TEFLON BACTERIA? PELAGIBACTER UBIQUE, THE MOST ABUNDANT BACTERIUM IN THE OCEAN, SLIPS THROUGH SUSPENSION FEEDERS MUCUS NETS

Marine suspension feeders use biological filters to handle thousands of particles simultaneously. Biological filtration has major influence on planktonic microbial communities composition, and hence, on their contribution to biogeochemical cycles in the ocean. Grazing resistance is expected to be a major factor determining microbe success at the community level, however, information regarding microbe specific grazing in the ocean is meager. We use a combination of underwater sampling techniques, flow cytometry, qPCR, fluorescent microscopy, CARD-FISH, and next generation sequencing to measure specific microbial grazing rate, at the phylotype level. Our data shows that several bacteria strains, mainly the photosynthetic cyanobacteria Prochlorococcus, and Synechococcus that comprised 29-46% of total bacteria were removed at high rates by both pelagic tunicates (appendicularians) and benthic tunicates (ascidians). Surprisingly, dominant non-photosynthetic bacteria, in particular, members of the SAR11 clade that comprised 31-48% of total bacteria, were removed at a much lower efficiency. To test the hypothesis that different surface properties provides the ability to avoid grazing, we used affinity chromatography to compare the hydrophobicity index of natural and cultured bacteria phylotype. Columns experiments revealed that pelagibacter ubique of the SAR11 clade has significantly different surface properties then all other bacteria tested. Based on these results, we speculate that a guild of free-living bacteria, most notably the SAR11 clade, have given up the ability to stick to nutrient rich organic particles in return to a non-sticky, Teflon-like, cell surface that confer them resistance to grazing by mucus suspension feeders and contribute to their phenomenal success in the ocean.