A snapshot on spatial and vertical distribution of bacterial communities in the eastern Indian Ocean

Besides being critical components of marine food web, microorganisms play vital roles in biogeochemical cycling of nutrients and elements in the ocean. Currently little is known about microbial population structure and their distributions in the eastern Indian Ocean. In this study, we applied molecular approaches including polymerase chain reaction-denaturant gradient gel electrophoresis (PCR-DGGE) and High-Throughput next generation sequencing to investigate bacterial 16S rRNA genes from the equatorial regions and the adjacent Bay of Bengal in the eastern Indian Ocean. In general, Bacteroidetes, Proteobacteria (mainly Alpha, and Gamma), Actinobacteria, Cyanobacteria and Planctomycetes dominated the microbial communities. Horizontally distinct spatial distribution of major microbial groups was observed from PCR-DGGE gel image analyses. However, further detailed characterization of community structures by pyrosequencing suggested a more pronounced stratified distribution pattern: Cyanobacteria and Actinobacteria were more predominant at surface water (25 m); Bacteroidetes dominated at 25 m and 150 m while Proteobacteria (mainly Alphaproteobacteria) occurred more frequently at 75 m water depth. With increasing water depth, the bacterial communities from different locations tended to share high similarity, indicating a niche partitioning for minor groups of bacteria recovered with high throughput sequencing approaches. This study provided the first "snapshot" on biodiversity and spatial distribution of Bacteria in water columns in the eastern Indian Ocean, and the findings further emphasized the potential functional roles of these microbes in energy and resource cycling in the eastern Indian Ocean