Abstract
The abundance (based on catalyzed reporter deposition-fluorescence in situ hybrid ization, CARD-FISH) and leucine incorporation rates of Archaea and Bacteria were determined throughout the water column in the eastern Atlantic. Bacteria dominated throughout the water column, although their contribution to total prokaryotic abundance in the bathypelagic layer (1000 to 4000 m depth) was lower than in the surface and mesopelagic layers (0 to 1000 m depth). While marine Crenarchaeota Group I (MCG I) contributed 28 +/- 12% to the total prokaryotic abundance, with a generally higher contribution in the bathypelagic layer than in the surface and mesopelagic layers, marine Euryarchaeota Group II contributed < 5% throughout the water column. Using microautoradiography in combination with CARD-FISH, we tested the specificity of erythromycin and diphtheria toxin and found them to selectively inhibit bacterial and archaeal activity, respectively. These inhibitors were thus used to determine the contribution of Bacteria and Archaea to total leucine incorporation: Bacteria contributed 69 +/- 15%, and this value decreased with depth; Archaea contributed 32 +/- 16% over the entire water column, with no significant difference between surface and mesopelagic waters and the bathypelagic realm. The mean cell-specific leucine incorporation rate of MCG I (5.3 +/- 3.0 x 10(-20) mol cell(-1) d(-1)) was 3.5-fold lower than that of Bacteria (18.6 +/- 18.2 x 10(-20) mol cell(-1) d(-1)) in the surface and mesopelagic layer. In the bathypelagic layer, cell-specific leucine incorporation rates of Crenarchaeota were similar to those of Bacteria (2.3 x 10(-20) mol cell(-1) d(-1) for MCG I, 2.9 x 10(-20) mol cell(-1) d(-1) for Bacteria). In the surface and mesopelagic waters of the subtropical eastern North Atlantic, MCG I exhibited a lower heterotrophic activity on a per-cell level than Bacteria. In the bathypelagic zone, cell-specific heterotrophic activities of Bacteria and MCGI were similar.
Highlights
Mesophilic Archaea are ubiquitously present in all the major oceanic basins (Karner et al 2001, Teira et al 2006a, Kirchman et al 2007)
Erythromycin inhibits protein synthesis in Bacteria (Kohanski et al 2010) but should not affect archaeal protein synthesis, whereas diphtheria toxin inhibits protein synthesis in Archaea but does not affect Bacteria (Kessel & Klink 1980, Rohwer & Azam 2000). Using this dual inhibitor approach, we found that Archaea contribute on average 32% to the total prokaryotic leucine incorporation throughout the water column
Summing up the percentages of inhibition of leucine incorporation in the erythromycin- or streptomycintreated samples with that of the diphtheria toxintreated samples revealed that streptomycin apparently did not effectively inhibit bacterial leucine incorporation as the sum of the percentage of inhibition in streptomycin- and diphtheria toxin-treated samples were substantially lower than 100%
Summary
Mesophilic Archaea are ubiquitously present in all the major oceanic basins (Karner et al 2001, Teira et al 2006a, Kirchman et al 2007). Among the mesophilic marine Archaea, the marine Crenarchaeota Group I (MCG I, recently coined Thaumarchaeota; Brochier-Armanet et al 2008) are by far the most abundant archaeal group, accounting for about onethird of the total prokaryotic abundance in the waters. Quantitative PCR of the archaeal gene encoding the ammonia monooxygenase subunit A (amoA) indicates that the archaeal amoA gene abundance is orders of magnitude more abundant than bacterial amoA in oceanic waters (Mincer et al 2007, Agogué et al 2008, De Corte et al 2009), suggesting that MCG I might be more important for oceanic ammonia oxidation than Bacteria. Group- or even domain-specific ammonia oxidation measurements have not been reported to date
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