Xanthomonas campestris NCIB 11854 was grown glucose-limited in continuous culture at 28 °C, pH 6·8, in a defined minimal salts medium. Whole cells contained cytochromes b, c, aa3, o-type cytochromes and possibly a1, and yielded →H+/O quotients of up to approximately 6 for the oxidation of endogenous substrates. These data, by analogy with results obtained previously with other species of bacteria, suggest the presence of up to three sites of respiratory chain energy conservation. However, molar growth yields on glucose [Ymaxglucose = 53·6 g dry wt bacteria (mol glucose)−1] and oxygen [YmaxO2 = 26·4 g dry wt bacteria (mol O2)−1] were extremely low and indicated an ATP/O quotient of approximately 1 which was only marginally increased when corrected for polymer production. A relatively rapid decay of the pH gradient generated by in vitro respiration was observed, probably indicating either an enhanced permeability of the cytoplasmic membrane to H+ or a rapid rate of ATP turnover, either of which could in part account for the observed low growth efficiency of the organisms.
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