B-galactosidase activity in different toxigenic and nontoxigenic strains of Vibrio cholerae: effect of glucose.

B-galactosidase activity in presence and absence of inducer lactose was examined in eight different strains of both toxigenic and nontoxigenic Vibrio cholerae (V. cholerae). In lactose (0.25 gm%) containing cultures of toxigenic strains, B-galactosidase activity was higher in stationary culture than that of logarithmic. In nontoxigenic strains, B-galactosidase activity was only 1/6th of the toxigenic strains and remained unaltered throughout growth period. While wild strains (toxigenic V. cholerae) showed B-galactosidase activity at reduced rate when grown in the medium containing both lactose and glucose, the rate of activity of B-galactosidase in nontoxigenic strains remained unchanged whether the cells were grown in lactose or lactose plus glucose. The respressive effect of higher concentration of glucose could be reversed by the addition of exogenous cyclic AMP. Low level of B-galactosidase activity in nontoxigenic strains was due to low level of intracellular cyclic AMP, compared to toxigenic strain. Furthermore, induction of enzyme activity occurred in nontoxigenic strains of V. cholerae when cyclic AMP was added exogenously.