Modulation of Nitrous Oxide (N₂O) Accumulation by Primary Metabolites in Denitrifying Cultures Adapting to Changes in Environmental C and N

Abstract

Metabolomics provides insights into the actual physiology of cells rather than their mere "potential", as provided by genomic and transcriptomic analysis. We investigate the modulation of nitrous oxide (NO) accumulation by intracellular metabolites in denitrifying bacteria using metabolomics and genome-based metabolic network modeling. Profiles of metabolites and their rates of production/consumption were obtained for denitrifying batch cultures under four conditions: initial COD:N ratios of 11:1 and 4:1 with and without nitrite spiking (28 mg-N L). Only the nitrite-spiked cultures accumulated NO. The NO spiked cultures with an initial COD:N = 11:1 accumulated 3.3 ± 0.57% of the total nitrogen added as NO and large pools of tricarboxylic acid cycle intermediates and amino acids. In comparison, the NO spiked cultures with COD:N = 4:1 showed significantly higher (p = 0.028) NO accumulation (8.5.3 ± 0.9% of the total nitrogen added), which was linked to the depletion of C11-C20 fatty acids. Metabolic modeling analysis shows that at COD:N of 4:1 the denitrifying cells slowly generate electron equivalents as FADH through β-oxidation of saturated fatty acids, while COD:N of 11:1 do it through the TCA cycle. When combined with NO shock, this prolonged the duration over which insufficient electron equivalents were available to completely reduce NOx to N, resulting in increased NO accumulation. Results extend the understanding of how organic carbon and nitrite loads modulate NO accumulation in denitrification, which may contribute to further design strategies to control greenhouse gas emissions from agricultural soils or wastewater treatment systems.

Unchanged nitrate and nitrite isotope fractionation during heterotrophic and Fe(II)-mixotrophic denitrification suggest a non-enzymatic link between denitrification and Fe(II) oxidation

“…This is further supported by previous NDFeO-based studies, which did not report any significant accumulation of N 2 O (and thus a possible inhibition of NosZ) (Kanaparthi et al, 2013;Ishii et al, 2016;Wang et al, 2016;Chen et al, 2018;Liu et al, 2018). Furthermore, considering that nitrite never accumulated in our experiments, inhibition of NosZ by nitrite (or free nitrous acid), as indicated by Perez-Garcia et al (2017), is also very unlikely.…”

Nitrogen Transformations and Microbial Characterization of Soils from Passive Nitrogen Removing Biofilters

“…Both carbon and O 2 regulate nitrous oxide reductase activity and the production of N 2 O relative to N 2 (Garcia et al 2017;Otte et al 1996). Because N 2 ─N production occurred continuously through these incubations, it is unlikely an ephemeral carbon limitation during preincubation led to the temporary accumulation of N 2 O inventories.…”

Biological Reduction of Nitric Oxide for Efficient Recovery of Nitrous Oxide as an Energy Source

“…■ DISCUSSION Synergistic Effect of NO Inhibition and Carbon Limitation on N 2 O Production. Previous studies have investigated the N 2 O accumulation profile and mechanism involved in NO 2 − -based denitrification, 30,64,65 but there is limited research on N 2 O accumulation during NO-based denitrification, which is composed of two steps: step (1) Fe(II)EDTA−NO → N 2 O, step (2) N 2 O → N 2 . NOR and N 2 OR are the key enzymes during the two steps and directly govern N 2 O accumulation.…”