R. Dmello et al., EXPRESSION AND CONTENT OF TERMINAL OXIDASES IN AZOTOBACTER-VINELANDIIGROWN WITH EXCESS NH4-2 SUPPLY( ARE MODULATED BY O), Microbiology, 143, 1997, pp. 231-237
The influence of the rate of O-2 supply to batch cultures on the conte
nts of cytochromes bd and 'o' in NH4+-grown Azotobacter vinelandii has
been investigated, Difference spectra at room temperature (reduced CO minus reduced) were recorded for whole cells of a wild-type strain
and mutants which either lacked or over-produced the cytochrome bd-typ
e terminal oxidase encoded by cydAB, A Tn5-B20 insertion in cydB in th
e former mutant also provided a means of monitoring cydAB gene express
ion from measurements of beta-galactosidase activity. The content of c
ytochrome d in the wild-type, and the expression of cydAB-lacZ, in the
mutant, increased as the O-2 supply was raised, suggesting that O-2 r
egulates cydAB expression even in the absence of diazotrophy. In a str
ain carrying a mutation in cydR, a regulatory gene upstream of cydAB,
and which over-produces cytochrome bd. the responses to O-2 supply dur
ing growth at different O-2 supply rates were reversed. Changes in the
content of a haemoprotein detectable in low temperature photodissocia
tion spectra, and attributed to cytochrome b(595) - the high-spin cyto
chrome b component of the cytochrome bd complex - followed the changes
in cytochrome d levels. CO difference spectra of both the wild-type s
train and the cytochrome bd-deficient mutant revealed a haemoprotein w
ith spectral characteristics similar to cytochrome o, the levels of wh
ich increased as the O-2 supply was raised. These results are discusse
d with reference to previous reports of cytochrome changes in cells gr
own under N-2-fixing conditions.