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A Network Biology Approach to Denitrification in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a metabolically flexible member of the Gammaproteobacteria. Under anaerobic conditions and the presence of nitrate, P. aeruginosa can perform (complete) denitrification, a respiratory process of dissimilatory nitrate reduction to nitrogen gas via nitrite ($NO_{2}$), nitric oxide ($NO$) and nitrous oxide ($N_{2}O$). This study focuses on understanding the influence of environmental conditions on bacterial denitrification performance, using a mathematical model of a metabolic network in P. aeruginosa. To our knowledge, this is the first mathematical model of denitrification for this bacterium. Analysis of the long-term behavior of the network under changing concentration levels of oxygen ($O_{2}$), nitrate ($NO_{3}$), and phosphate ($PO_{4}$) suggests that $PO_{4}$ concentration strongly affects denitrification performance. The model provides five predictions on denitrification activity of P. aeruginosa under various environmental conditions, and these predictions are either experimentally validated or supported by pertinent biological literature. One motivation for this study is to capture the effect of $PO_{4}$ on a denitrification metabolic network of P. aeruginosa in order to shed light on mechanisms for greenhouse gas $N_{2}O$ accumulation during seasonal oxygen depletion in aquatic environments such as Lake Erie (Laurentian Great Lakes, USA).