Influence of nitrogen-fixation on microbial community gene expression in the oligotrophic Southwest Pacific Ocean

Marine bacterioplankton play key roles in the carbon and nitrogen cycles, comprising a significant proportion of biomass in surface waters of the oligotrophic ocean, consuming about half of all primary production, and remineralizing organic matter into inorganic compounds. The fluxes of carbon and organic matter in planktonic communities are controlled by the availability of nutrients. Nitrogen is believed to be one of the primary limiting nutrients in many regions of the ocean. Atmospheric nitrogen is available to nitrogen-limited microbial communities through biological nitrogen fixation, which is performed by a limited number of taxa in the open ocean. Metatranscriptomic samples were collected along a North-South transect in the western South Pacific Ocean, to investigate the relationship between nitrogen-fixing populations and microbial community gene expression in the nitrogen-limited oligotrophic water. Nitrogen-fixer abundance in the region is variable, with blooms and surface aggregations of dominant unicellular and filamentous taxa. Thus, the southwest Pacific region represents an ideal study location for understanding microbial community gene expression as a function of nitrogen limitation and presence of different groups of nitrogen-fixing microorganisms.

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