Nitrite and nitrous oxide reductase regulation by nitrogen oxides in Rhodobacter sphaeroides f. sp denitrificans IL106

We have cloned the nap locus encoding the periplasmic nitrate reductase in Rhodobacter sphaeroides f. sp. denitrificans IL106. A mutant with this enzy me deleted is unable to grow under denitrifying conditions. Biochemical ana lysis of this mutant shows that in contrast to the wild-type strain, the le vel of synthesis of the nitrite and N2O reductases is not increased by the addition of nitrate. Growth under denitrifying conditions and induction of N oxide reductase synthesis are both restored by the presence of a plasmid containing the genes encoding the nitrate reductase. This demonstrates that R. sphaeroides f. sp. denitrificans IL106 does not possess an efficient me mbrane-bound nitrate reductase and that nitrate is not the direct inducer f or the nitrite and N2O reductases in this species. In contrast, we show tha t nitrite induces the synthesis of the nitrate reductase.