PROACTINOR · Single cell activity of prokaryotes assessed by MICRO-CARD-FISH in relation to bulk prokaryotic activity in the North Atlantic deep waters.

Final Activity Report Summary - PROACTINOR (Single cell activity of prokaryotes assessed by MICRO-CARD-FISH in relation to bulk prokaryotic activity in the North Atlantic deep waters.)

The distribution and activity of the bulk picoplankton community and, using microautoradiography combined with catalysed reported deposition fluorescence in situ hybridisation (MICRO-CARD-FISH), of the major prokaryotic groups (Bacteria, Crenarchaeota and Euryarchaeota) were determined in the water masses of the eastern North Atlantic. The bacterial contribution to total picoplankton abundance was fairly constant, comprising app. 50% of DAPI-stainable cells. Marine Euryarchaeota (group II) cells accounted always for <5% of DAPI-stainable cells. The percentage of total picoplankton identified as marine Crenarchaeota (group I) was app. 5% in subsurface waters and between 10 and 20% in the oxygen minimum layer and deep waters (North East Atlantic Deep Water [NEADW] and Lower Deep Water [LDW]). Leucine incorporation, as a measure of picoplankton activity, ranged between 8 to 0.003 pmol Leu L-1h-1, decreasing with depth by two orders of magnitude. Archaeal production generally followed the same decreasing trend with depth as the prokaryotic production, declining from 300 micromol C m-3 day-1 at the oxygen minimum layer to <5 micromol C m-3 day-1 in the mesopelagic waters. In the deep ocean (NEADW and LDW) inorganic carbon incorporation was generally <1 miromol C m-3 day-1 and at some stations we could not measure any inorganic carbon incorporation. Qualitative information using MICRO-CARD-FISH, showed that in the mesopelagic waters Crenarchaea was more active in taking up inorganic carbon (up to 53%) than Aspartic (Asp) acid. The oxygen minimum zone was the depth horizon where the lowest numbers of crenarchaeal cells taking up Asp was found. By contrast, the percentage of Crenarchaeota taking up D-Asp was highest in the LDW, while we could generally not found any [14C]-bicarbonate positive cells in the deep ocean (NEADW and LDW). These results suggest that Crenarchaeota are chemoautotrophic in the mesopelagic waters, using inorganic carbon as a carbon source and oxidising ammonia as an energy source, while in bathypelagic waters, Crenarchaeota are likely heterotrophs using efficiently D-amino acids. Single-cell activity, determined via a quantitative MICRO-CARD-FISH approach and, taking only substrate-positive cells into account, ranged from 0.05 to 0.5 amol of D-aspartic acid (Asp) cell-1 d-1 and 0.1 to 2 amol of L-Asp cell-1 d-1, slightly decreasing with depth. In contrast, the D-Asp:L-Asp cell-specific uptake ratio increased with depth. Finally, by combining data reported previously (Teira et al. a, b) and data from our study area, a pronounced latitudinal trend in the relative abundance of marine Crenarchaeota is apparent, decreasing towards the south (from 65 degrees N to 5 degrees S) in the eastern basin of the North Atlantic.Thus, the relative contribution of Crenarchaeota to deep water prokaryotic communities is more variable than previous studies have suggested and apparently related to large scale oceanic circulation patterns.

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