| Summary: | 14th International Symposium on Microbial Ecology (ISME14), 19-24 August 2012 Copenhagen, Denmark The Antarctic and Arctic regions offer a unique opportunity to test factors shaping the biogeography of marine microbial communities as they represent extremes in geographic separation yet share similar selection pressures. Here we report the most comprehensive comparison of bacterioplankton diversity between the polar oceans conducted to date, using standardized methods for pyrosequencing the V6 region of 16S rRNA gene. This effort included lower latitude ocean microbiomes to provide a global perspective for a global comparison of 837 844 sequence tags. Unexpectedly, we found a clear difference between Southern and Arctic Ocean microbiomes: 78.0% of the OTUs were unique to the Southern Ocean and 70.4% were unique to the Arctic Ocean. Even though polar ocean bacteria were more similar to each other than to lower latitude pelagic communities, analyses comparing depths, seasons and coastal versus open ocean demonstrated that Southern and Arctic Ocean bacterioplankton communities always clustered separately. Coastal surface Southern and Arctic Ocean communities were more dissimilar than open ocean communities. In contrast, deep ocean microbiomes were less different between poles and to lower latitude deep ocean waters, and they contained different patterns of diversity accumulation compared to surface, suggesting different mechanisms controlling surface and deep ocean community structures. We propose that surface bacterioplankton are more influenced by contemporary environmental conditions such as light, resource variability and climate, whereas deep communities are structured by a history of longer isolation and connectivity through ocean circulation. This work has identified major players in polar coastal and open ocean surface and deep communities, and provides a framework for understanding bacterioplankton biogeography Peer Reviewed
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