Aerobic denitrification as an N2O source from microbial communities

Author:

Roothans Nina1ORCID,Gabriëls Minke1,Abeel Thomas234ORCID,Pabst Martin1ORCID,van Loosdrecht Mark C M1ORCID,Laureni Michele15ORCID

Affiliation:

1. Department of Biotechnology, Delft University of Technology , van der Maasweg 9, 2629 HZ Delft , the Netherlands

2. Delft Bioinformatics Lab, Delft University of Technology, van Mourik Broekmanweg 6, Delft 2628 XE , the Netherlands

3. Infectious Disease and Microbiome Program , Broad Institute of MIT and Harvard, , United States

4. 415 Main Street, Cambridge, MA 02142 , Broad Institute of MIT and Harvard, , United States

5. Department of Water Management, Delft University of Technology, Stevinweg 1, 2628 CN Delft , the Netherlands

Abstract

Abstract Nitrous oxide (N2O) is a potent greenhouse gas of primarily microbial origin. Oxic and anoxic emissions are commonly ascribed to autotrophic nitrification and heterotrophic denitrification, respectively. Beyond this established dichotomy, we quantitatively show that heterotrophic denitrification can significantly contribute to aerobic nitrogen turnover and N2O emissions in complex microbiomes exposed to frequent oxic/anoxic transitions. Two planktonic, nitrification-inhibited enrichment cultures were established under continuous organic carbon and nitrate feeding, and cyclic oxygen availability. Over a third of the influent organic substrate was respired with nitrate as electron acceptor at high oxygen concentrations (>6.5 mg/L). N2O accounted for up to one-quarter of the nitrate reduced under oxic conditions. The enriched microorganisms maintained a constitutive abundance of denitrifying enzymes due to the oxic/anoxic frequencies exceeding their protein turnover—a common scenario in natural and engineered ecosystems. The aerobic denitrification rates are ascribed primarily to the residual activity of anaerobically synthesised enzymes. From an ecological perspective, the selection of organisms capable of sustaining significant denitrifying activity during aeration shows their competitive advantage over other heterotrophs under varying oxygen availabilities. Ultimately, we propose that the contribution of heterotrophic denitrification to aerobic nitrogen turnover and N2O emissions is currently underestimated in dynamic environments.

Funder

Stichting Toegepast Onderzoek Waterbeheer

Hoogheemraadschap Hollands Noorderkwartier

Waterschap de Dommel

Dutch Research Council

Publisher

Oxford University Press (OUP)

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