Cryptic Differentiation of a Genetically Monomorphic Marine Bacterial Population. Bacteria

The seemingly homogeneous seawater contains microspatial niches at the scale relevant to microbial activities. It remained poorly understood, however, whether these microenvironments are able to drive genome evolution of the microbial inhabitants. We show that two sympatric bacterial populations (the Marinobacterium population and the Roseobacter population ) from a single seawater sample display fundamentally different patterns of genome evolution. Our results indicate that phycospheres, where bacteria interact with phytoplankton, are likely the most important niche that drive the cryptic speciation of the Roseobacter population.