Protease and lipase production by a strain ofSerratia marcescens (532 S)

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Abstract
Production of both exolipase and exoprotease activities bySerratia marcescens 532 S isolated from an aerobic fixed-biomass reactor were strongly influenced by nutritional factors which acted as inducers or repressors. In batch culture, protease and lipase activities were produced after the exponential phase. NH4Cl, amino acids and simple carbon sources caused repression of protease activity. At a concentration of 1.5 g L−1, the individual addition of maltose, mannitol, acetate, fructose or glucose, repressed exoprotease production, with the greatest effect by glucose. An inverse relationship existed between exoprotease synthesis and increasing glucose concentrations. Lipids activated lipase production, the most significant increase occurred when Tween 80 was added in the medium. Thus, glucidolytic, proteolytic and lipolytic activities could be efficiently expressed in batch cultures only successively. At low dilution rate of chemostat cultures with a constant glucose input concentration of 2 g L−1, glucidolytic, proteolytic and lipolytic activities were produced, but did not have the same regulation: atD values −1, the level of protease activity dropped while that of lipase showed a corresponding increase. Above these values, increasingD led to a decrease of the two hydrolase activities, at the level of the specific activities as well as in the specific rate of biosynthesis of each enzyme. Similar results were obtained in chemostat culture with a constant specific growth rate of 0.04 h−1 with increasing glucose input concentrations, i.e. protease and lipase activities decreased when the specific glucose uptake rates were enhanced.