Thawing submarine permafrost is a source of methane to the subsurface biosphere. Methane oxidation in submarine permafrost sediments has been proposed, but the responsible microorganisms remain uncharacterized. We analyzed archaeal communities and identified distinct anaerobic methanotrophic assemblages of marine and terrestrial origin (ANME-2a/b, ANME-2d) both in frozen and completely thawed submarine permafrost sediments. Besides archaea potentially involved in anaerobic oxidation of methane (AOM) we found a large diversity of archaea mainly belonging toBathyarchaeota,Thaumarchaeota, andEuryarchaeota. Methane concentrations and δ¹³C-methane signatures distinguish horizons of potential AOM coupled either to sulfate reduction in a sulfate-methane transition zone (SMTZ) or to the reduction of other electron acceptors, such as iron, manganese or nitrate. Analysis of functional marker genes (mcrA) and fluorescencein situhybridization (FISH) corroborate potential activity of AOM communities in submarine permafrost sediments at low temperatures. Modeled potential AOM consumes 72–100% of submarine permafrost methane and up to 1.2 Tg of carbon per year for the total expected area of submarine permafrost. This is comparable with AOM habitats such as cold seeps. We thus propose that AOM is active where submarine permafrost thaws, which should be included in global methane budgets.

Strain NGK65^T, a novel hexadecane degrading, non-motile, Gram-positive, rod-to-coccus shaped, aerobic bacterium, was isolated from plastic polluted soil sampled at a landfill. Strain NGK65^T hydrolysed casein, gelatin, urea and was catalase-positive. It optimally grew at 28 °C, in 0–1% NaCl and at pH 7.5–8.0. Glycerol, d-glucose, arbutin, aesculin, salicin, potassium 5-ketogluconate, sucrose, acetate, pyruvate and hexadecane were used as sole carbon sources. The predominant membrane fatty acids were iso-C_16:0 followed by iso-C_17:0 and C_18:1 ω9c. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and hydroxyphosphatidylinositol. The cell-wall peptidoglycan type was A3γ, with ll-diaminopimelic acid and glycine as the diagnostic amino acids. MK 8 (H₄) was the predominant menaquinone. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NGK65^T belongs to the genus Nocardioides (phylum Actinobacteria ), appearing most closely related to Nocardioides daejeonensis MJ31^T (98.6%) and Nocardioides dubius KSL-104^T (98.3%). The genomic DNA G+C content of strain NGK65^T was 68.2%. Strain NGK65^T and the type strains of species involved in the analysis had average nucleotide identity values of 78.3–71.9% as well as digital DNA–DNA hybridization values between 22.5 and 19.7%, which clearly indicated that the isolate represents a novel species within the genus Nocardioides . Based on phenotypic and molecular characterization, strain NGK65^T can clearly be differentiated from its phylogenetic neighbours to establish a novel species, for which the name Nocardioides alcanivorans sp. nov. is proposed. The type strain is NGK65^T (=DSM 113112^T=NCCB 100846^T).

Microorganisms are known to be natural agents of biocorrosion and mineral transformation, thereby potentially affecting the safety of deep geological repositories used for high‐level nuclear waste storage. To better understand how resident microbial communities of the deep terrestrial biosphere may act on mineralogical and geochemical characteristics of insulating clays, we analyzed their structure and potential metabolic functions, as well as site‐specific mineralogy and element composition from the dedicated Mont Terri underground research laboratory, Switzerland. We found that the Opalinus Clay formation is mainly colonized by Alphaproteobacteria, Firmicutes, and Bacteroidota, which are known for corrosive biofilm formation. Potential iron‐reducing bacteria were predominant in comparison to methanogenic archaea and sulfate‐reducing bacteria. Despite microbial communities in Opalinus Clay being in majority homogenous, site‐specific mineralogy and geochemistry conditions have selected for subcommunities that display metabolic potential for mineral dissolution and transformation. Our findings indicate that the presence of a potentially low‐active mineral‐associated microbial community must be further studied to prevent effects on the repository's integrity over the long term.

Warming of the Arctic led to an increase in permafrost temperatures by about 0.3 ^∘C during the last decade. Permafrost warming is associated with increasing sediment water content, permeability, and diffusivity and could in the long term alter microbial community composition and abundance even before permafrost thaws. We studied the long-term effect (up to 2500 years) of submarine permafrost warming on microbial communities along an onshore–offshore transect on the Siberian Arctic Shelf displaying a natural temperature gradient of more than 10 ^∘C. We analysed the in situ development of bacterial abundance and community composition through total cell counts (TCCs), quantitative PCR of bacterial gene abundance, and amplicon sequencing and correlated the microbial community data with temperature, pore water chemistry, and sediment physicochemical parameters. On timescales of centuries, permafrost warming coincided with an overall decreasing microbial abundance, whereas millennia after warming microbial abundance was similar to cold onshore permafrost. In addition, the dissolved organic carbon content of all cores was lowest in submarine permafrost after millennial-scale warming. Based on correlation analysis, TCC, unlike bacterial gene abundance, showed a significant rank-based negative correlation with increasing temperature, while bacterial gene copy numbers showed a strong negative correlation with salinity. Bacterial community composition correlated only weakly with temperature but strongly with the pore water stable isotopes δ¹⁸O and δD, as well as with depth. The bacterial community showed substantial spatial variation and an overall dominance of Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadetes, and Proteobacteria, which are amongst the microbial taxa that were also found to be active in other frozen permafrost environments. We suggest that, millennia after permafrost warming by over 10 ^∘C, microbial community composition and abundance show some indications for proliferation but mainly reflect the sedimentation history and paleoenvironment and not a direct effect through warming.

Strain NGK35^T is a motile, Gram-stain-negative, rod-shaped (1.0–2.1 µm long and 0.6–0.8 µm wide), aerobic bacterium that was isolated from plastic-polluted landfill soil. The strain grew at temperatures between 6 and 37 °C (optimum, 28 °C), in 0–10 % NaCl (optimum, 1 %) and at pH 6.0–9.5 (optimum, pH 7.5–8.5). It was positive for cytochrome c oxidase, catalase as well as H₂S production, and hydrolysed casein and urea. It used a variety of different carbon sources including citrate, lactate and pyruvate. The predominant membrane fatty acids were C_16 : 1 cis9 and C_16 : 0, followed by C_17 : 0 cyclo and C_18 : 1 cis11. The major polar lipids were phosphatidylglycerol and phosphatidylethanolamine, followed by diphosphatidyglycerol. The only quinone was ubiquinone Q-8. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NGK35^T belongs to the genus Paenalcaligenes (family Alcaligenaceae ), appearing most closely related to Paenalcaligenes hominis CCUG 53761A^T (96.90 %) and Paenalcaligenes suwonensis ABC02-12^T (96.94 %). The genomic DNA G+C content of strain NGK35^T was 52.1 mol %. Genome-based calculations (genome-to-genome distance, average nucleotide identity and DNA G+C content) clearly indicated that the isolate represents a novel species within the genus Paenalcaligenes . Based on phenotypic and molecular characterization, strain NGK35^T can clearly be differentiated from its phylogenetic neighbours establishing a novel species, for which the name Paenalcaligenes niemegkensis sp. nov. is proposed. The type strain is NGK35^T (=DSM 113270^T=NCCB 100854^T).