Respiratory physiology and energy conservation efficiency of Campylobacter jejuni

Abstract

A study of the electron transport chain of the human intestinal pathogen Campylobacter jejuni revealed a rich complement of b- and c-type cytochromes. Two c-type cytochromes were partially purified: one, possibly an oxidase, bound carbon monoxide whereas the other, of high potential was unreactive with carbon monoxide. Respiratory activities determined with membrane vesicles were 50- to 100-fold higher with formate and hydrogen than with succinate, lactate, malate, or NADH as substrates. Evidence for three terminal respiratory components was obtained from respiratory kinetic studies employing cyanide, and the following Ki values for cyanide were determined from Dixon plots: ascorbate + reduced N,N,N', N'-tetramethyl-p-phenylenediamine, K1 + 3.5 muM; malate, K1 = 55 muM; and hydrogen, K1 = 4.5 muM. Two oxidases (K1 = 90 muM, 4.5 mM) participated in the oxidation of succinate, lactate, and formate. Except with formate, 37 muM HQNO inhibited respiration by approximately 50%. Carbon monoxide had little inhibitory effect on respiration except under low oxygen tension (less than 10% air saturation). The stoichiometry of respiratory-driven proton translocation (H+/O) determined with whole cells was approximately 2 for all substrates examined except hydrogen (H+/) = 3.7) and formate (H+/O = 2.5). The higher stoichiometries observed with hydrogen and formate are consistent with their respective dehydrogenase being located on the periplasmic face of the cytoplasmic membrane. The results of this study suggest that the oxidation of hydrogen and formate probably serves as the major sources of energy for growth.