Respiratory properties of cytochrome-c-deficient mutants of Azotobacter vinelandii.

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 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.