A novel, N2-fixing cyanobacterium present and active in the global oceans

Abstract

AbstractMarine N2-fixing cyanobacteria, including the unicellular genusCrocosphaera, are considered keystone species in marine food webs.Crocosphaeraare globally distributed and provide new sources of nitrogen (N) and carbon (C), which fuel oligotrophic microbial communities and upper trophic levels. Despite their ecosystem importance, only one species,Crocosphaera watsonii, has ever been identified and characterized as widespread in the oligotrophic oceans. Herein, we present a novel species, candidatusCrocosphaera waterburyi(C. waterburyihereafter), enriched from the North Pacific Ocean, activein situ, and globally distributed in environmental datasets.C. waterburyiis morphologically, phylogenetically, and physiologically distinct fromC. watsonii; therefore, description of this novel species provides a new window into previously uncharacterized diversity and ecology of unicellular N2-fixing cyanobacterial taxa and further highlights their importance in the global N cycle.