Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean

Significance Primary production generates a reservoir of dissolved organic carbon (DOC) in the ocean as large as the global inventory of atmospheric CO 2 . Once formed, DOC accumulates on timescales from less than 1 hour to millennia. Bacteria are important contributors to the respiration of DOC to CO 2 and the conversion of DOC to refractory biopolymers. Yet, the quantitative contribution of individual species within diverse consortia to DOC cycling remains unknown. We report that a single bacterial strain can consume as much DOC as diverse free-living microbial communities. This taxon is commonly observed in seawater when labile carbon is available, and may serve a key ecosystem function by rapidly recycling and regulating the level of DOC while also supporting ocean food webs.