An inevitable decrease in oil production from reservoirs all over the world necessitates the application of microbial enhancement of oil recovery (MEOR) technologies. The high total salinity of formation water is a factor strongly suppressing the growth of most industry-applicable strains of hydrocarbon-oxidizing bacteria. The halotolerant strain Ectopseudomonas guguanensis G3 isolated from an oil reservoir (Republic of Kazakhstan) has demonstrated high efficiency of oil degradation and presumable biosurfactant production. The ability of the strain to utilize crude oil, n-alkanes, toluene, and xylene and its resistance to NaCl concentrations up to 6% were shown, as well as a high decrease in the interfacial tension of the culture liquid. Genomic analysis of the strain confirmed its ability to oxidize aromatic oil compounds and a wide range of n-alkanes (with a chain length up to C30) and revealed its potential capabilities to produce alginate, consume nitrate and urea as nitrogen sources, and synthesize betaine as an osmoprotectant. These findings demonstrate the high potential of E. guguanensis strain G3 to be used in oil reservoirs with high-salinity formation water in the biotechnology of oil displacement through oil degradation and in situ microbial metabolite production.

In 2024, an accident involving two tankers in the Kerch Strait resulted in the release of approximately 2400 tons of fuel oil into the Black Sea, causing significant contamination of seawater and the coastal zone. This study presents the first microbiological and molecular–ecological assessment of prokaryotic community composition and hydrocarbon-oxidizing bacteria (HOB) in coastal seawater and sand near Anapa (Russian Federation) following the spill. The taxonomic composition of nine samples was analyzed using high-throughput sequencing of 16S rRNA genes (V3–V4 regions), identifying Bacteria as the dominant domain (85.3–99.8%). In seawater samples, bacteria of the phyla Pseudomonadota, Cyanobacteriota, and Bacteroidota and archaea of the phyla Thermoplasmatota and Crenarchaeota predominated. Eighteen aerobic bacterial strains, including members of the genera Shewanella, Pseudoalteromonas, Halopseudomonas, Marinomonas, Pseudomonas, Vibrio, Alcanivorax, Ectopseudomonas, Nitratireductor, and Echinicola, were isolated from the zone of fuel oil spill. Several isolates demonstrated heavy oil degradation and biosurfactant production. Screening of collection strains isolated from other habitats revealed that Rhodococcus erythropolis TG65 and Marinobacter lutaoensis Pd1 and Pd2 degraded 92–94% of fuel oil n-alkanes. Elevated dissolved iron concentrations in the seawater indicate the possibility of a metabolic coupling between hydrocarbon oxidation and microbial iron reduction, mediated by indigenous Shewanella and Pseudomonas species. These findings indicate that indigenous HOB may contribute to the natural attenuation of aliphatic hydrocarbons in fuel oil.

The use of seawater with a high sulfate content for water-flooding of oil reservoirs contributes to the growth of sulfate-reducing bacteria (SRB), producing sulfide, which causes oil souring, corrosion of steel equipment, and environmental problems during oil production and refining. The purpose of this work was to determine the composition of microorganisms and the physicochemical parameters of the production and injection water of the Prirazlomnoye offshore high-temperature oil field in order to improve our understanding of the corrosion-active microorganisms. High-throughput sequencing of V3-V4 fragments of the 16S rRNA gene, quantitative PCR of bacteria and archaea, and cultural and analytical methods were used in the work. SRB, fermentative and syntrophic bacteria, and methanogenic archaea capable of participating in the processes of general and pitting corrosion of steel equipment were found in water samples. The production water contains sulfate, sulfide, and thermophilic SRB (Thermacetogenium and Desulfonauticus). Mixing of the produced water with seawater leads to its cooling and emergence of mesophilic SRB (Desulfobacter and Desulfogranum) in the water treatment system. Residual oil hydrocarbons and sulfides can be oxidized in the water treatment system, and the resulting metabolites serve as electron donors and acceptors for fermentative sulfidogenic bacteria (genera Caminicella, Kosmotoga, Petrotoga, and Geotoga). Sulfate-reducing and methanogenic enrichments from reservoir water produce sulfide and methane, respectively, receiving electrons from Fe0 in the absence of other sources of H2, which can contribute to pitting corrosion. This study allows for improving the ways to control sulfidogens and expands understanding of the microbial diversity of oil reservoirs.IMPORTANCEOil production from oil reservoirs with sulfate-containing formation water and injection seawater is accompanied by the appearance of sulfide in oil production, which increases the cost of oil refining and enhances corrosion processes of steel equipment. In this work, the physicochemical conditions and the composition of microorganisms in the produced and injected seawater at the Prirazlomnoye oil field (Russia) are investigated. The biocides used at the oil field are ineffective in suppressing sulfate-reducing bacteria (SRB), which are considered the main agents of microbial corrosion. It has been shown that not only SRBs but also fermenting bacteria inhabiting the oilfield were capable of producing sulfide. Enrichment cultures of autotrophic SRBs and methanogens capable of receiving electrons directly from Fe0 with the production of sulfide and methane, respectively, were obtained. The new scientific information obtained on microbial communities of oil reservoirs will make it possible to improve methods for monitoring corrosive microorganisms and selecting biocides.

Oil reservoirs with carbonate oil-bearing collectors are characterized by high fracturing. To improve the coverage of a reservoir by flooding, clogging agents should be introduced into the formation. In the patent literature, using sapropel as a plugging agent has been proposed. In the present work, application of cultural methods revealed that sapropel can be not only a dispersant, but also a source of aerobic hydrocarbon-oxidizing and anaerobic fermenting bacteria. Taxonomic analysis of the sapropel microbial community using high-throughput sequencing of the 16S rRNA gene V3–V4 region showed predominance of bacteria of the genus Streptomyces (40.7

Long-standing and chronic soil pollution in the Polar Regions is the most persistent. Simultaneous contamination with petroleum products and heavy metals puts additional load on the soil microbial community. The purpose of this work was to determine the composition of prokaryotes in the soils of Mount Kaskama with long-standing contamination with petroleum products and heavy metals (Murmansk region, Russia) and outside this zone and the potential ability of bacteria to participate in the self-purification of these soils. Using high-throughput sequencing of 16S rRNA gene V3-V4 fragments, an increase in the proportion of bacteria of the phyla Pseudomonadota, Verrucomicrobiota, Cyanobacteriota, and Bacillota was shown with an increase in soil contamination. Bacteria of the genera Bacillus, Caballeronia, Cytobacillus, Paenibacillus, Paraburkholderia, Pseudomonas, and Rhodanobacter were isolated from soil samples. Bacteria of the genus Paenibacillus capable of hydrocarbon oxidation and iron reduction were isolated from the subsurface contaminated layers. Under aerobic conditions, Fe(II) oxidation by bacteria of the genus Pseudomonas and biodegradation of hydrocarbons by isolated bacteria are possible. The isolated strains grew at low temperatures, used diesel fuel components, and were resistant to Cu(II), Ni(II), and Pb(II). The data obtained indicates the adaptation of bacterial communities to environmental conditions and the ability to participate in the process of soil self-healing.

Phytoremediation of oil pollution using free-floating aquatic plants is a promising method for water body cleaning. In this study, the influence of Eichhornia crassipes and Pistia stratiotes on the degradation of oil pollution was investigated. The loss of oil alkanes and the rheological characteristics of water were evaluated, and an analysis of the emerging rhizospheric microbial communities was carried out using high-throughput sequencing. The presence of E. crassipes and P. stratiotes plants in oil-contaminated tanks had no effect on the degradation of oil alkanes. However, the presence of plants promoted the development of rhizospheric bacteria capable of growing in oil-contaminated environments. Alpha diversity of microbial communities in oil-contaminated samples was higher in the presence of plants. Additionally, plants significantly reduced the water/oil interfacial tension, which facilitated the availability of hydrocarbons for biodegradation. A difference was noted in the microbiome between E. crassipes and P. stratiotes. Changes in the composition of microbial communities highlight the potential of E. crassipes and P. stratiotes as rhizospheric hosts for microorganisms in the phytoremediation of water bodies.

The development of microbial biofilms increases the survival of microorganisms in the extreme conditions of ecosystems contaminated with components of liquid radioactive waste (LRW) and may contribute to the successful bioremediation of groundwater. The purpose of this work was to compare the composition of the microorganisms and the exopolysaccharide matrix of the biofilms formed on sandy loams collected at the aquifer from a clean zone and from a zone with nitrate and radionuclide contamination. The aquifer is polluted from the nearby surface repository for liquid radioactive waste (Russia). The phylogenetic diversity of prokaryotes forming biofilms on the sandy loams’ surface was determined during 100 days using high-throughput sequencing of the V4 region of the 16S rRNA genes. Scanning electron microscopy was used to study the development of microbial biofilms on the sandy loams. The ratio of proteins and carbohydrates in the biofilms changed in the course of their development, and the diversity of monosaccharides decreased, depending on the contamination of the sites from which the rocks were selected. The presence of pollution affects biofilm formation and EPS composition along with the dominant taxa of microorganisms and their activity. Biofilms establish a concentration gradient of the pollutant and allow the microorganisms involved to effectively participate in the reduction of nitrate and sulfate; they decrease the risk of nitrite accumulation during denitrification and suppress the migration of radionuclides. These biofilms can serve as an important barrier in underground water sources, preventing the spread of pollution. Pure cultures of microorganisms capable of forming a polysaccharide matrix and reducing nitrate, chromate, uranyl, and pertechnetate ions were isolated from the biofilms, which confirmed the possibility of their participation in the bioremediation of the aquifer from nonradioactive waste components and the decrease in the radionuclides’ migration.

The search for the microorganisms responsible for sulfide formation and corrosion of steel equipment in the oil fields of Tatarstan (Russia) resulted in the isolation of a new halotolerant strictly anaerobic sulfate-reducing bacterium, strain 5S69T. The cells were motile curved Gram-negative rods. Optimal growth was observed in the presence of 2.0–4.0% (w/v) NaCl, at pH 6.5, and at 23–28 °C under sulfate-reducing conditions. The isolate was capable of chemoorganotrophic growth with sulfate and other sulfoxides as electron acceptors, resulting in sulfide formation; and of pyruvate fermentation resulting in formation of H2 and acetate. The strain utilized lactate, pyruvate, ethanol, methanol, fumarate, and fructose, as well as H2/CO2/acetate for sulfate reduction. The genome size of the type strain 5S69T was 4.16 Mb with a G + C content of 63.0 mol%. On the basis of unique physiological properties and results of the 16S rRNA gene-based phylogenetic analysis, phylogenomic analysis of the 120 conserved single copy proteins and genomic indexes (ANI, AAI, and dDDH), assigning the type strain 5S69T ((VKM B-3653T = KCTC 25499T) to a new species within the genus Pseudodesulfovibrio, is suggested, with the proposed name Pseudodesulfovibrio methanolicus sp. nov. Genome analysis of the new isolate showed several genes involved in sulfate reduction and its sulfide-producing potential in oil fields with high saline formation water.

Sulfidogenic bacteria cause numerous issues in the oil industry since they produce sulfide, corroding steel equipment, reducing oil quality, and worsening the environmental conditions in oil fields. The purpose of this work was to isolate and taxonomically identify the sulfidogenic bacteria responsible for the corrosion of steel equipment at the Karazhanbas oil field (Kazakhstan). In this study, we characterized five sulfidogenic strains of the genera Pseudodesulfovibrio, Oleidesulfovibrio, and Acetobacterium isolated from the formation water of the Karazhanbas oil field (Kazakhstan). Sulfate-reducing strain 9FUST revealed 98.9% similarity of the 16S rRNA gene sequence with the closely related strain ‘Pseudodesulfovibrio methanolicus’ 5S69T and was studied in detail to enhance the taxonomic resolution. Strain 9FUST grew optimally at 23–28 °C, pH 6.5, and 0–2% (w/v) NaCl. The strain used lactate, pyruvate, methanol, ethanol, fructose, ribose, and H2/CO2 (in the presence of acetate) as carbon and energy sources for sulfate reduction. Iso-C17:1 ω11, C15:0, iso-C15:0, and C16:0 were the predominant fatty acids. The genome is 4.20 Mbp with a G + C content of 64.0%. The average nucleotide identity and digital DNA–DNA hybridization values with Pseudodesulfovibrio spp. genomes were 72.5–91.6% (<95%) and 18.5–45.0% (<70%), respectively, and supported our conclusion that 9FUST (=VKM B-3654T = KCTC 25498T) belonged to a novel Pseudodesulfovibrio species, for which the name Pseudodesulfovibrio karagichevae sp. nov. is proposed. Pangenome analysis of sixteen Pseudodesulfovibrio species and functional annotation analysis of identified genes revealed complete modules of enzymes of the main metabolic pathways, characteristic of bacteria of this genus, and unique genes highlighting the adaptations of strain 9FUST in carbohydrate metabolism, nutrient uptake, and environmental stress response. Isolation of these strains expands our understanding of the diversity of sulfidogens in oil reservoirs and can be used to test the effectiveness of biocides used in an oil field.

Natural peatlands represent a wide range of habitats that contribute to the conservation of biodiversity, including microbial biodiversity. Molecular biological methods make it possible to significantly increase the accounting of microbial diversity compared to the cultivation methods. The studies on microbial diversity in minerotrophic peatlands using molecular biological methods lag significantly behind such studies for ombrotrophic peatlands. In this work, we characterized the taxonomic composition and functional potential of the prokaryotic community of the minerotrophic pine swamp (fen) in the Tver region of northwestern Russia using high-throughput sequencing of 16S rRNA gene fragments. This study is unique, since it was carried out not in individual horizons but across the entire fen profile, taking into account the differentiation of the profile into the acrotelm and catotelm. The composition and dominants of bacterial and archaeal communities were determined not only at the level of phyla but also at the level of classes, families, and cultivated genera. The prokaryotic community of the studied fen was shown to have a high taxonomic diversity (28 bacterial and 10 archaeal phyla were identified). The profile differentiation of the taxonomic composition of prokaryotic communities is most clearly manifested in the analysis of the acrotelm and catotelm. In the bacterial communities of the acrotelm, the top three phyla included Acidobacteriota, Alphaproteobacteria, and Actinomycetota, in the catotelm—Betaproteobacteria, Bacteroidota, and Chloroflexota. In archaeal communities of the acrotelm, we discovered the monodominance of Nitrososphaerota, in the catotelm—the dominance of Bathyarchaeota and subdominance of Thermoplasmatota, Halobacterota, and Aenigmarchaeota. The hot spots of microbial diversity in the studied fen profile were found to be the 0–20 cm layer of the acrotelm and the 150–200 cm layer of the catotelm. In contrast to the taxonomic composition, the functional profiles of the prokaryotic communities of the acrotelm and catotelm were generally similar, except for methane metabolism, which was primarily carried out in the catotelm.

The reserves of light conditional oil in reservoirs with low-salinity formation water are decreasing worldwide, necessitating the extraction of heavy oil from petroleum reservoirs with high-salinity formation water. As the first stage of defining the microbial-enhanced oil recovery (MEOR) strategies for depleted petroleum reservoirs, microbial community composition was studied for petroleum reservoirs with high-salinity formation water located in Tatarstan (Russia) using metagenomic and culture-based approaches. Bacteria of the phyla Desulfobacterota, Halanaerobiaeota, Sinergistota, Pseudomonadota, and Bacillota were revealed using 16S rRNA-based high-throughput sequencing in halophilic microbial communities. Sulfidogenic bacteria predominated in the studied oil fields. The 75 metagenome-assembled genomes (MAGs) of prokaryotes reconstructed from water samples were assigned to 16 bacterial phyla, including Desulfobacterota, Bacillota, Pseudomonadota, Thermotogota, Actinobacteriota, Spirochaetota, and Patescibacteria, and to archaea of the phylum Halobacteriota (genus Methanohalophilus). Results of metagenomic analyses were supported by the isolation of 20 pure cultures of the genera Desulfoplanes, Halanaerobium, Geotoga, Sphaerochaeta, Tangfeifania, and Bacillus. The isolated halophilic fermentative bacteria produced oil-displacing metabolites (lower fatty acids, alcohols, and gases) from sugar-containing and proteinaceous substrates, which testify their potential for MEOR. However, organic substrates stimulated the growth of sulfidogenic bacteria, in addition to fermenters. Methods for enhanced oil recovery should therefore be developed, combining the production of oil-displacing compounds with fermentative bacteria and the suppression of sulfidogenesis.

Intensive human activity in the Arctic region leads to hydrocarbon pollution of reservoirs and soils. Isolation of bacteria capable of growing at low temperatures and degrading oil and petroleum products is of scientific and practical value. The aim of this work was to study the physiology and growth in oil at temperatures below 0 °C of four strains of bacteria of the genera Pseudomonas, Rhodococcus, Arthrobacter, and Sphingomonas—previously isolated from diesel-contaminated soils of the Franz Josef Land archipelago—as well as genomic analysis of the Sphingomonas sp. AR_OL41 strain. The studied strains grew on hydrocarbons at temperatures from −1.5 °C to 35 °C in the presence of 0–8% NaCl (w/v). Growth at a negative temperature was accompanied by visual changes in the size of cells as well as a narrowing of the spectrum of utilized n-alkanes. The studied strains were psychrotolerant, degraded natural biopolymers (xylan, chitin) and n-alkanes of petroleum, and converted phosphates into a soluble form. The ability to degrade n-alkanes is rare in members of the genus Sphingomonas. To understand how the Sphingomonas sp. AR_OL41 strain has adapted to a cold, diesel-contaminated environment, its genome was sequenced and analyzed. The Illumina HiSeq 2500 platform was used for AR_OL41 genome strain sequencing. The genome analysis of the AR_OL41 strain showed the presence of genes encoding enzymes of n-alkane oxidation, pyruvate metabolism, desaturation of membrane lipids, and the formation of exopolysaccharides, confirming the adaptation of the strain to hydrocarbon pollution and low habitat temperature. Average nucleotide identity and digital DNA–DNA hybridization values for genomes of the AR_OL41 strain with that of the phylogenetically relative Sphingomonas alpine DSM 22537T strain were 81.9% and 20.9%, respectively, which allows the AR_OL41 strain to be assigned to a new species of the genus Sphingomonas. Phenomenological observations and genomic analysis indicate the possible participation of the studied strains in the self-purification of Arctic soils from hydrocarbons and their potential for biotechnological application in bioremediation of low-temperature environments.

The current work deals with genomic analysis, possible ecological functions, and biotechnological potential of two bacterial strains, HO-A22T and SHC 2-14, isolated from unique subsurface environments, the Cheremukhovskoe oil field (Tatarstan, Russia) and nitrate- and radionuclide-contaminated groundwater (Tomsk region, Russia), respectively. New isolates were characterized using polyphasic taxonomy approaches and genomic analysis. The genomes of the strains HO-A22T and SHC 2-14 contain the genes involved in nitrate reduction, hydrocarbon degradation, extracellular polysaccharide synthesis, and heavy metal detoxification, confirming the potential for their application in various environmental biotechnologies. Genomic data were confirmed by cultivation studies. Both strains were found to be neutrophilic, chemoorganotrophic, facultatively anaerobic bacteria, growing at 15–33 °C and 0–1.6% NaCl (w/v). The 16S rRNA gene sequences of the strains were similar to those of the type strains of the genus Ensifer (99.0–100.0%). Nevertheless, genomic characteristics of strain HO-A22T were below the thresholds for species delineation: the calculated average nucleotide identity (ANI) values were 83.7–92.4% (<95%), and digital DNA–DNA hybridization (dDDH) values were within the range of 25.4–45.9% (<70%), which supported our conclusion that HO-A22T (=VKM B-3646T = KCTC 92427T) represented a novel species of the genus Ensifer, with the proposed name Ensifer oleiphilus sp. nov. Strain SHC 2-14 was assigned to the species ‘Ensifer canadensis’, which has not been validly published. This study expanded the knowledge about the phenotypic diversity among members of the genus Ensifer and its potential for the biotechnologies of oil recovery and radionuclide pollution treatment.

A number of actinobacteria of the genus Gordonia are able to use dibenzothiophene (DBT) and its derivatives as the only source of sulfur, which makes them promising agents for the process of oil biodesulfurization. Actinobacteria assimilate sulfur from condensed thiophenes without breaking the carbon–carbon bonds, using the 4S pathway encoded by the dszABC operon-like structure. The genome of the new dibenzothiophene-degrading hydrocarbon-oxidizing bacterial strain Gordonia amicalis 6-1 was completely sequenced and the genes potentially involved in the pathways of DBT desulfurization, oxidation of alkanes and aromatic compounds, as well as in the osmoprotectant metabolism in strain 6-1 and other members of the genus Gordonia, were analyzed. The genome of G. amicalis strain 6-1 consists of a 5,105,798-bp circular chromosome (67.3% GC content) and an 86,621-bp circular plasmid, pCP86 (65.4% GC content). This paper presents a comparative bioinformatic analysis of complete genomes of strain 6-1 and dibenzothiophene-degrading Gordonia strains 1D and 135 that do not have the dsz operon. The assumption is made about the participation in this process of the region containing the sfnB gene. Genomic analysis supported the results of phenomenological studies of Gordonia strains and the possibility of their application in the bioremediation of oil-contaminated environments and in the purification of oil equipment from oil and asphalt-resin-paraffin deposits.

Microorganisms of the genus Bacillus were shown to have different effects on the degradation of polylactide packaging material. The degradation experiment was carried out on an agar medium at a temperature of 55°C and pH 5.9 for 14 days. This is the first report on the abiotic hydrolysis significantly slowing down during incubation with B. licheniformis S8 and occurring in parallel with the main process, enzymatic hydrolysis. The latter involved sequential cleavage of monomer units from the end of the macromolecule and the formation of low molecular weight products used by microorganisms as a substrate; it contributed to a decrease in the mass of polylactide by 5.1

Immobilized bacterial cells are presently widely used in the development of bacterial preparations for the bioremediation of contaminated environmental objects. Oil hydrocarbons are among the most abundant pollutants. We have previously described a new biocomposite material containing hydrocarbon-oxidizing bacteria (HOB) embedded in silanol-humate gels (SHG) based on humates and aminopropyltriethoxysilane (APTES); high viable cell titer was maintained in this material for at least 12 months. The goal of the work was to describe the ways of long-term HOB survival in SHG and the relevant morphotypes using the techniques of microbiology, instrumental analytical chemistry and biochemistry, and electron microscopy. Bacteria surviving in SHG were characterized by: (1) capacity for rapid reactivation (growth and hydrocarbon oxidation) in fresh medium; (2) ability to synthesize surface-active compounds, which was not observed in the cultures stored without SHG); (3) elevated stress resistance (ability to grow at high Cu2+ and NaCl concentrations); (4) physiological heterogeneity of the populations, which contained the stationary hypometabolic cells, cystlike anabiotic dormant forms (DF), and ultrasmall cells; (5) occurrence of piles in many cells, which were probably used to exchange genetic material; (6) modification of the phase variants spectrum in the population growing after long-term storage in SHG; and (7) oxidation of ethanol and acetate by HOB populations stored in SHG. The combination of the physiological and cytomorphological properties of the cells surviving in SHG for long periods may indicate a new type of long-term bacterial survival, i.e., in a hypometabolic state.

The development of Arctic regions leads to pollution of marine and coastal environments with oil and petroleum products. The purpose of this work was to determine the diversity of microbial communities in seawater, as well as in littoral and coastal soil, and the potential ability of their members to degrade hydrocarbons degradation and to isolate oil-degrading bacteria. Using high-throughput sequencing of the V4 region of the 16S rRNA gene, the dominance of bacteria in polar communities was shown, the proportion of archaea did not exceed 2% (of the total number of sequences in the libraries). Archaea inhabiting the seawater belonged to the genera Nitrosopumilus and Nitrosoarchaeum and to the Nitrososphaeraceae family. In the polluted samples, members of the Gammaproteobacteria, Alphaproteobacteria, and Actinomycetes classes predominated; bacteria of the classes Bacteroidia, Clostridia, Acidimicrobiia, Planctomycetia, and Deltaproteobacteria were less represented. Using the iVikodak program and KEGG database, the potential functional characteristics of the studied prokaryotic communities were predicted. Bacteria were potentially involved in nitrogen and sulfur cycles, in degradation of benzoate, terephthalate, fatty acids, and alkanes. A total of 19 strains of bacteria of the genera Pseudomonas, Aeromonas, Oceanisphaera, Shewanella, Paeniglutamicibacter, and Rhodococcus were isolated from the studied samples. Among them were psychrotolerant and psychrophilic bacteria growing in seawater and utilizing crude oil, diesel fuel, and motor oils. The data obtained suggest that the studied microbial communities could participate in the removal of hydrocarbons from arctic seawater and coastal soils and suggested the possibility of the application of the isolates for the bioaugmentation of oil-contaminated polar environments.

The work was aimed at investigation of the composition of microbial communities formed on the surface of samples of polyethylene terephthalate (PET), polystyrene (PS) and steel (ST) materials that were exposed in a small pond located at the territory of a solid waste landfill. The taxonomic composition of bacteria and fungi was determined by high-throughput sequencing of the V4 region of the 16S rRNA gene and of the ITS ribosomal operon, respectively. Bioinformatic analysis revealed predominance of bacteria of the phyla Pseudomonadota (Proteobacteria), Actinomycetota, Bacteroidota, and Bacillota in the biofilms formed on all samples. The observed quantitative changes in the composition of the dominant bacterial taxa were associated mainly with the exposure time, rather than the material of the samples. The iVikodak program was used to predict the functional characteristics of bacteria in the biofilms. The studied bacterial communities were shown to be potentially able to cause the degradation of polymer materials and xenobiotics and corrosion of steel. The fungal communities were dominated by saprotrophic representatives of the phyla Ascomycota and Basidiomycota. The effect of the conditions of the aquatic environment on the overall composition of the fungal community during exposure turned out to be less significant than that observed for bacteria; similar to the effect of the sample material, it could be traced for certain fungal genera. Among the dominant fungi, species potentially capable of biodegradation of polymers and corrosion of metals were identified. Microscopy confirmed the local degradation of the initial samples of materials as a result of exposure to the aquatic environment. Pure bacterial cultures of the genera Bacillus and Brevundimonas were isolated, which degraded alkanes, fatty acids, and phenols.

Actinomycetes are an important group of bioactive hydrolytic bacteria in any ecosystem. However, the actinomycete biodiversity in tropical ecosystems, particularly in Vietnam, is still underexplored. The aim of this article is to analyze the abundance, taxonomic structure and ecophysiological features of actinomycete complexes of soils and litter in Vietnam’s protected areas. A total of 41 samples of soils, plant litter and suspended soils were collected from six of Vietnam’s national parks and nature reserves. The direct inoculation technique showed that the total abundance of actinomycetes varied from 2.0 × 104 to 1.0 × 108 CFU/g. According to the luminescent microscopy with acridine orange dye, the length of the actinomycete mycelium was as long as 1000 m/g in the litter of Xuan Son National Park. A total of 80 strains were isolated and tested for antagonistic activity against Bacillus subtilis, Aspergillus niger and Candida albicans. Inoculation on Getchinson’s medium showed high cellulolytic activity. The most active strains were isolated from alluvial brown soil, plant litter and suspended soil of the Pu Hoat Nature Reserve. In these samples, actinomycetes adapted to high temperatures and low pH were found to be predominant. High-throughput sequencing of the V3–V4 region of the 16S rRNA gene and bioinformatic analysis confirmed the high taxonomic diversity and high hydrolytic activity of actinomycete complexes of the Pu Hoat Nature Reserve samples.

During the exploitation of oil reservoirs with highly mineralized waters, water separated from oil is pumped back into the reservoirs, which in some cases leads to an increase in ambient salinity and limits the possibility of application of biotechnologies for the enhancement of oil recovery. The microbial community of such oil fields has been relatively scarcely studied. Two strains of halophilic hydrocarbon-oxidizing bacteria, Halomonas titanicae TAT1 and Marinobacter lutaoensis KAZ22 were isolated from oil fields with mineralized formation water. Their physiological and genomic characteristics determining their presence in these habitats and the possibility of biotechnological application were investigated. The strains H. titanicae TAT1 and M. lutaoensis KAZ22 grew aerobically on crude oil in the temperature range from 4 to 42 and from 22 to 55°C, respectively, and had growth optima at salinity levels of 2–12 and 5–10% NaCl (wt/vol). Phenomenological observations of the degradation of oil n-alkanes were confirmed by the detection of three genes (alkB1, alkB2, and almA) encoding alkane1-monooxygenases in the genome of strain KAZ22 and of one alkB gene in the genome of strain TAT1. In the genome of the H. titanicae TAT1, all the genes for formation of osmoprotectants betaine, ectoine, and hydroxyectoine were annotated, and in the genome of M. lutaoensis KAZ22, the genes for the formation of ectoine and hydroxyectoine were annotated. The growth of strain KAZ22 on oil was accompanied by a decrease in the surface tension of the medium by more than 20 mN/m. Due to the absence of the nirK nitrite reductase gene, anaerobic growth of strain H. titanicae TAT1 in a medium with acetate and nitrate resulted in accumulation of ~100 mg/L of nitrite, which can inhibit the growth of sulfidogens. Considering the biological features of the strains and the results of genome analysis, injection of nitrate and strain H. titanicae TAT1 can be recommended for bioaugmentation of oil reservoirs with mineralized formation waters to suppress corrosion and decrease sulfide content, and injection of M. lutaoensis KAZ22, for remediation of oil pollution and increasing oil recovery from reservoirs.