ABSTRACTThe zonation of anaerobic methane-cyclingArchaeain hydrothermal sediment of Guaymas Basin was studied by general primer pairs (mcrI, ME1/ME2, mcrIRD) targeting the alpha subunit of methyl coenzyme M reductase gene (mcrA) and by new group-specificmcrAand 16S rRNA gene primer pairs. The mcrIRD primer pair outperformed the other generalmcrAprimer pairs in detection sensitivity and phylogenetic coverage. Methanotrophic ANME-1Archaeawere the only group detected with group-specific primers only. The detection of 14mcrAlineages surpasses the diversity previously found in this location. Most phylotypes have high sequence similarities to hydrogenotrophs, methylotrophs, and anaerobic methanotrophs previously detected at Guaymas Basin or at hydrothermal vents, cold seeps, and oil reservoirs worldwide. Additionally, fivemcrAphylotypes belonging to newly defined lineages are detected. Two of these belong to deeply branching new orders, while the others are new species or genera ofMethanopyraceaeandMethermicoccaceae. Downcore diversity decreases from all groups detected in the upper 6 cm (∼2 to 40°C, sulfate measurable to 4 cm) to only two groups below 6 cm (>40°C). Despite the presence of hyperthermophilic genera (Methanopyrus,Methanocaldococcus) in cooler surface strata, no genes were detected below 10 cm (≥60°C). WhilemcrA-based and 16S rRNA gene-based community compositions are generally congruent, the deeply branchingmcrAcannot be assigned to specific 16S rRNA gene lineages. Our study indicates that even among well-studied metabolic groups and in previously characterized model environments, major evolutionary branches are overlooked. Detecting these groups by improved molecular biological methods is a crucial first step toward understanding their roles in nature.
D:L-Amino Acid Modeling Reveals Fast Microbial Turnover of Days to Months in the Subsurface Hydrothermal Sediment of Guaymas Basin