Bacterial Circuits of Nitrous Oxide Production Characterized Using Metabolic Network Modelling and Metabolomics

Metabolic network modelling and metabolomics are computational and analytical techniques used to characterize the flow of compounds and energy within metabolic pathways of microbes. This paper illustrates the application of such techniques to explain how different environmental conditions of biological nitrogen removal (BNR) processes trigger the production and emission of nitrous oxide (N2O) - a greenhouse gas and ozone depletion substance - by nitrifying and denitrifying microbes. 

The research approach is exemplified by analysing N2O production in laboratory scale BNR systems by: (i) pure nitrifying species and (ii) mixed nitrifying cultures. The pure cultures (Nitrosomonas europaea) simulations shows that N2O is produced due to electron flow imbalances in nitrifying cells, and that electron carriers play a key role by distributing electron equivalents to N2O and NO formation reactions. The mixed culture simulations reveal two key aspects of N2O formation in nitrifying microbial communities: (i) microbes can lower N2O emissions by dissipating NO (a N2O precursor molecule); and (ii) the structure (i.e. the richness and abundance of species) of the microbial community influences the amount of N2O produced and emitted. 

This study concludes that operational conditions that promote imbalances between the cell’s electron donors and electron acceptors cause N2O formation. Specifically, in nitrification processes, a build-up of electron donors leads to N2O formation. This paper demonstrates the unique features of metabolic modelling procedures and metabolomics by applying these to obtain insight into microbial functioning in wastewater treatment processes.