MO-INDEPENDENT NITROGENASE 3 IS ADVANTAGEOUS FOR DIAZOTROPHIC GROWTH OF AZOTOBACTER-VINELANDII ON SOLID MEDIUM CONTAINING MOLYBDENUM

Competition experiments between wild-type Azotobacter vinelandii and a mutant lacking Mo-independent nitrogenase 3 indicate that nitrogenase 3 provides an advantage during diazotrophic growth on agar media cont aining 100 to 500 nM Na2MoO4 but not in liquid media under the same co nditions. Expression of nitrogenase 3 in wild-type cells growing on ag ar surfaces was verified with an anfH-lacZ fusion and by detection of nitrogenase 3 subunits. These results show that nitrogenase 3 is impor tant for diazotrophic growth on agar medium at molybdenum concentratio ns that are not limiting for Mo-dependent diazotrophic growth in liqui d medium.