The cytochrome composition of carboxydotrophic bacteria

Abstract

Spectroscopy at room and liquid nitrogen temperatures with extracts of the carbon monoxide-oxidizing bacteria Pseudomonas carboxydovorans, P. carboxydohydrogena, P. carboxydoflava, P. compransoris, Alcaligenes carboxydus, and Arthrobacter 11/x revealed the presence of normal electron transport systems, containing b-, c-, and a-type cytochromes at concentrations that compare to those of other aerobic bacteria. CO did not induce the formation of special CO-insensitive terminal oxidases. The gross composition of the respiratory chains was not affected by the type of growth substrate, and cytochrome d(=a2) was not detected. However, certain b-type cytochromes were only found when CO or H2 + CO2 served as growth substrates. All strains contained at least two different b-type cytochromes. Cytochrome b563 formed a weak CO-complex and was identified as a novel cytochrome o. It functions as CO-insensitive, alternative terminal oxidase in carboxydotrophic bacteria. A soluble CO-binding cytochrome c was present in P. carboxydovorans, P. carboxydohydrogena, and P. carboxydoflava. A CO-binding protoheme compound could be identified as catalase in P. compransoris, P. carboxydovorans, P. carboxydohydrogena, A. carboxydus, and Arthrobacter 11/x. The data are consistent with the presence of branched respiratory chains in the carboxydotrophs examined, and suggest the functioning of both, cytochrome a and the novel cytochrome o as terminal oxidases.