Mutation of cytochrome bd quinol oxidase results in reduced stationary phase survival, iron deprivation, metal toxicity and oxidative stress in Azotobacter vinelandii

Azotobacter vinelandii cydAB mutants lacking cytochrome bd lost viability i n stationary phase, irrespective of temperature, but microaerobiosis or iro n addition to stationary phase cultures prevented viability loss. Growth on solid medium was inhibited by a diffusible factor From neighbouring cells, and by iron chelators, In(III) or Ca(III); microaerobic growth overcame in hibition by the extracellular factor. Siderophore production and total Fe(I II)-chelating activity were not markedly affected in Cyd(-) mutants, and re mained responsive to iron repression. Cyd- mutants were hypersensitive to C u(II), Zn(II), and compounds exerting oxidative stress. Failure to synthesi se haemoproteins does not explain the complex phenotype since mutants retai ned significant catalase activity. We hypothesise that Cyd(-) mutants are d efective in maintaining the near-anoxic cytoplasm required for reductive ir on metabolism and nitrogenase activity. (C) 2000 Federation of European Mic robiological Societies. Published by Elsevier Science B.V. All rights reser ved.