AUTHOR=Detoni Amália Maria Sacilotto , Subramaniam Ajit , Haley Sheean T. , Dyhrman Sonya T. , Calil Paulo H. R. 

TITLE=Cyanobacterial Diazotroph Distributions in the Western South Atlantic

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.856643

DOI=10.3389/fmars.2022.856643

ISSN=2296-7745

ABSTRACT=<p>Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: <italic>Trichodesmium</italic>, <italic>Crocosphaera</italic>, UCYN-A, <italic>Richelia</italic> associated with <italic>Rhizosolenia</italic> (Het-1) or <italic>Hemiaulus</italic> (Het-2), and <italic>Calothrix</italic> associated with <italic>Chaetoceros</italic> (Het-3) was measured by quantitative PCR (qPCR) of the <italic>nifH</italic> gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using <italic>nifH</italic> gene copies as a proxy for phylotype abundance, <italic>Crocosphaera</italic> signals were the most abundant, with a broad distribution throughout the study region. <italic>Trichodesmium</italic> signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean.</p>