Exocellular proteases ofSerratia marcescens and their toxicity to larvae ofGalleria mellonella

Abstract

Out of 18 strains ofSerratia marcescens producing exocellular proteases the strainSerratia 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 enzymes could be demonstrated by means of specific inhibitors EDTA and diisopropyfluorophosphate: metaloprotease 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 50 ° 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 ofGalleria mellonella.