Contribution of Crenarchaeota and Euryarchaeota to the prokaryotic plankton in the coastal northwestern Black Sea

The NW Black Sea is an area with peculiar hydrological, hydrochemical and biological features (river plume dynamics, coastal upwelling, intense eutrophication, blooms algae). We determined the abundance and distribution of the two major groups of Archaea (Crenarchaeota and Euryarchaeota) in three contrasting sites of the NW Black Sea from May to August 2004 to estimate the contribution of non-extremophilic Archaea to the coastal prokaryotic plankton. Using catalyzed reporter deposition-fluorescence in situ hybridization, Euryarchaeota were found to be particularly prominent (11-22% of total prokaryotic plankton) in the low-salinity waters during late-spring and summer, whereas Crenarchaeota contributed only ∼5% to the prokaryotic community in these waters. The abundance of Crenarchaeota was highest in nutrient- and particle-rich waters and lowest in offshore Black Sea surface waters. These results confirm recent studies on the distribution of planktonic Archaea with Euryarchaeota dominating the archaeal community in surface waters. Statistical analyses indicated significant correlations between crenarchaeotal abundance, ammonia and nitrate concentrations at each sites. Our data show that the archaeal plankton constitute an important and dynamic component of the prokaryotic plankton in the coastal oxygenated waters of the NW Black Sea and might play a significant role in the nitrogen cycle.