Enhanced Catabolite Repression in Escherichia coli by Growth on Combined Substrates.

Catabolite repression of 3-galactosidase formation in Escherichia coli ML30 is readily observed when cultures are grown aerobically in media containing glucose or gluconate as carbon and energy sources. If cultures growing exponentially under these conditions are transferred to an anaerobic environment, catabolite repression is temporarily abolished (M. Cohn and K. Horibata, J. Bacteriol. 78:624,1959; W. J. Dobrogosz, Biochim. Biophys. Acta 100:553, 1965). The results presented in this report show that the transition from aerobiosis to anaerobiosis does not completely abolish repression if the cultures are grown in medium containing a combination of glucose and gluconate. All procedures used in these experiments were essentially identical to those described elsewhere (W. J. Dobrogosz, Biochim, Biophys. Acta 100:553, 1965). As shown in Fig. 1, cultures growing on either glu-