Exocellular proteases of Serratia marcescens and their toxicity to larvae of Galleria mellonella.

Out of 18 strains of Serratia marcescens producing exocellular proteases the strain Serratia marcescens CCEB 415 was selected according to preliminary experiments. It could be shown that the train exhibits proteolytic activity reaching up to 10 TU per 1 ml of the culture filtrate in a medium with gelatine and peptone. Two proteolytic enzyme could be demonstrated by means of specific inhibitors EDTA and diisopropyfluorophosphate: metalprotease with optimum activity at pH 7.5 and serine protease with pH optimum of 10.9. The enzymes were purified on Sephadex and DEAE cellulose columns and by means of gel electrophoresis. However, it was not possible to separate them. The optimum temperature for activity of the mixture of the two enzymes was 50degrees C, molecular weight varied around 37000 (according to gel filtration); certain kinetic characteristics of their activity were determined. Excess subtrate (casein) inhibited activity of the enzyme mixture. Toxicity of proteases expressed as LD50 units equals 78 - 10(3) TU per larva of Galleria mellonella.