Archaeal uptake of enantiomeric amino acids in the meso- and bathypelagic waters of the North Atlantic

We determined the contribution of the three major prokaryotic groups (Bacteria, Crenarchaeota, and Euryarchaeota) on the uptake of D- and L-aspartic acid (Asp) in the major water masses of the North Atlantic (from 100-to 4,000-m depth) with the use of microautoradiography combined with catalyzed reporter deposition fluorescence in situ hybridization (MICRO-CARD-FISH). The percentage of prokaryotic cells that assimilated D- and L-Asp ranged from <5% to 25%. In the meso- and bathypelagic waters of the North Atlantic, Archaea are more abundant (42% ± 2% of 4′,6′-diamino-2-phenylindole [DAPI]-stained cells) than Bacteria (30% ± 1% of DAPI-stained cells), and more archaeal than bacterial cells are actively incorporating D-Asp (62% ± 2% vs. 38% ± 2% of total D-Asp active cells). In contrast, Bacteria and Archaea almost equally contribute to L-Asp use in the deep waters of the North Atlantic (47% ± 2% vs. 53% ± 2% of total L-Asp active cells). The increase in the D-Asp:L-Asp uptake ratio in the prokaryotic community with depth appears to be driven by the efficient uptake of D-Asp by, especially, the Crenarchaeota in the deep waters. Because Archaea, and particularly Crenarchaeota, commonly dominate the prokaryotic communities in the ocean's interior, we suggest that they represent a previously unrecognized sink of D-amino acids in the deep ocean.