Influence of copper on expression of nirS , norB and nosZ and the transcription and activity of NIR , NOR and N 2 OR in the denitrifying soil bacteria Pseudomonas stutzeri

Summary Reduction of the potent greenhouse gas nitrous oxide (N 2 O) occurs in soil environments by the action of denitrifying bacteria possessing nitrous oxide reductase (N 2 OR ), a dimeric copper (Cu)‐dependent enzyme producing environmentally benign dinitrogen (N 2 ). We examined the effects of increasing Cu concentrations on the transcription and activity of nitrite reductase ( NIR ), nitric oxide reductase ( NOR ) and N 2 OR in Pseudomonas stutzeri grown anaerobically in solution over a 10‐day period. Gas samples were taken on a daily basis and after 6 days, bacterial RNA was recovered to determine the expression of nirS , norB and nosZ encoding NIR , NOR and N 2 OR respectively. Results revealed that 0.05 mM Cu caused maximum conversion of N 2 O to N 2 via bacterial reduction of N 2 O. As soluble Cu generally makes up less than 0.001% of total soil Cu, extrapolation of 0.05 mg l −l soluble Cu would require soils to have a total concentration of Cu in the range of, 150–200 μg g −1 to maximize the proportion of N 2 O reduced to N 2 . Given that many intensively farmed agricultural soils are deficient in Cu in terms of plant nutrition, providing a sufficient concentration of biologically accessible Cu could provide a potentially useful microbial‐based strategy of reducing agricultural N 2 O emissions.