Anaerobic methanotroph 'Candidatus Methanoperedens nitroreducens' has a pleomorphic life cycle.

'Candidatus Methanoperedens' are anaerobic methanotrophic (ANME) archaea with global importance to methane cycling. Here meta-omics and fluorescence in situ hybridization (FISH) were applied to characterize a bioreactor dominated by 'Candidatus Methanoperedens nitroreducens' performing anaerobic methane oxidation coupled to nitrate reduction. Unexpectedly, FISH revealed the stable co-existence of two 'Ca. M. nitroreducens' morphotypes: the archetypal coccobacilli microcolonies and previously unreported planktonic rods. Metagenomic analysis showed that the 'Ca. M. nitroreducens' morphotypes were genomically identical but had distinct gene expression profiles for proteins associated with carbon metabolism, motility and cell division. In addition, a third distinct phenotype was observed, with some coccobacilli 'Ca. M. nitroreducens' storing carbon as polyhydroxyalkanoates. The phenotypic variation of 'Ca. M. nitroreducens' probably aids their survival and dispersal in the face of sub-optimal environmental conditions. These findings further demonstrate the remarkable ability of members of the 'Ca. Methanoperedens' to adapt to their environment.