A comparison of the NADH oxidase electron transport systems of two obligately chemolithotrophic bacteria

Abstract

1. The NADH oxidase electron transport systems of two obligate autotrophs were investigated. Cytochromes c 547, c 550, c 552, b or c 554, b 558 and a were found in Thiobacillus neapolitanus, and cytochromes c 549, 551, c or b 555, a 1, and a or a 3 in Thiobacillus thioparus. A soluble cytochrome c 552 not present in the particulate fractions was detected in T. neopolitanus. Low potential c-type cytochromes were found in both organisms. NADH reduced both cytochromes c 547 and c 550 in the large particle fraction of T. neapolitanus, but only c 550 in the small particle fraction. 2. Both organisms contained the ubiquinone, Q-8. The levels of flavin, quinone, and cytochrome c were comparable to those of heterotrophic bacteria. No naphthoquinone was detected. 3. The levels of NADH and ascorbate oxidases were similar to those of heterotrophic bacteria, while NADH dehydrogenase and ascorbate: N, N, N′, N′-tetramethyl- p-phenylenediamine·.2HC1 (TMPD) oxidase levels were higher. In T. Thioparus, NADH oxidase activity was located exclusively in the large-particle fraction, and in T. neapolitanus in both the large- and small-particle fractions. 4. The NADH oxidase activities of both organisms were sensitive to inhibitors usually employed in studies of electron transport. NADH oxidase of T. thioparus was completely inhibited by KCN, while that of T. neapolitanus was never inhibited by more than 80%. Ascorbate and ascorbate: TMPD oxidases were sensitive to KCN but insensitive to 2-heptyl-4-hydroxyquinoline- N-moxide. 5. Electron transport pathways are proposed for both organisms.