Anaerobic Respiration and Energy Conservation in<i>Paracoccus denitrficans</i>

Abstract

Electron paramagnetic resonance spectra at 8–60 K of NADH‐reduced membrane particles prepared from Paracoccus denitrificans grown anaerobically with nitrate as terminal electron acceptor show the presence of iron‐sulfur centers 1–4 in the NADH‐ubiquinone segment of the respiratory chain. In addition resonance lines at g = 2.058, g = 1.953 and g = 1.88 are detectable in the spectra of succinate‐reduced membranes at 15 K, which are attributed to the iron‐sulfur‐containing nitrate reductase. Sulphate‐limited growth under anaerobic conditions does not affect the iron‐sulfur pattern of NADH dehydrogenase or nitrate reductase. Furthermore respiratory chain‐linked electron transport and its inhibition by rotenone are not influenced. These results contrast those observed for sulphate‐limited growth of P. denitrificans under aerobic conditions [ Eur. J. Biochem. (1977) 81 , 267–275]. Proton translocation studies of whole cells indicate that nitrite increases the proton conductance of the cytoplasmic membrane, resulting in a collapse of the proton gradient across the membrane. Nitrite accumulates under anaerobic growth conditions with nitrate as terminal electron acceptor; the extent of accumulation depends on the specific growth conditions. Thus the low efficiencies of respiratory chain‐linked energy conservation observed during nitrate respiration [ Arch. Microbiol. (1977) 112 , 17–23] can be explained by the uncoupling action of nitrite.