Emergence and disruption of cooperativity in a denitrifying microbial community

Anthropogenic perturbations to the nitrogen cycle, primarily through use of synthetic fertilizers, is driving an unprecedented increase in the emission of nitrous oxide (N ₂ O), a potent greenhouse gas and an ozone depleting substance, causing urgency in identifying the sources and sinks of N ₂ O. Microbial denitrification is a primary contributor to biotic production of N ₂ O in anoxic regions of soil, marine systems, and wastewater treatment facilities. Here, through comprehensive genome analysis, we show that pathway partitioning is a ubiquitous mechanism of complete denitrification within microbial communities. We have investigated mechanisms and consequences of process partitioning of denitrification through detailed physiological characterization and kinetic modeling of a synthetic community of Rhodanobacter R12 and Acidovorax 3H11 . We have discovered that these two bacterial isolates, from a heavily nitrate (NO ₃ ⁻ ) contaminated superfund site, complete denitrification through the exchange of nitrite (NO ₂ ⁻ ) and nitric oxide (NO). The process partitioning of denitrification and other processes, including amino acid metabolism, contribute to increased cooperativity within this denitrifying community. We demonstrate that certain contexts, such as high NO ₃ ⁻ , cause unbalanced growth of community members, due to differences in their substrate utilization kinetics. The altered growth characteristics of community members drives accumulation of toxic NO ₂ ⁻ , which disrupts denitrification causing N ₂ O off gassing.