Catabolite repression of tryptophanase was studied in detail under various conditions in several strains of Escherichia coli and was compared with catabolite repression of f,-glactosidase. Induction of tryptophanase and ,B-galactosidase in cultures grown with various carbon sources including succinate, glycerol, pyruvate, glucose, gluconate, and arabinose is affected differently by the various carbon sources. The extent of induction does not seem to be related to the growth rate of the culture permitted by the carbon source during the course of the experiment. In cultures grown with glycerol as carbon source, preinduced for ,B-galactosidase or tryptophanase and made permeable by ethylenediaminetetraacetic acid (EDTA) treatment, catabolite repression of tryptophanase was not affected markedly by the addition of cAMP (3', 5'-cyclic adenosine monophosphate). Catabolite repression by glucose was only partially relieved by the addition of cAMP. In contrast, under the same conditions, cAMP completely relieved catabolite repression of ,@-galactosidase by either pyruvate or glucose. Under conditions of limited oxygen, induction of tryptophanase is sensitive to catabolite repression; under the same conditions, ,B-galactosidase induction is not sensitive to catabolite repression. Induction of tryptophanase in cells grown with succinate as carbon source is sensitive to catabolite repression by glycerol and pyruvate as well as by glucose. Studies with a glycerol kinaseless mutant indicate that glycerol must be metabolized before it can cause catabolite repression. The EDTA treatment used to make the cells permeable to cAMP was found to affect subsequent growth and induction of either ,B-galactosidase or tryptophanase much more adversely in E. coli strain BB than in E. coli strain K-12. Inducation of tryptophanase was reduced by the EDTA treatment significantly more than induction of ,B-galactosidase in both strains. Addition of 2.5 x 10-3 M cAMP appeared partially to reverse the inhibitory effect of the EDTA treatment on enzyme induction but did not restore normal growth. MATERIALS AND METHODS Bacterial strains. Escherichia coli mi 14 was isolated from the feces of a conventionally raised laboratory mouse and was identified on the basis of Gram stain, motility, IMViC reactions, and growth characteristics.
The distribution of tryptophanase wa's studied. The highest observed specific activity, ,moles per minute per milligram (dry weight) cells, is given in parentheses after each species. Tryptophanase was inducible and repressible in Escherichia coli (.914), Paracolobactrum coliforme (.210), Proteus vulgaris (.146), Aeromonas liquefaciens (.030), Photobacterium harveyi (.035), Sphaerophorus varius (.021), Bacteroides sp. (.048), and Corynebacterium acnes (.042). The enzyme was constitutive and nonrepressible in Bacillus alvei (.013), and was inducible but not repressible by glucose in Micrococcus aerogenes (.036). Indole-positive bacteria were found in fecal or intestinal samples from a variety of animals among the mammals, reptiles, insects, molluscs, fish, crustaceans, and amphibians.
The mechanism of ethanol production in bacterial fermentations has not been elucidated. Among the alcohol-producing bacterial systems available for study, the mixed ethanol-lactate fermentation characteristic of the heterofermentative lactic acid bacteria presents an interesting and apparently relatively simple case for experimentation. The major products of glucose fermentation by these organisms are lactic acid, ethanol, and carbon dioxide. Gayon and Dubourg (1901), Peterson and Fred (1920), and Nelson and Werkman (1935) have shown the occurrence of two fermentation patterns among the heterofermentative lactobacilli. With glucose as substrate, these are: (1) the production of lactate, ethanol, and C02, with occasional traces of acetate and (2) the formation of glycerol along with lactate, acetate, and C02. Among the heterofermentative cocci, genus Leuconostoc, Pederson (1929) found only the first type-glucose fermentation yielded equimolar quantities of lactate, ethanol, and C02. Friedemann (1939) confirmed this fermentation balance using Leuconostoc dextranicum as did Bang (1945) for Leuconostoc citrovorus. With one nucleotide-linked dehydrogenases for ethanol, lactate, triosephosphate, and 2,3butylene glycol. The lactic dehydrogenase is specific for D(-)lactic acid, the
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