Energy transduction in the mitochondrionlike bacterium Paracoccus denitrificans during carbon- or sulphate-limited aerobic growth in continuous culture

Abstract

P. denitrificans was grown in C-limited aerobic continuous culture (critical dilution rate (Dc) = 0.48 h-1). The molar growth yield for C (succinate or malate) was constant at about 60 over a broad dilutin range (growth range) from 0.10-0.48 h-1. Measurements of the stoichiometry of proton translocation associated with the oxidation of endogenous substrates yielded a ratio of protons ejected from the cell per atom of oxygen consumed (.fwdarw. H+:O) of 8.55 which decreased to 5.85 in the presence of piericidin A (PA), a specific inhibitor of NADH dehydrogenase (EC 1.6.99.3). With starved cells, the observed .fwdarw. H+:O associated with the oxidation of added succinate in the presence of PA was 5.61. These observed .fwdarw. H+:O represent an underestimation since no correction was made for proton backflow during the short interval of respiratory activity. Aerobic growth of P. denitrificans in the chemostat becomes sulfate limited at entering concentrations of sulphate < 300 .mu.M. Neither the maximum specific growth rate (measured at Dc) nor the observed molar growth yield for succinate decreased under sulfate limitation. The NADH oxidase in electron transport particles prepared from sulfate-limited cells was completely inhibited by PA. The stoichiometry of proton translocation associated with malate oxidation was similarly unaffected by sulfate limitation. Apparently, the respiratory chain of aerobic, heterotrophically grown P. denitrificans possesses 3 sites of energy conservation, including site III, the number of protons ejected during the transfer of 1 pair of reducing equivalents along a region of the electron transport chain equivalent to a single energy-coupling site is 3, and sulfate limitation does not lead to a loss of proton translocation associated with the cytochrome-independent region of the respiratory chain.