title: Clarifying the regulation of NO/N2O production in Nitrosomonas europaea during anoxic-oxic transition via flux balance analysis of a metabolic network model.
abstract: The metabolic mechanism regulating the production of nitric and nitrous oxide (NO, N2O) in ammonia oxidizing bacteria (AOB) was characterized by flux balance analysis (FBA) of a stoichiometric metabolic network (SMN) model. The SMN model was created using 51 reactions and 44 metabolites of the energy metabolism in Nitrosomonas europaea, a widely studied AOB. FBA of model simulations provided estimates for reaction rates and yield ratios of intermediate metabolites, substrates, and products. These estimates matched well, deviating on average by 15% from values for 17 M yield ratios reported for non-limiting oxygen and ammonium concentrations. A sensitivity analysis indicated that the reactions catalysed by cytochromes aa3 and P460 principally regulate the pathways of NO and N2O production (hydroxylamine oxidoreductase mediated and nitrifier denitrification). FBA of simulated N. europaea exposure to oxic-anoxic-oxic transition indicated that NO and N2O production primarily resulted from an intracellular imbalance between the production and consumption of electron equivalents during NH3 oxidation, and that NO and N2O are emitted when the sum of their production rates is greater than half the rate of NO oxidation by cytochrome P460.
authors.affiliation: Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
authors.forename: Octavio
authors.initials: O
authors.lastname: Perez-Garcia
authors.affiliation: Centre for Microbial Innovation, School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
authors.forename: Silas G
authors.initials: SG
authors.lastname: Villas-Boas
authors.affiliation: Department of Molecular Medicine and Pathology, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
authors.forename: Simon
authors.initials: S
authors.lastname: Swift
authors.affiliation: Department of Earth and Environmental Engineering, Columbia University, 500 West 120 Street, New York, USA.
authors.forename: Kartik
authors.initials: K
authors.lastname: Chandran
authors.affiliation: Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Electronic address: n.singhal@auckland.ac.nz.
authors.forename: Naresh
authors.initials: N
authors.lastname: Singhal
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D058440:Denitrification; D064688:Metabolic Flux Analysis; D053858:Metabolic Networks and Pathways; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism*; D043370:Nitrosomonas europaea / Q000378:metabolism*; D009609:Nitrous Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D009569:Nitric Oxide; D009609:Nitrous Oxide
keywords: Ammonia oxidizing bacteria; Flux balance analysis; Metabolic network modelling; Nitrifier denitrification; Nitrosomonas europaea metabolism; Nitrous oxide production