Isolation and characterization of a Vibrio alginolyticus mutant that overproduces extracellular proteases

Abstract

The Vibrio alginolyticus prot-T1 mutant was able to produce haloes of clearing on skim milk/peptone agar plates at 42°C whereas proteolysis by the wild-type strain was inhibited at 37°C. The prot-T1 mutant overproduced the three major alkaline proteases with apparent molecular masses of approximately 28,000, 22,500 and 19,500 (proteases 1a, 2 and 3, respectively). Their synthesis was not markedly repressed by incubation at 37° C or by nonaeration. Both treatments inhibited protease synthesis in the wild-type strain, which only produced proteases during the stationary growth phase. The prot-T1 mutant synthesized proteases throughout the exponential and stationary growth phases in peptone medium. High protease activities were induced by glucose or glutamine in stationary phase prot-T1 that were pre-grown in peptide medium. Glucose or glutamine had the opposite effect on protease activities in stationary phase prot-T1 cultures that were pre-grown in minimal medium. Collagenase synthesis was not altered in the prot-T1 mutant and was repressed by growth at 37°C or without aeration. The independent control of collagenase synthesis supports the conclusion that there are no regulatory proteins responsible for the overall control of extracellular protease synthesis by temperature, aeration and growth phase in V. alginolyticus.