Evidence for the direct oxidation of organic nitrogen to N2 gas in the Arabian Sea

Abstract

We performed a suite of 15N incubations (15NO 2- , 15 NO 3 and 15NH4+) with and without the organic-nitrogen (N) compound allylthiourea (ATU), in the suboxic waters of the Arabian Sea. Production of 29N2 in control (-ATU) incubations with either 15NH4+14NO2- , or their analogues, 15NO2-14NH4+, though small, confirmed the presence of anammox. In contrast, when we added ATU, along with 15NO2- and 14NH 4+, there was a much greater production of 29N2, with 92% of the 15 N-label being recovered as 29N2 on average. Such stimulated production of 29N2 could not be due to anammox, as the addition of ATU, along with 15NH4+14NO 2-, only produced 29N2 equivalent to that in the controls. The ratios of 29N2 to 30N2 produced also precluded stimulation of denitrification. We present this as evidence for a hitherto uncharacterised metabolism potentially capable of oxidising organic-N (e.g. NH2 groups) directly to N2 gas at the expense of NO2. © 2012 International Society for Microbial Ecology All rights reserved.