Copper control of bacterial nitrous oxide emission and its impact on vitamin B12-dependent metabolism

Global agricultural emissions of the greenhouse gas nitrous oxide (N2O) have increased by around 20% over the last 100 y, but regulation of these emissions and their impact on bacterial cellular metabolism are poorly understood. Denitrifying bacteria convert nitrate in soils to inert di-nitrogen gas (N-2) via N2O and the biochemistry of this process has been studied extensively in Paracoccus denitrificans. Here we demonstrate that expression of the gene encoding the nitrous oxide reductase (NosZ), which converts N2O to N-2, is regulated in response to the extracellular copper concentration. We show that elevated levels of N2O released as a consequence of decreased cellular NosZ activity lead to the bacterium switching from vitamin B-12-dependent to vitamin B-12-independent biosynthetic pathways, through the transcriptional modulation of genes controlled by vitamin B-12 riboswitches. This inhibitory effect of N2O can be rescued by addition of exogenous vitamin B-12.