Characterization of a spontaneous mutant of Azotobacter vinelandii in which vanadium-dependent nitrogen fixation is not inhibited by molybdenum
1998
Bageshwar, U.K. | Raina, R. | Das, H.K.
A spontaneous mutant derivative of Azotobacter vinelandii CA12 (delta nifHDK), in which vanadium-dependent nitrogen fixation is not inhibited by molybdenum (A. vinelandii CARR), grows profusely on BNF-agar containing 1 micromolar Na2MoO4, alone or supplemented with 1 micromolar V2O5. The expression of A. vinelandii vnfH::lacZ and vnfA::lacZ fusions in A. vinelandii CARR was not inhibited by 1 mM Na2MoO4, whereas molybdenum at much lower concentration inhibited the expression of vnfH::lacZ and vnfA::lacZ fusions in A. vinelandii CA12. The mutant also exhibited normal acetylene reduction activity in the presence of 1 micromolar Na2MoO4. The expression of A. vinelandii nifH::lacZ fusion in A. vinelandii CARR was low even though the cells were cultured under non-repressing conditions with urea as nitrogen source in the presence of Na2MoO4. The molybdenum content of A. vinelandii CARR cells was found to be about one-fourth that of A. vinelandii CA12. No nitrate reductase activity could be detected in A. vitlandii CARR when the cells were cultured in the presence of 10 micromolar Na2MoO4, whereas A. vinelandii CA12 exhibited some activity even with 100 pM Na2MoO4.
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