Lithoheterotrophic growth and electron transfer chain components of the filamentous gliding bacteriumLeucothrix mucorDSM 2157 during oxidation of sulfur compounds

Evidence is presented that the type strain of filamentous gliding bacterium Leucothrix mucor DSM 2157 is capable of lithoheterotrophic growth. Thiosulfate oxidation was accompanied by accumulation of sulfate and tetrathionate in the growth medium and intracellular accumulation of elemental sulfur, as occurs in filamentous sulfur bacteria of the genus Thiothrix. Thiosulfate oxidation by L. mucor was induced during growth with a limiting concentration of organic substrate (i.e. 50–170 mg l−1 tryptone) and resulted from the induction of dissimilatory enzymes of sulfur metabolism. Metabolically useful energy was derived by both substrate-linked and oxidative phosphorylation from thiosulfate and sulfite oxidation. During sulfite oxidation the electron transfer pathway was shown to begin at the ubiquinone-cytochrome b segment of the electron transport chain. L. mucor limited by organic substrate had lowered levels of membrane bound cytochromes c and respiratory activity but a higher input of a cyanide-insensitive respiratory component than during organic enriched growth. Cytochromes aa3 and d, which had not been shown previously in this bacterium, were detected in the cells under various growth conditions. Cytochrome aa3 is suggested to take part in the electron transfer pathway from thiosulfate to oxygen which was completely inhibited by 100 µM cyanide.