A basal-defined medium for the study of proteolytic activity of Serratia marcescens

A simple defined basal medium is presented for the study of proteolytic act ivity, induction and repression, and protease purification with Serratia ma rcescens. Since the medium contains no protein, it does not interfere with or present artifact to protein assays, column chromatography, or electropho resis. The medium consists of the basal salts and buffer medium of Bromke a nd Hammel (1979) plus a carbon-energy source such as glycerol, calcium chlo ride for the cation requirement for protease activity, and an amino acid, p referably leucine. Growth parameters and proteolytic activities are present ed for unsupplemented medium and for the medium supplemented with each of 1 8 amino acids. Unsupplemented medium completes the logarithmic phase in 12. 5 h of incubation and has a constitutive level of proteolytic activity. Sup plementation with any amino acid, except cysteine and tryptophan, increases significantly the proteolytic activity, but has a varied effect on growth parameters.