Anomalously high abundance of Crocosphaera in the South Pacific Gyre.

The unicellular diazotrophic cyanobacterium Crocosphaera contributes significantly to fixed nitrogen inputs in the oligotrophic ocean. In the western tropical South Pacific Ocean (WTSP), these diazotrophs abound thanks to the phosphorus-rich waters provided by the South Equatorial Current, and iron provided aeolian and subsurface volcanic activity. East of the WTSP, the South Pacific Gyre (SPG) harbors the most oligotrophic and transparent waters of the world's oceans, where only heterotrophic diazotrophs have been reported before.

Overlooked and widespread pennate diatom-diazotroph symbioses in the sea.

Persistent nitrogen depletion in sunlit open ocean waters provides a favorable ecological niche for nitrogen-fixing (diazotrophic) cyanobacteria, some of which associate symbiotically with eukaryotic algae. All known marine examples of these symbioses have involved either centric diatom or haptophyte hosts. We report here the discovery and characterization of two distinct marine pennate diatom-diazotroph symbioses, which until now had only been observed in freshwater environments.

Evaluation of argon-induced hydrogen production as a method to measure nitrogen fixation by cyanobacteria.

The production of dihydrogen (H ) is an enigmatic yet obligate component of biological dinitrogen (N ) fixation. This study investigates the effect on H production by N fixing cyanobacteria when they are exposed to either air or a gas mixture consisting of argon, oxygen, and carbon dioxide (Ar:O :CO ). In the absence of N , nitrogenase diverts the flow of electrons to the production of H , which becomes a measure of Total Nitrogenase Activity (TNA).