Diversity ofArchaeain Bottom Sediments of the Discharge Areas With Oil- and Gas-Bearing Fluids in Lake Baikal

Diversity of NC10 Bacteria and ANME-2d Archaea in Sediments of Fault Zones at Lake Baikal

“…In the investigated sediments, we have indicated the presence of the archaeal mcrA genes of the ANME-2d subcluster using the additional PCR analysis and recently developed primers [41]. Since the general mcrA primer pair ME1F/ME2R [37] did not detect mcrA sequences of ANME-2d [60]; further still, the presence of these microorganisms and their diversity in environmental studies may be underestimated, as presently used primers simply do not capture them. Phylogenetic analysis has revealed that mcrA gene sequences from the areas of the methane seep PB and mud volcano M clustered together with available mcrA sequences of the known M. nitroreducens-like archaea from freshwater habitats and bioreactor, starting from paddy field soil, the Citarum River sediments and microbial mat [41].…”

“…Perhaps lack of nitrate and nitrite ions, being electron acceptors for AOM, in the sediments of Lake Baikal can be compensated, owing to the activity of archaea of the phylum Thaumarchaeota [79,80]. Ammonium-oxidizing members of this phylum at the investigated sites of Lake Baikal comprised a significant part of all analyzed archaea: up to 40% near the methane seep PB [59] and 20% near the mud volcano M [60].…”

“…Specific primers (Table 1) of mcrA gene did not detect members of the above mentioned ANME clusters in investigated DNA samples from deep sediments of Lake Baikal. Phylogenetic analysis indicated that all Baikal sequences of mcrA genes were similar to sequences of the order Methanomicrobiales and Methanosarcinales [60].…”

“…The structure of microbial communities was previously studied in deep sediments of methane seeps and mud volcanoes in Lake Baikal. However, no marine uncultivated anaerobic methanotrophic archaea of the ANME clusters were found either in surface sediments or zones of GH occurrence [57,59,60,68,73]. The absence of ANME clusters that are typical for marine ecosystems is understandable since in deep sediments of some gas-saturated areas (oil seeps and methane seeps), the concentration of sulfate ions is comparable with the reference values (up to 82 µM) [55,56], which is insufficient for the occurrence of geochemically significant sulfate-dependent AOM.…”

“…The process of AOM in deep sediments of Lake Baikal was detected by radioisotope techniques, with a maximum that was usually close to the GH layers, as well as by the shape of methane profile with depth typical for AOM [56,57]. Despite high methane concentrations in deep sediments of some sites of Lake Baikal (up to 15000 µM) that are sufficient to carry out of AOM [58], members of methane-oxidizing ANME clusters were not detected [57,59,60]. In this regard, it was suggested that the process could be carried out in methane-enriched freshwater lake sediments by other microorganisms, including ANME-2d archaea and NC10 bacteria.…”