Respiratory chain of the alkalophilic bacterium Bacillus firmus RAB and its non-alkalophilic mutant derivative

Abstract

The membrane-bound respiratory chain components of alkalophiic Bacillus firmus RAB were studied by difference spectroscopy and oxidation-reduction potentiometric titrations. Cytochromes with the following midpoint potentials were identified at pH 9.0: a-type cytochromes, +110 and +210 mV; b-type cytochromes, +20,-120,-280, and-400 mV; and cytochrome c, +60 mV. Only the higher-potential cytochrome a showed an upward shift in midpoint potential when titrated at pH 7.0. Parallel studies of a non-alkalophilic mutant derivative of B. firmus RAB, strain RABN, revealed the presence of only one species each of a-, band nd c-type cytochromes which exhibited midpoint potentials of +110,-150, and +160 mV, respectively, at pH 7.0. Membranes of both strains were found to contain menaquinone. At pH 9.0, NADH caused the reduction of essentially all of the cytochromes that were seen in fully reduced preparations of wild-type B. firmus RAB membranes. By contrast, at pH 7.0, NADH failed to appreciably reduce the b-type cytochromes. These findings may relate to our recent proposal that an inadequacy in energy transduction (production of a proton motive force) by the alkalophilic respiratory chain at pH 7.0 is what precludes the growth of B. firmus RAB at a neutral pH.

Electrical Stress-Directed Evolution of Biocatalyst Texcoco Soil Community for Microbial Fuel Cell

“…This value was draw closer to the alkaliphilic cytochromes potential range (11). It could be the Soluble/membrane-bound cytochromes from alkaliphilic bacteria are characterized (9,(11)(12)(13), a feature which could facilitate electron transfer to the membrane-bound terminal oxidase in the presence of the large negative membrane potentials was associated with the alkaline pH growth medium (8). One of the possible ECS Transactions, 36 (1) 3-11 (2011) reasons for the irreversible process would be the electrode surface that apparently fouled by strong irreversible adsorption (14), due to long term growth of bio films.…”

Purification and characterization of the cytochrome oxidase from alkalophilic Bacillus firmus RAB

“…It is thus notable that these organisms are found to have very high concentrations of membrane-associated respiratory chain components (17) and that the array of cytochromes, as distinguished by redox potentials, is complex. In both Bacillus alcalophilus (19) and Bacillus firmus RAB (14), a c-type cytochrome, numerous cytochrome b species, and a terminal oxidase of the cytochrome aa3 type have been detected. Although one of the minor b-type cytochromes might be a cytochrome o (14), cytochrome aa3 is the major terminal oxidase of the two alkalophiles and is apparently the sole terminal oxidase of non-alkalophilic mutant derivatives.…”

“…In both Bacillus alcalophilus (19) and Bacillus firmus RAB (14), a c-type cytochrome, numerous cytochrome b species, and a terminal oxidase of the cytochrome aa3 type have been detected. Although one of the minor b-type cytochromes might be a cytochrome o (14), cytochrome aa3 is the major terminal oxidase of the two alkalophiles and is apparently the sole terminal oxidase of non-alkalophilic mutant derivatives. We have speculated that the abundance and complexity of the alkalophilic respiratory chain may confer upon the organism the requisite capacity to pump protons with optimal efficacy and thus meet the cellular energy requirements (15,19).…”