Growth and proton-potassium exchange in the bacterium Enterococcus hirae: the effect of protonophore and the role of redox potential

Abstract

The bacterium Enterococcus hirae is able to grow under anaerobic conditions during sugar fermentation (pH 8.0) in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone at a considerably lower specific rate. Bacterial growth was accompanied by acidification of the medium and a drop in its redox potential from positive to negative values (by −220 mV). We showed that the reducer dithiothreitol, which determines negative values of the redox potential, accelerates bacterial growth and enhances acidification of the medium, abolishing the effect of the protonophore without binding to dithiothreitol. Conversely, the nonpenetrating oxidant ferricyanide, which maintained positive values of the redox potential, suppressed bacterial growth. These results are indicative of the role of the proton-motive force and the importance of reductive processes in bacterial growth. The proton-potassium exchange is inhibited in the presence of carbonyl cyanide m-chlorophenylhydrazone and recovers in the presence of dithiothreitol. Dithiothreitol can substitute for the proton-motive force; however, both ferricyanide and dithiothreitol may have a direct effect on the bacterial membrane.