The environmental controls that govern the end product of bacterial nitrate respiration

• Published in: Science (American Association for the Advancement of Science) Vol. 345; no. 6197; pp. 676 - 679
• Main Authors: Kraft, Beate, Tegetmeyer, Halina E., Sharma, Ritin, Klotz, Martin G., Ferdelman, Timothy G., Hettich, Robert L., Geelhoed, Jeanine S., Strous, Marc
• Format: Journal Article
• Language: English
• Published: Washington American Association for the Advancement of Science 08.08.2014; The American Association for the Advancement of Science; AAAS
• Subjects: Amino acids; Ammonia; Aquatic ecosystems; Bacteria; BASIC BIOLOGICAL SCIENCES; Biogeochemistry; Carbon; Communities; Community Relations; Environmental Influences; Feedback (Response); Fermentation; Fertilizers; Inhalants; Metagenomics; Microorganisms; Nitrates; Nitrites; Nitrogen; Quaternary ammonium compounds; Respiration; Runoff; Sediments; Sulfides; Water quality
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1254070

In the biogeochemical nitrogen cycle, microbial respiration processes compete for nitrate as an electron acceptor. Denitrification converts nitrate into nitrogenous gas and thus removes fixed nitrogen from the biosphere, whereas ammonification converts nitrate into ammonium, which is directly reusable by primary producers. We combined multiple parallel long-term incubations of marine microbial nitrate-respiring communities with isotope labeling and metagenomics to unravel how specific environmental conditions select for either process. Microbial generation time, supply of nitrite relative to nitrate, and the carbon/nitrogen ratio were identified as key environmental controls that determine whether nitrite will be reduced to nitrogenous gas or ammonium. Our results define the microbial ecophysiology of a biogeochemical feedback loop that is key to global change, eutrophication, and wastewater treatment.