Methanogenic capabilities of ANME ‐archaea deduced from 13 C ‐labelling approaches

Summary Anaerobic methanotrophic archaea ( ANME ) are ubiquitous in marine sediments where sulfate dependent anaerobic oxidation of methane ( AOM ) occurs. Despite considerable progress in the understanding of AOM , physiological details are still widely unresolved. We investigated two distinct microbial mat samples from the B lack S ea that were dominated by either ANME ‐1 or ANME ‐2. The 13 C lipid stable isotope probing ( SIP ) method using labelled substances, namely methane, bicarbonate, acetate, and methanol, was applied, and the substrate‐dependent methanogenic capabilities were tested. Our data provide strong evidence for a versatile physiology of both, ANME ‐1 and ANME ‐2. Considerable methane production rates ( MPRs ) from CO 2 ‐reduction were observed, particularly from ANME ‐2 dominated samples and in the presence of methane, which supports the hypothesis of a co‐occurrence of methanotrophy and methanogenesis in the AOM systems ( AOM / MPR up to 2:1). The experiments also revealed strong methylotrophic capabilities through 13 C ‐assimilation from labelled methanol, which was independent of the presence of methane. Additionally, high MPRs from methanol were detected in both of the mat samples. As demonstrated by the 13 C ‐uptake into lipids, ANME ‐1 was found to thrive also under methane free conditions. Finally, C 35 ‐isoprenoid hydrocarbons were identified as new lipid biomarkers for ANME ‐1, most likely functioning as a hydrogen sink during methanogenesis.