Oxidation of endogenous substrates and ferrous iron in a chemoautotrophic bacterium Acidithiobacillus (Thiobacillus) ferrooxidans

Effects of uncouplers and electron transport inhibitors have been studied on the oxygen-coupled oxidation of Fe2+, endogenous substrates and formic acid by Acidithiobacillus ferrooxidans. Fe 2+ oxidation was slightly stimulated by low concentrations of uncouplers within one minute indicating a normal respiratory control during Fe 2+ oxidation, although higher concentrations of uncouplers were inhibitory. Complex I inhibitors rotenone, amytal and atabrine, and complex III inhibitors antimycin A, myxothiazol and 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), partially inhibited Fe2+ oxidation and the reduced activities by these inhibitors were stimulated by an uncoupler 2,4-dinitrophenol or carbonyl cyanide m-chlorophenylhydrazone with the exception of atabrine-reduced activity. These results support the interpretation that some electrons were flowing along the uphill (endergonic) electron transport pathway to reduce NAD + during Fe2+ oxidation. Complex I inhibitor piericidin A showed no effect on Fe2+ oxidation and the reduced activity of Fe2+ oxidation by atabrine could be further inhibited by the addition of an uncoupler. Some organic compounds such as ascorbic acid, propyl gallate (PG), salicylhydroxamic acid (SHAM), L-cysteine, glutathione and tiron can be oxidized by A. ferrooxidans using the Fe 2+-oxidizing system. These compounds could chemically reduce Fe 3+ to Fe2+ and their oxidation by the cells was greatly stimulated by the addition of FeCl3. Their oxidation was also not sensitive to the inhibition by piericidin A but was inhibited by atabrine and the reduced activities by atabrine can also be further inhibited by an uncoupler. Other inhibitors and uncouplers showed qualitatively similar but quantitatively different effects on the oxidation of these organic compounds compared to those on Fe2+ oxidation.; The oxidation of endogenous substrates in A. ferrooxidans by O2 or Fe3+ (endogenous oxidation) was greatly stimulated by uncouplers, ionophores and weak acids, indicating a normal respiratory control during endogenous oxidation. Complex I inhibitors, rotenone, amytal and piericidin A, strongly inhibited endogenous oxidation indicating a downhill (exergonic) electron transport pathway for this oxidation. Atabrine did not inhibit endogenous oxidation but inhibited Fe2+ oxidation while piericidin A inhibited endogenous oxidation but did not inhibit Fe 2+ oxidation, suggesting the possibility of two types of complex I (NDH-1) in A. ferrooxidans: one (NDH-1down) involved in the downhill reaction (NADH oxidation) and the other (NDH-1up) involved in the uphill reaction (NAD+ reduction). (Abstract shortened by UMI.)...