Hemiaulus-Richelia physiological response to different nitrogen sources

Diatom-diazotroph associations (DDAs) play an important role at the base of the food web by fixing both carbon dioxide and nitrogen gas into organic matter. The ability of DDAs to fix nitrogen allows the relatively large diatom host to survive under nitrogen-deplete conditions and, thus, contribute significantly to organic carbon export in oligotrophic waters. Yet, relatively little is known about this symbiosis, in part because it has historically been difficult to maintain DDAs in culture. Here, we isolated the DDA Hemiaulus-Richelia from the Sargasso Sea and developed a protocol to maintain it in laboratory culture for long time periods (years). Experiments were conducted to determine how Hemiaulus-Richelia responds to different nitrogen sources with measurements of growth and nitrogen fixation.