The ecological role of pelagic methylotrophic bacteria assessed by high-resolution in situ analysis and autecology of isolated strains. Methylophilaceae bacterium B1 strain:MMS-10A-171 | isolate:'Candidatus Methylopumilus turicensis'

Methylotrophic planktonic bacteria fulfil particular roles in the carbon cycle of lakes by the turnover of C1 compounds. We studied two planktonic freshwater tribes (LD28 and PRD01a011B) affiliated with Methylophilaceae (Betaproteobacteria) in a multiphasic fashion. More than 120 axenic strains from these so far uncultivated lineages were isolated from the pelagial of Lake Zurich by dilution to extinction. Growth was enhanced upon addition of methanol and methylamine to sterile lake water and genomic analyses of two strains confirmed a methylotrophic lifestyle with a reduced set of genes involved in C1 metabolism. The very small and streamlined genomes (1.36 and 1.75 Mb) shared several pathways with the marine OM43 lineage. Phylogenetic analysis separated isolates into two distinct genotypes. As the closest described taxa (Methylotenera sp.) are only distantly related, we propose the establishment of a new genus with two species, i.e., ‘Candidatus Methylopumilus planktonicus’ and ‘Candidatus Methylopumilus turicensis’.