1 research outputs found
Modulation of Nitrous Oxide (N<sub>2</sub>O) Accumulation by Primary Metabolites in Denitrifying Cultures Adapting to Changes in Environmental C and N
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 (N<sub>2</sub>O) 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<sup>–1</sup>). Only the nitrite-spiked cultures
accumulated N<sub>2</sub>O. The NO<sub>2</sub><sup>–</sup> spiked
cultures with an initial COD:N = 11:1 accumulated 3.3 ± 0.57%
of the total nitrogen added as N<sub>2</sub>O and large pools of tricarboxylic
acid cycle intermediates and amino acids. In comparison, the NO<sub>2</sub><sup>–</sup> spiked cultures with COD:N = 4:1 showed
significantly higher (p = 0.028) N<sub>2</sub>O 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<sub>2</sub> through β-oxidation
of saturated fatty acids, while COD:N of 11:1 do it through the TCA
cycle. When combined with NO<sub>2</sub><sup>–</sup> shock,
this prolonged the duration over which insufficient electron equivalents
were available to completely reduce NOx to N<sub>2</sub>, resulting
in increased N<sub>2</sub>O accumulation. Results extend the understanding
of how organic carbon and nitrite loads modulate N<sub>2</sub>O accumulation
in denitrification, which may contribute to further design strategies
to control greenhouse gas emissions from agricultural soils or wastewater
treatment systems