05 M. The H₂/CO₂ gas mixture was the only substrate used. In the presence of H₂/CO₂, growth was stimulated by addition of yeast extract or rumen fluid. Phylogenetic analysis of the 16S rRNA gene sequences indicated that strain VT^T belonged to the genus Methanobacterium and was most closely related to M. lacus 17A1^T (97.02% similarity). Comparison of the sequenced and assembled genome of strain VT^T with the genomes of other members of this genus confirmed these results and revealed species-level differences. Our results indicate that this methanogenic isolate belongs to a new species of methanogenic archaea, for which the name Methanobacterium spitsbergensе sp. nov. was proposed, with the type strain VT^T (=VKM B-3566^T = JCM 39284^T).

Abstract—Three karst lakes were investigated in the Nizhny Novgorod region: Staropustynskie lakes Svyato and Nekrasov Bay and Lake Svetloyar. The studied lakes belonged to the mesotrophic-eutrophic polyhumous type and were characterized by stable stratification with signs of meromixia. Their water columns were divided into aerobic and anaerobic zones, with the bottom water containing sulfide. Fe(II) compounds were also present in the Staropustynskie lakes. In the Lake Nekrasov Bay, the mixolimnion showed a high rate of oxygenic photosynthesis, up to 1.2 µg С L^–1 day^–1, as well as a maximum of anoxygenic photosynthesis in the chemocline (0.030–0.706 µg С L^–1 day^–1) at a depth of 1.5–2.5 m. The peak of dark CO₂ assimilation (0.146 µg С L^–1 day^–1) occurred at a depth of 1.5 m in the oxycline zone. Anoxygenic phototrophic bacteria (APB) were found in the Lakes Zaliv Nekrasova and Svyato at the boundary of light penetration. Green sulfur bacteria with short cell prosthecate outgrowths, “Ancalochloris sp.,” predominated. Consortia “Chlorochromatium aggregatum” and filamentous chlorobacteria “Chloronema giganteum” were also found, their cell sheaths accumulated ferric iron salts. In the Staropustynskie lakes, various morphotypes of iron bacteria formed clusters in the microaerobic zone. In Lake Svetloyar the chemocline was located at a depth of 16 m, outside the photic zone, and the conditions were unfavorable for APB growth. In the studied lakes, heterotrophic aerobic bacteria played the main role in the aerobic oxidation of sulfur compounds in the chemocline zone.

Abstract—The optimal conditions for C3 oxidative biotransformation of 1.0 g/L pentacyclic triterpenoids oleanolic (OA) and glycyrrhetic (GA) acids were determined using the resting cells of Rhodococcus rhodochrous IEGM 1360 from the Regional Specialised Collection of Alkanotrophic Microorganisms. Suspensions of the resting cells with OD₆₀₀ 2.6 in pH 8.0 buffer and OD₆₀₀ 2.2 in pH 6.0 buffer showed the highest catalytic activity against OA and GA, which ensured the formation of 61 and 100% of their 3-oxo derivatives, respectively. Using phase contrast, atomic force, and confocal laser scanning microscopy, an adaptive response of rhodococci to the effects of OA and GA was revealed. In silico, the apoptotic and antioxidant activities of 3-oxo-OA and 3-oxo-GA, respectively, have been assumed. In vitro, a pronounced antibacterial activity of 3-oxo-OA against Micrococcus luteus, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was shown. The absence of toxic effects of the triterpenoids and their 3-oxo derivatives on aquatic and plant objects was demonstrated in silico and in vitro, respectively.

Abstract—Organization and localization of the alkB genes and of alkane 1-monooxygenases they encode in members of the genus Rhodococcus was investigated. All members of a phylogenetic group were found to possess specific types of the alkB genes (alkB1-type in the operons containing rubredoxin-coding genes, rubredoxin reductase, and a regulatory protein and/or alkB2-type in the operons lacking the rubredoxin-reductase-coding gene, and supplementary, separately located determinants of the alkB3−alkB8 type). The alkB1-type genes were present in the chromosomes of bacteria of groups B1 (R. aetherivorans, R. ruber), С (R. opacus, R. jostii, R. wratislaviensis, R. koreensis), D (R. erythropolis, R. qingshengii), G (R. triatomae), and E (R. fascians). The alkB2-type genes occurred in strictly specified loci of the chromosomes of members of the phylogenetic groups А (R. hoagii/R. equi), В2 (R. coprophilus, R. pyridinivorans, R. rhodochrous), and D (R. erythropolis, R. qingshengii). The separately located alkB3−alkB5 were revealed in the chromosomes of members of the D group D (alkB5 was found only in R. qingshengii), the alkB6 genes occurred in members of the groups B1 and В2, and alkB7−alkB8 were present in members of group Е. The proteins coded by the genes alkB1 and alkB2 belonged to three phylogenetic groups. The first one comprised AlkB1-type proteins of members of groups В1 and С and the AlkB2-type proteins of members of groups D and A. The second one was represented by AlkB2-type proteins of bacteria of group В2. The third group comprised AlkB1-type proteins of members of groups G and D. Alkane 1-monooxygenases encoded by separately localized genes alkB3−alkB8 were represented by three phylogenetic lineages: AlkB3−AlkB5, AlkB6, and AlkB7 and AlkB8. In the genome of R. pyridinivorans 5Ар, the genes alkB2 and alkB6 characteristic of group В1 were revealed. This determinants were shown to be required for biosurfactant synthesis. Emulsifying activity of the mutant with impaired alkB2 gene at 28 and 42°С was 16 and 3 times lower, respectively, while the amount of trehalose-containing surfactants decreased 7 and 3 times, respectively. Independent on the cultivation temperature, the mutant with impaired alkB6 gene exhibited 1.2 times lower emulsifying activity and more than twofold lower decrease of the synthesis of trehalose-containing surfactants. These results indicated the key role of alkB2 in biosurfactant synthesis at different cultivation temperatures. The role of alkB6 increased at 42°С, probably due to its elevated transcriptional activity.

Abstract—The diurnal dynamics of methane content in the near-bottom phototrophic biomass of the shallow soda Lake Bitter 1 (Gorchina 1) with a salinity of 30 g/L during the study period was investigated. The community was dominated by filamentous cyanobacteria, although no layered mat was formed. The maximum value of methane content up to 202.4 nmol CH₄/cm³ was revealed in the morning hours, which significantly exceeded the night values (28.9–42.8 nmol CH₄/cm³). Comparison of data on the content of methane with the relative abundance of cyanobacteria, methanogenic archaea, and methanotrophic bacteria during the twenty-four hours indicated that active processes of the methane cycle in soda lakes occurred not only in the sediments, but also in the near-bottom cyanobacterial communities. Methane content in the biomass of such a community is the result of a balance between the processes of its release by methanogens, consumption by methanotrophic bacteria, and natural degassing. It is assumed that the morning peak of methane content is associated with the release of hydrogen by diazotrophic cyanobacteria, which stimulates the development and activity of hydrogenotrophic methanogens of the genus Methanocalculus.