Studies on the activation of the prophenoloxidase system of insects by bacterial cell wall components

Abstract

The ability of bacterial cell walls to activate the prophenoloxidase cascade was tested using Blaberus craniifer, Clitumnus extradentatus, Locusta migratoria and Schistocerca gregaria. Effects of modifying components of the cell wall on the activation of prophenoloxidase in a haemocyte lysate supernatant preparation were examined. Peptidoglycan was found to be an important factor for the activating ability of Gram-positive bacteria. Lysozyme treatment of Micrococcus luteus cell wall showed that the soluble peptidoglycan was the active component. Teichoic acid isolated from Staphylococcus aureus did not activate the prophenoloxidase cascade. However, removal of teichoic acid from the cell wall enhanced activation, probably by exposure of peptidoglycan. Several Escherichia coli K-12 strains, with differing lipopolysaccharide compositions, were also tested for activation of prophenoloxidase. Differences in the ability of the various strains to activate the prophenoloxidase cascade were apparent although no clear conclusions could be made. The role of capsular polysaccharides was investigated too, using two Klebsiella pneumoniae strains, a noncapsulate mutant and its capsulate parent strain. The capsular polysaccharide conferred an increased activating potential. This difference in activation was lost by removal of the capsule from the parent strain. These results are interpreted in terms of the nonself recognition process in insect haemolymph.