OB19 Moving beyond Trichodesmium: assessing the importance of non-cyanobacterial diazotrophs and other previously overlooked nitrogen-fixers in marine ecosystems

We’re glad to announce our non-cyanobacterial diazotroph hybrid session at OSM22 (abstract below). Please consider submitting an abstract by 29 September, 11:59 pm Eastern Daylight Time and spread the word!
 Mar Benavides and all

Through the 20th century, nitrogen fixation in the oceans was thought to be dominated by large, filamentous cyanobacteria, including the colony-forming Trichodesmium and heterocyst-forming symbionts of diatoms. Recent sequencing-based approaches have radically shifted this paradigm, highlighting the importance of other nitrogen-fixers (called diazotrophs) in diverse marine environments, including the water column and also the benthos (e.g. sediments and nitrogen-fixing symbionts of corals). Furthermore, it has been suggested that non-cyanobacterial diazotrophs (NCDs) may be numerically more important than their cyanobacterial counterparts, even in open ocean environments. NCDs are a phylogenetically diverse group of microbes that fundamentally differ from cyanobacteria in that they are putative heterotrophs and thus likely require exogenous fixed carbon. Despite the recurrent recovery of NCD genes in PCR-based and metagenomic ocean surveys, little is known about the physiological diversity and ecology of these organisms and whether they actively contribute to nitrogen fixation in marine systems. Recent reports of nitrogen fixation in unexpected environments, including coastal upwelling systems, high latitude oceans, mesopelagic waters, and symbiotic systems, underscore the need to understand the taxa responsible for marine nitrogen fixation in order to better constrain this keystone process.

This session strives to shed light on previously overlooked nitrogen-fixers, in effort to better understand the important players driving global marine nitrogen fixation rates. We encourage submissions that apply novel technical approaches to investigating the distribution and activity of these rare biosphere microbes, including stable isotope probing, gene-based surveys, ‘omics tools, visualization-based techniques, and cultivation or model-based approaches.