Current systems shape bacterial community structure in the Sanriku coastal area, northwestern Japan
Tokyo Univ. AORI
In the Sanriku coastal area (SCA), physicochemical and biological properties changed extensively between seasons, and a unique feature of this area is the seasonal transition of 3 major current systems, namely Oyashio, Kuroshio, and Tsugaru warm current. While it has been known that bacterial community structure changes with physicochemical properties and water mass in the ocean, the factors influencing their dynamics is poorly understood. Here we report spatiotemporal variability of bacterial community structures in the SCA based on 16S rRNA gene analysis. Observation under dynamic transition of current systems in combination with large data set generated by 454-pyrosequencing helps to determine key factors affecting the dynamics of oceanic bacterial communities. Surface waters collected at 5 stations during the cruises in 5 different seasons from 2012 to 2014 were sequentially filtered through a GF/A and 0.22 μm pore-size filters to collect particle-associated (PA) and free-living (FL) bacterial fractions respectively. DNA was extracted from the filters, and PCR amplification of bacterial 16S rRNA genes were subjected to pyrosequencing. Phylogenetic analysis indicated the dominance of Alphaproteobacteria especially SAR11 clade in FL fractions and bacteria affiliated with Bacteroidetes especially uncultured Flavobacteriacea groups in PA fractions. Redundancy analysis suggested that water temperature, salinity, DO, Chl.a, and phosphate explained the variation in bacterial community structures. Hierarchical clustering dendrogram showed that PA and FL bacterial communities in same current are closely related to each other even if they were collected in different seasons. This study provided a first insight into the composition of bacterial communities in the SCA. Furthermore, results of statistical analysis implied that the fluctuations in bacterial communities in the SCA depend on spatiotemporal changes in hydrographic regime and some specific environmental factors.
keywords:ocean,hydrography,bacteria,16S rRNA gene,pyrosequencing