Expression from symbiotic promoters of Rhizobium meliloti in Azotobacter vinelandii and Azospirillum brasilense.

In Rhizobium meliloti, the promoter P1 of the nif HDK operon, and also the promoter P2, have earlier been shown to be active in the bacteria present in alfalfa root nodules, but not in the bacteria grown aerobically in culture. Here we have looked at the expression from P1 and P2 in two non-symbiotic nitrogen-fixing bacteria, Azotobacter vinelandii and Azospirillum brasilense, using constructions in which the promoters are fused upstream of the ß-galactosidase gene. The promoter P1, but not P2, is active in A. vinelandii, while neither P1 nor P2 is active in Azospirillum brasilense.