Physiological versatility of ANME-1 and Bathyarchaeotoa-8 archaea evidenced by inverse stable isotope labeling.

Background: The trophic strategy is one key principle to categorize microbial lifestyles, by broadly classifying microorganisms based on the combination of their preferred carbon sources, electron sources, and electron sinks. Recently, a novel trophic strategy, i.e., chemoorganoautotrophy-the utilization of organic carbon as energy source but inorganic carbon as sole carbon source-has been specifically proposed for anaerobic methane oxidizing archaea (ANME-1) and Bathyarchaeota subgroup 8 (Bathy-8).

Results: To further explore chemoorganoautotrophy, we employed stable isotope probing (SIP) of nucleic acids (rRNA or DNA) using unlabeled organic carbon and C-labeled dissolved inorganic carbon (DIC), i.e., inverse stable isotope labeling, in combination with metagenomics. We found that ANME-1 archaea actively incorporated C-DIC into RNA in the presence of methane and lepidocrocite when sulfate was absent, but assimilated organic carbon when cellulose was added to incubations without methane additions. Bathy-8 archaea assimilated C-DIC when lignin was amended; however, their DNA was derived from both inorganic and organic carbon sources rather than from inorganic carbon alone. Based on SIP results and supported by metagenomics, carbon transfer between catabolic and anabolic branches of metabolism is possible in these archaeal groups, indicating their anabolic versatility.

Conclusion: We provide evidence for the incorporation of the mixed organic and inorganic carbon by ANME-1 and Bathy-8 archaea in the environment. Video Abstract.