Reduced nicotinamide adenine dinucleotide oxidation by Thiobacillus neapolitanus and Thiobacillus strain C.

A. J. Smith, J. London, and R. Y. Stanier (J. Bacteriol. 94:972, 1967) reported that a number of obligate autotrophs, including Thiobacillus thiooxidans and T. thioparus, lacked reduced nicotinamide adenine dinucleotide (NADH2) oxidase activity, although this activity was readily detected in the facultative autotrophs T. intermedius and Hydrogenomonas eutropha. They suggested that the absence of this enzyme system provided an explanation for the inability of strict autotrophs to use organic compounds as sources of energy. Energy-linked NAD reduction, coupled to the oxidation of reduced c-type cytochromes or inorganic subsrates, has been reported by M. I.H. Aleem, H. Lees, and D. J. D. Nicholas (Nature 200:759, 1963) for the strict autotrophs Nitrobacter (nitrite-oxidizing), Nitrosomonas (hydroxylamine-oxidizing), and Ferrobacillus (ironoxidizing), and by M. I. H. Aleem (Biochem. Biophys. Acta 128:1, 1966) for T. neapolitanus, an organism which is similar in many respects to T. thioparus. There is also an extensive literature indicating that c-type cytochromes mediate electron flow from substrate to oxygen in these organisms (for example, see A. Nason, Bacteriol. Rev. 26:16, 1962; A Van Gool and H. Laudelout, Biochim. Biophys. Acta 113:41, 1966; B. A. Blaylock and A. Nason, J. Biol. Chem. 238:3453, 1963; M. I. H. Aleem and H. Lees, Can. J. Biochem. 41:763, 1963; A. B. Hooper and A. Nason, J. Biol. Chem. 240:4044, 1965; G. A. Din, I. Suzuki, and H. Lees, Can. J. Microbiol. 45:1523, 1967; P. A. Trudinger, Rev. Pure Appl. Chem. 17:1, 1967). These results suggest that a complete electron chain between NAD and oxygen should be present in some chemoautotrophs. NADH2 oxidation by extracts of T. neapolitanus was, in fact, reported by W. P. Hempfling (Ph.D. Thesis, Yale Univ., New Haven, Conn., 1963; W. P. Hempfling and W. Vishniac, Biochem. Z. 342:272, 1965): reduced nicotinamide adenine dinucleotide phosphate (NADPH)2 was oxidized at about one-third the rate of NADH2 oxidation. We have also observed NADH2 oxidation with the strict autotrophs T. neapolitanus (Thiobacillus X; C. D. Parker and J. Prisk, J. Gen. Microbiol. 8:344, 1953) and Thiobacillus strain C (D. P. Kelly and P. J. Syrett, Biochem. J. 98:537, 1966), and we have obtained evidence for coupling