Summary C rocosphaera watsonii is a unicellular nitrogen ( N 2 )‐fixing cyanobacterium with ecological importance in oligotrophic oceans. In cultivated strains there are two phenotypes of C . watsonii (large and small cells) with differences that could differentially impact biogeochemical processes. Recent work has shown the phenotypes diverged through loss or addition of type‐specific genes in a fraction of their genomes, whe...

Summary The facultative symbiont of Riftia pachyptila , named here Candidatus Endoriftia persephone , has evaded culture to date, but much has been learned regarding this symbiosis over the past three decades since its discovery. The symbiont population metagenome was sequenced in order to gain insight into its physiology. The population genome indicates that the symbionts use a partial Calvin–Benson Cycle for carbon fixation...