โ Scribed by Groot, G. N. ;Stouthamer, A. H.
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Proteus mirabilis can form four reductases after anaerobic growth: nitrate reductase A, chlorate reduetase C, thiosulfate reductase and tetrathionate reductase. The last three enzymes are formed constitutively. Nitrate reductase is formed only after growth in the presence of nitrate, which causes repression of the formation of thiosulfate rednctase, chlorate reduetase C, tetrathionate reductase and hydrogenase. Formic dehydrogenase assayed with methylene blue as hydrogen accepter is formed under all conditions.
Two groups of chlorate resistant mutants were obtained. One group does not form the reductases and formic dehydrogenase. The second group does not form nitrate reductase, chlorate reductase and hydrogenase, but forms formic dehydrogenase and small amounts of formic hydrogenlyase after growth without hydrogen accepter or after growth in the presence of thiosulfate or tctrathionate. Nitrate prevents the formation of formic dehydrogenase, thiosulfate reductase and tetrathionate reductase in this group of mutants. Only after growth with thiosulfate or tetrathionate the reductases for these compounds are formed. Anaerobic growth of the wild type in complex medium without a fermentable carbon source is strongly stimulated by the presence of nitrate. Tetrathionate and thiosulfate have no effect at all or only a small effect. The results show that in the presence of tetrathionate or thiosnlfate the bacterial metabolism is fully anaerobic, as these cells also contain formic hydrogenlyase. ~qitrate reductaseless mutants of Enterobacteriaceae have recently been isolated in several laboratories. They were obtained by selection for resistance against chlorate, which is reduced to toxic products by nitrate reduetase. These mutations have been found to be pleiotropic. They cause the loss of nitrate reductase and formic hydrogenlyase in both Aerobacter aerogenes (STouT~AM]~I~, 1967a, b) and in Escherichia cell (I:)I]~CtIAUD et al., 1967). It has been shown that these mutants lack formic dehydrogenase of the formic hydrogenlyase complex (STovT~A~E~ et al., 1967;O'HARA et al., 1967; VISUAliZES et al., 1968). Similar mutants of Proteus vulgaris ]ack nitrate reductase, formic hydrogenlyase, thiosulfate reduetase and tetrathionate reduetase
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