title: Abundance and activity of Chloroflexi-type SAR202 bacterioplankton in the meso- and bathypelagic waters of the (sub)tropical Atlantic.
abstract: The contribution of Chloroflexi-type SAR202 cells to total picoplankton and bacterial abundance and uptake of D- and L-aspartic acids (Asp) was determined in the different meso- and bathypelagic water masses of the (sub)tropical Atlantic (from 35 degrees N to 5 degrees S). Fluorescence in situ hybridization (FISH) revealed that the overall abundance of SAR202 was < or = 1 x 10(3) cells ml(-1) in subsurface waters (100 m layer), increasing in the mesopelagic zone to 3 x 10(3) cells ml(-1) and remaining fairly constant down to 4000 m depth. Overall, the percentage of total picoplankton identified as SAR202 increased from < 1% in subsurface waters to 10-20% in the bathypelagic waters. On average, members of the SAR202 cluster accounted for about 30% of the Bacteria in the bathypelagic waters, whereas in the mesopelagic and subsurface waters, SAR202 cells contributed < 5% to total bacterial abundance. The ratio of D-Asp : L-Asp uptake by the bulk picoplankton community increased from the subsurface layer (D-Asp : L-Asp uptake ratio approximately 0.03) to the deeper layers reaching a ratio of approximately 1 at 4000 m depth. Combining FISH with microautoradiography to determine the proportion of SAR202 cells taking up D-Asp versus L-Asp, we found that approximately 30% of the SAR202 cells were taking up L-Asp throughout the water column while D-Asp was essentially not taken up by SAR202. This D-Asp : L-Asp uptake pattern of SAR202 cells is in contrast to that of the bulk bacterial and crenarchaeal community in the bathypelagic ocean, both sustaining a higher fraction of D-Asp-positive cells than L-Asp-positive cells. Thus, although the Chloroflexi-type SAR202 constitutes a major bathypelagic bacterial cluster, it does not contribute to the large fraction of d-Asp utilizing prokaryotic community in the meso- and bathypelagic waters of the North Atlantic, but rather utilizes preferentially L-amino acids.
authors.affiliation: Department of Biological Oceanography, NOIZ Royal Netherlands Institute for Sea Research, PO BOX 59, 1790 AB Den Burg, the Netherlands.
authors.forename: Marta M
authors.initials: MM
authors.lastname: Varela
authors.forename: Hendrik M
authors.initials: HM
authors.lastname: van Aken
authors.forename: Gerhard J
authors.initials: GJ
authors.lastname: Herndl
mesh_terms: D041862:Chloroflexi / Q000254:growth & development / Q000378:metabolism*; D026603:D-Aspartic Acid / Q000096:biosynthesis / Q000378:metabolism; D004269:DNA, Bacterial / Q000032:analysis; D017404:In Situ Hybridization, Fluorescence; D008386:Marine Biology; D010933:Plankton / Q000254:growth & development; D012623:Seawater / Q000382:microbiology*
chemical_list: D004269:DNA, Bacterial; D026603:D-Aspartic Acid