Influence of organic acids on the growth ofThiobacillus neapolitanus

An ether-soluble fraction of yeast extract was found to bring about the reduction of cytochromes of thec type in crude cell-free extracts of autotrophically grown cells ofT. neapolitanus. Re-extraction of the ether-soluble fraction with petroleum ether resulted in marked decrease in its ability to reduce the cytochromes ofT. neapolitanus. Among several organic acids tested only succinate was effective in reducing the cytochromes. Acetate at 20mm concentration was a potent inhibitor of growth, although thiosulfate oxidation by intact cells was only slightly affected. No poly-β-hydroxybutyric acid was found in cells grown on thiosulfate in the presence or absence of non-inhibitory concentrations of acetate. Glycollic acid was not inhibitory to growth at concentrations up to 60mm. Glycollic oxidase could not be demonstrated in crude extracts, however glyoxylic reductase was present in high concentrations. In cells fixing¹⁴CO₂ in the presence or α-hydroxypyridyl-methanosulfonic acid, (HPMSA), a specific inhibitor of glycollic acid oxidase, 18% of the total radioactivity extracted by 95% alcohol was present in glutamate, whereas in the absence of HPMSA, glutamate accounted only for about 9% of the total radioactivity. No accumulation of glycollic acid, glycine or serine was observed in the presence of HPMSA. It appears that glycollic acid formation does not participate to a significant extent in CO₂ fixation by this organism. α-Hydroxypyridylmethanosulfonic acid appears to act differently on this obligate autotroph than on photosynthetic organisms.