Respiratory Properties of Cytochrome‐c‐Deficient Mutants of Azotobacter vinelandii

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Abstract
Cytochrome‐c‐deficient mutants of Azotobacter vinelandii have been isolated following mutagenesis with N‐methyl‐N′‐nitro‐N‐nitrosoguanidine. These mutants grow well under nitrogen‐fixing conditions and studies of the physiology and energy conservation efficiency show no apparent differences from those of the parent strain. Under oxygen‐limited growth conditions, the growth rate of the cytochrome‐c‐deficient mutant was slightly slower (approx. 15%) than that of the parent strain. Cytochromes of the c‐type are required for the oxidation of artificial electron donors such as reduced N,N,N,′,N′‐tetramethyl‐p‐phenylenediamine [Ph(NMe2)2]. This study could not demonstrate a physiological role for the c‐type cytochromes which further supports the idea that the minor Ph(NMe2)2‐oxidizing pathway of the electron transport chain may be independent of the major pathway terminated by cytochrome d.