Catabolite repression of extracellular amylase synthesis in Vibrio parahaemolyticus

Abstract

Some mutants of Vibrio parahaemolyticus defective in maltose utilization (Mal^-) were found to be hyperinducible for synthesis of extracellular amylase (Amy^+h). Such mutants were used conveniently to study the mechanisms of catabolite repression exerted on amylase synthesis.
Amylase synthesis in an Amy^+h Mal^- mutant, strain 3122, grown with maltotriose as the inducer, was repressed to various extents by each of 14 carbon and energy sources included in the medium. As expected, a high inverse correlation (r=-0.71) was found between thedifferential rates (DR) of enzyme synthesis and the specific growth rate constants μ observed with the individual cultures.
Cyclic adenosine 3', 5'-monophosphate (cAMP) added to the cultures generally stimulated amylase synthesis, but its extent varied greatly with the carbon and energy sources employed. The effect was demonstrated most clearly when glycerol was the carbon source, and the maximum DR obtained was about 8 times higher than that obtained without cAMP. cAMP was much less effective on stimulation of amylase synthesis when added to cultures grown on mannose, glucose, galactose, pyruvate or gluconate as the carbon and energy source. These suggest that factor (s) other than cAMP may also be involved in the enzyme repression under these conditions of cultivation.