Ammonia regulation of nod genes in Bradyrhizobium japonicum.

The expression of the nodD and nodYABC operons of Bradyrhizobium japonicum is repressed by the addition of ammonia. Repression of nodYABC expression is probably due to the effect on nodD since NodD positively regulates itself, as well as other nod operons. The effect of ammonia is independent of the known nitrogen regulatory protein, NtrC, and another regulatory protein for nitrogen fixation, NifA.