Respiratory mutants of Azotobacter vinelandii with elevated levels of cytochrome d

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Abstract
A method is described for the isolation of respiratory mutants of Azotobacter vinelandii with increased amounts of d-type cytochrome by selecting for the inability to reduce tetrazolium red. Five stable mutants were obtained that had six-fold higher levels of cytochrome d, increased amounts of b-type and lower amounts of o-type and c-type cytochromes than the wild-type strain. Spectral alterations in cytochrome a1 were also observed in the mutants. NADH and succinate oxidase activities of membrane particles were about two fold higher in the mutants compared to the wild-type strain. Ascorbate-N,N,N′,N′-tetramethyl-p-phenylene diamine oxidase activity was barely detectable in membrane particles of the mutants. These results are consistent with an increase in the amount of the cytochrome d oxidase branch and a decrease in the amount and activity of the cytochrome o, a1 oxidase branch in the mutants. Growth rates under oxygen-excess conditions and respiratory-linked proton translocation ratios of the mutant and wild-type strains were similar as were the photochemical spectral and kinetic properties of cytochrome d.