Anaerobic nitrite oxidation: a missing component of the marine nitrogen budget

Abstract: No organism can survive without nitrogen. The scarcity of fixed nitrogen in large surface areas of the ocean limits the capacity of phytoplankton to fix carbon dioxide. Nitrite oxidation retains nitrogen by oxidizing one fixed form of nitrogen, nitrite to the most abundant fixed nitrogen in the ocean, nitrate. Nitrite oxidation catalyzed by nitrite-oxidizing bacteria (NOB) is thought to be restricted to oxic waters. Surprisingly, we recovered draft genomes of NOB from anoxic seawaters via metagenomics. These NOB represent two novel species that are different from all known NOB. The novel NOB exclusively live in anoxic and suboxic seawaters where none of the canonical NOB are present. Due to sampling and experimental constraints, whether nitrite oxidation could occur anaerobically has been a long debate. We obtained the first direct evidence of anaerobic nitrite oxidation and demonstrated that nitrite oxidation (nitrogen retention) co- occurred with nitrogen loss. Implementing anaerobic nitrite oxidation in a biogeochemical model decreased the estimate of nitrogen loss by up to ~60%, suggesting the importance of this previously ignored nitrogen cycle process.

About this Series: The Atmospheres, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmospheres, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest. Contact: sacklunch-committee@mit.edu for more information and Zoom password