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

Abstract

Marine N2-fixing cyanobacteria, including the unicellular genus Crocosphaera, are considered keystone species in marine food webs. Crocosphaera are 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, candidatus Crocosphaera waterburyi (C. waterburyi hereafter), enriched from the North Pacific Ocean, active in situ, and globally distributed in environmental datasets. C. waterburyi is morphologically, phylogenetically, and physiologically distinct from C. 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.