Abundance and activity of Chloroflexi-type SAR202 bacterioplankton in the meso- and bathypelagic waters of the (sub)tropical Atlantic

• Published in: Environmental Microbiology
• Main Authors: Varela, M.M. (Marta María), Van-Aken, H.M. (Hendrik M.), Herndl, G.J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Centro Oceanográfico de A Coruña 2008
• Subjects: North Atlantic
• Online Access: http://hdl.handle.net/10508/7641; https://doi.org/10.1111/j.1462-2920.2008.01627.x

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°N to 5°S). Fluorescence in situ hybridization (FISH) revealed that the overall abundance of SAR202 was ≤ 1 × 103 cells ml−1 in subsurface waters (100 m layer), increasing in the mesopelagic zone to 3 × 103 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 ≈ 0.03) to the deeper layers reaching a ratio of ∼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 ≈ 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. 6