Promoter Sequences Do Not Solely Govern nosZ Expression Differences between Bradyrhizobium ottawaense and B....

Nitrous oxide (N₂O) is a potent greenhouse gas, and the enzyme Nos catalyzes its reduction to dinitrogen (N₂). Bradyrhizobium ottawaense exhibits strong N₂O-reducing activity with high nosZ expression. To investigate whether promoter sequences affect nosZ expression, we constructed reciprocal promoter-swapped mutants between B. ottawaense and B. diazoefficiens. The swapping of promoters did not significantly affect expression levels. B. ottawaense mutants maintained approximately 200-fold higher expression levels than B. diazoefficiens, and the introduction of the B. ottawaense promoter into B. diazoefficiens did not increase expression levels. Therefore, the present results indicate that promoter sequence differences are not the primary factor affecting nosZ expression, suggesting regulation by other factors.