In this study, we investigated the bacterial diversity in the surface microlayer (<1 mm) and its corresponding subsurface layer (0.5 m in depth) and compared their bacterial communities in seven sites located across the northern Yellow Sea and Bohai Sea in China. Bacterial cell abundance was determined by flow cytometry; the structure of the bacterial assemblage was quantitatively assessed through denaturing gradient gel electrophoresis. Bacterial cell abundant was not significantly different between bacterioneuston and bacterioplankton. The colony-forming units in the surface microlayer were significantly enriched compared with that in the subsurface layer. Enrichment factors (the ratio of abundance in the surface layer to that in the subsurface layer) led to high total cell counts in the surface microlayer of the cultivated bacteria (46.92 and 1.28 for colony-forming units and cells, respectively). The fraction of neustonic bacteria was similar among the sites, despite large differences in environmental conditions. Moreover, the community structures of bacterioneuston and bacterioplankton exhibited distinct and consistent differences.

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