Program

Nitrogen (N) is a primary limiting factor for microbial growth and productivity in much of the ocean. Microbes have evolved diverse N utilization strategy and regulate N cycling in the ocean. To make a deep understanding of microbial community structure and their N utilization strategy in different N regimes of the ocean, we investigated microbial diversity and expressions of N-utilizing genes in different N regimes of the Western Pacific Ocean using a combination of high-throughput sequencing and relative qPCR technologies. The results showed that cyanobacterium, Prochlorococcus dominated the microbial population in the oligotrophic Northwestern Pacific region, and the unicellular cyanobacterium_UCYN-A was the primary N2-fixing microorganism in N-deficient region. Normalized transcripts of urea transporter (urtA) gene presented the highest expression in N-deficient surface seawater, which was consistent with the abundance of Prochlorococcus. On the contrary, expression of Synechococcus NarB gene in oligotrophic surface seawater was much lower than that of urtA gene, and its expression was high in eutrophic regions, especially in DCM layers. Our study indicates that Prochlorococcus mediating urea metabolism was the principal N assimilation process in the oligotrophic regime, while nitrate assimilation was the major N utilization way in the eutrophic regime, particularly in nutritious DCM layers.