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The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl2-equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. Here, we investigate the microbial community structure and activities across the seawater-brine interface using a combined biogeochemical, next-generation sequencing, and lipid biomarker approach. Within the interface, we detected fatty acids that were distinctly 13C-enriched when compared to other fatty acids. These likely originated from sulfide-oxidizing bacteria that fix carbon via the reverse tricarboxylic acid cycle. In the lower part of the interface, we also measured elevated rates of methane oxidation, probably mediated by aerobic methanotrophs under micro-oxic conditions. Sulfate reduction rates increased across the interface and were highest within the brine, providing first evidence that sulfate reducers (likely Desulfovermiculus and Desulfobacula) thrive in the Kryos Basin at a water activity of only ~0.4 Aw. Our results demonstrate that a highly specialized microbial community in the Kryos Basin has adapted to the poly-extreme conditions of a DHAB with nearly saturated MgCl2 brine, extending the known environmental range where microbial life can persist.

The microbial community response to petroleum seepage was investigated in a whole round sediment core (16 cm length) collected nearby natural hydrocarbon seepage structures in the Caspian Sea, using a newly developed Sediment-Oil-Flow-Through (SOFT) system. Distinct redox zones established and migrated vertically in the core during the 190 days-long simulated petroleum seepage. Methanogenic petroleum degradation was indicated by an increase in methane concentration from 8 μM in an untreated core compared to 2300 μM in the lower sulfate-free zone of the SOFT core at the end of the experiment, accompanied by a respective decrease in the δ13C signal of methane from -33.7 to -49.5‰. The involvement of methanogens in petroleum degradation was further confirmed by methane production in enrichment cultures from SOFT sediment after the addition of hexadecane, methylnapthalene, toluene, and ethylbenzene. Petroleum degradation coupled to sulfate reduction was indicated by the increase of integrated sulfate reduction rates from 2.8 SO42-m-2 day-1 in untreated cores to 5.7 mmol SO42-m-2 day-1 in the SOFT core at the end of the experiment, accompanied by a respective accumulation of sulfide from 30 to 447 μM. Volatile hydrocarbons (C2-C6 n-alkanes) passed through the methanogenic zone mostly unchanged and were depleted within the sulfate-reducing zone. The amount of heavier n-alkanes (C10-C38) decreased step-wise toward the top of the sediment core and a preferential degradation of shorter (n-alkanes (>C30) was seen during the seepage. This study illustrates, to the best of our knowledge, for the first time the development of methanogenic petroleum degradation and the succession of benthic microbial processes during petroleum passage in a whole round sediment core.

Anaerobic microbial hydrocarbon degradation is a major biogeochemical process at marine seeps. Here we studied the response of the microbial community to petroleum seepage simulated for 190 days in a sediment core from the Caspian Sea using a sediment-oil-flow-through (SOFT) system. Untreated (without simulated petroleum seepage) and SOFT sediment microbial communities shared 43% bacterial genus-level 16S rRNA-based operational taxonomic units (OTU0.945) but shared only 23% archaeal OTU0.945. The community differed significantly between sediment layers. The detection of fourfold higher deltaproteobacterial cell numbers in SOFT than in untreated sediment at depths characterized by highest sulfate reduction rates and strongest decrease of gaseous and mid-chain alkane concentrations indicated a specific response of hydrocarbon-degrading Deltaproteobacteria. Based on an increase in specific CARD-FISH cell numbers, we suggest the following groups of sulfate-reducing bacteria to be likely responsible for the observed decrease in aliphatic and aromatic hydrocarbon concentration in SOFT sediments: clade SCA1 for propane and butane degradation, clade LCA2 for mid- to long-chain alkane degradation, clade Cyhx for cycloalkanes, pentane and hexane degradation, and relatives of Desulfobacula for toluene degradation. Highest numbers of archaea of the genus Methanosarcina were found in the methanogenic zone of the SOFT core where we detected preferential degradation of long-chain hydrocarbons. Sequencing of masD, a marker gene for alkane degradation encoding (1-methylalkyl)succinate synthase, revealed a low diversity in SOFT sediment with two abundant species-level MasD OTU0.96.

Heterotrophic bacteria in the ocean initiate biopolymer degradation using extracellular enzymes that yield low molecular weight hydrolysis products in the environment, or by using a selfish uptake mechanism that retains the hydrolysate for the enzyme‐producing cell. The mechanism used affects the availability of hydrolysis products to other bacteria, and thus also potentially the composition and activity of the community. In marine systems, these two mechanisms of substrate processing have been studied in the water column, but to date, have not been investigated in sediments. In surface sediments from an Arctic fjord of Svalbard, we investigated mechanisms of biopolymer hydrolysis using four polysaccharides and mucin, a glycoprotein. Extracellular hydrolysis of all biopolymers was rapid. Moreover, rapid degradation of mucin suggests that it may be a key substrate for benthic microbes. Although selfish uptake is common in ocean waters, only a small fraction (0.5%–2%) of microbes adhering to sediments used this mechanism. Selfish uptake was carried out primarily by Planctomycetota and Verrucomicrobiota. The overall dominance of extracellular hydrolysis in sediments, however, suggests that the bulk of biopolymer processing is carried out by a benthic community relying on the sharing of enzymatic capabilities and scavenging of public goods. [ABSTRACT FROM AUTHOR]

The anaerobic formation and oxidation of methane involve unique enzymatic mechanisms and cofactors, all of which are believed to be specific for C[sub.1]-compounds. Here we show that an anaerobic thermophilic enrichment culture composed of dense consortia of archaea and bacteria apparently uses partly similar pathways to oxidize the C[sub.4] hydrocarbon butane. The archaea, proposed genus Candidatus Syntrophoarchaeum, show the characteristic autofluorescence of methanogens, and contain highly expressed genes encoding enzymes similar to methyl-coenzyme M reductase. We detect butyl-coenzyme M, indicating archaeal butane activation analogous to the first step in anaerobic methane oxidation. In addition, Ca. Syntrophoarchaeum expresses the genes encoding -oxidation enzymes, carbon monoxide dehydrogenase and reversible C[sub.1] methanogenesis enzymes. This allows for the complete oxidation of butane. Reducing equivalents are seemingly channelled to HotSeep-1, a thermophilic sulfate-reducing partner bacterium known from the anaerobic oxidation of methane. Genes encoding 16S rRNA and methyl-coenzyme M reductase similar to those identifying Ca. Syntrophoarchaeum were repeatedly retrieved from marine subsurface sediments, suggesting that the presented activation mechanism is naturally widespread in the anaerobic oxidation of short-chain hydrocarbons., Author(s): Rafael Laso-Prez [1, 2]; Gunter Wegener (corresponding author) [1, 2, 3]; Katrin Knittel [1]; Friedrich Widdel [1]; Katie J. Harding [1]; Viola Krukenberg [1, 2]; Dimitri V. Meier [1]; [...]

The short-chain hydrocarbons ethane, propane and butane are constituents of natural gas. They are usually assumed to be of thermochemical origin (1), but biological formation of ethane and propane has [...]

The spatial patterns of C[H.sub.4] and C[O.sub.2] assimilation are investigated in relation to the distribution of anaerobic methanotroph (ANME) groups and their associated bacteria from the anoxic Black Sea. The analysis has shown that since the methane formation requires the presence of methane and sulfate, the process is a rereaction of anaerobic oxidation of methane rather than net methanogenesis.

Author(s): Helge Niemann [1, 2, 5]; Tina Lösekann [1, 5]; Dirk de Beer [1]; Marcus Elvert [1, 6]; Thierry Nadalig [3, 6]; Katrin Knittel [1]; Rudolf Amann [1]; Eberhard J. [...]