RT Journal Article SR Electronic(1) A1 Flyg, Casper A1 Xanthopoulos, Kleanthis G.YR 1983 T1 Insect Pathogenic Properties Of Serratia Marcescens. Passive And Active Resistance To Insect Immunity Studied With Protease-deficient And Phage-Resistant Mutants JF Microbiology, VO 129 IS 2 SP 453 OP 464 DO https://doi.org/10.1099/00221287-129-2-453 PB Microbiology Society, SN 1465-2080, AB Many insects have a cell-free immune system in which small basic proteins called cecropins are the main defence against Gram-negative bacteria. We have earlier shown that an insect pathogenic strain of Serratia marcescens was resistant to insect immunity and that certain mutants resistant to phage ɸJ become sensitive to cecropins. We have found that protease-deficient mutants with and without resistance to ɸJ appear to be deficient in the mechanism of protease induction. Three different protease fractions exist and for two of the enzymes we describe a partial purification and characterization. The proteases show pronounced autodegradation which increases with the purity. Both enzymes are only partly affected by EDTA and they are highly toxic to Drosophila melanogaster. All three enzymes destroy cecropins in immune haemolymph from Cecropia pupae. However, in vivo experiments with different mutants indicate that in Serratia, passive resistance to insect immunity is more important for virulence in Drosophila than the production of proteases which can destroy cecropins., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-129-2-453