Direct correlationship between proton translocation and growth yield: An analysis of the respiratory chain of Bacillus stearothermophilus

Abstract

Thermophilic bacilli contain cytochrome caa 3-type cytochrome c oxidase as the main terminal oxidase in the respiratory chain. A mutant strain, named K-17, lacking cytochrome caa 3 and exhibiting very low N,N,N′,N′-tetramethyl- p-phenylene diamine oxidase activity, was isolated by random mutation from Bacillus stearothermophilus K1041 (Sakamoto, J. et al., FEMS Microbiol. Lett., 143, 151–158, 1996). Comparing this mutant with the parent strain K1041, we obserbed the following differences in energy-yielding properties. (i) K-17 gave an cell yield less than one half of that of the wild type, although the doubling time of K-17 was only a little slower than that of the parent strain. (ii) In cellular respiration, the H +/O ratio of K-17 was 2.9–3.1, while that of the wild type was 6.1–6.5. (iii) A low concentration of cyanide inhibited endogenous respiration of the wild-type cells partly with a concomitant reduction of the H +/O ratio to around 3, while it did not significantly affect the respiration rate and the H +/O ratio of the K-17 cells. (iv) Cytochrome bd-type quinol oxidase seemed to operate in the wild-type cells when a low concentration (below 0.5 mM) of cyanide was added, while this enzyme is the main terminal oxidase in K-17. The K-17 cells also contained cytochrome b(o/a) 3-type cytochrome c-551 oxidase. These results demonstrated that the combination of the enzymes involved in the respiratory chain determines the H +/O ratios of the cell and consequently the growth yield of the bacteria.