Abstract
In this study, we used 454-pyrosequencing to report the highly diverse diazotroph communities in the Kuroshio and its adjacent waters along a transect across the Tokara Strait, Japan. Terrestrial input from the islands resulted in a highly heterogeneous diazotroph community within a relatively small geographic region, which was presumably caused by the remarkably different responses of UCYN-A2, UCYN-C and Trichodesmium to the steep environmental gradient. On the other hand, most major cyanobacterial OTUs found in this study were also detected in an unpublished dataset from the upstream Kuroshio, which suggests transportation of diazotrophs by the Kuroshio in large geographic scale. A significant amount of UCYN-C was found in the Kuroshio and offshore stations, suggesting the importance of this potentially overlooked group in the western North Pacific Ocean (WNPO). Moreover, a novel sublineage of UCYN-B was defined, which was predominant in an oligotrophic water sample; and it was also found to be widely distributed in oceanic waters. In addition, the apparent increase in relative abundance of UCYN-A2 from offshore to near-shore water provides evidence for the earlier and under-debating view that UCYN-A2 prefers coastal conditions. Our report provides new knowledge for understanding the phylogeny and ecology of unicellular cyanobacterial diazotrophs in WNPO.
Highlights
Biological nitrogen fixation is an important source of new nitrogen input in the subtropical and tropical oceans [1,2,3], where bioavailable nitrogen is usually a major limiting factor for primary production
According to the surface current data from the ship-mounted acoustic Doppler current profiler (ADCP) and the path of Kuroshio Current (KC) from the “Quick Bulletin of Ocean Conditions” provided by the Japan Coast Guards (S1 Fig), ST.3 was located in the core of KC, and ST.4 was located in the boundary of KC
The highest sea surface temperature occurred at ST.3, which was at the core of the KC, and the lowest temperature was observed at ST.6 (Fig 1, Table 2)
Summary
Biological nitrogen fixation is an important source of new nitrogen input in the subtropical and tropical oceans [1,2,3], where bioavailable nitrogen is usually a major limiting factor for primary production. Biological nitrogen fixation is carried out by a group of prokaryotes, called diazotrophs. Trichodesmium was initially believed to be the major diazotroph in the oceans [4]. With the development of molecular techniques, and the nifH gene (which encodes a nitrogenase subunit), becoming a commonly-used phylogenetic biomarker of the diazotrophs [5], a diverse range of microbes has since been discovered.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
