Respiration-driven methanotrophic growth of diverse marine methanogens

Anaerobic marine environments are the third largest producer of the greenhouse gas methane. The release to the atmosphere is prevented by anaerobic 'methanotrophic archaea (ANME) dependent on a symbiotic association with sulfate-reducing bacteria or direct reduction of metal oxides. Metagenomic analyses of ANME are consistent with a reverse methanogenesis pathway, although no wild-type isolates have been available for validation and biochemical investigation. Herein is reported the characterization of methanotrophic growth for the diverse marine methanogens Methanosarcina acetivorans C2A and Methanococcoides orientis sp. nov. Growth was dependent on reduction of either ferrihydrite or humic acids revealing a respiratory mode of energy conservation. Acetate and/or formate were end products. Reversal of the well-characterized methanogenic pathways is remarkably like the consensus pathways for uncultured ANME based on extensive metagenomic analyses.

Automated summary

Anaerobic marine environments play a significant role in the production of methane, a greenhouse gas. Methanotrophic archaea (ANME) prevent methane release by relying on a symbiotic relationship with sulfate-reducing bacteria or direct reduction of metal oxides. This study examines the growth characteristics of two marine methanogens and reveals that they can conserve energy by reducing ferrihydrite or humic acids, resulting in the production of acetate and/or formate.