TN5-INDUCED XENORHABDUS-BOVIENII LECITHINASE MUTANTS DEMONSTRATE REDUCED VIRULENCE FOR GALLERIA-MELLONELLA LARVAE

A derivative of Tn5 was used to construct a variety of stable insertio n mutations in the entomopathogenic bacterium, Xenorhabdus bovienii T2 28/1. Mutants which had altered expression of Congo Red binding abilit y, ampicillin resistance, haemolytic activity and lecithinase were iso lated. Isolates with altered lecithinase activity had either lost abil ity to produce this enzyme or showed reduced expression. The role of l ecithinase in pathogenesis of X. bovienii T228/1 for Galleria mellonel la larvae was examined by LD(50) analysis. Maximum killing of G. mello nella was observed at 72 h post infection for both the wild-type paren t strain and a lecithinase mutant 34(45). However, the LD(50) value fo r the wild-type parent strain (8 . 7 cells per larva) was significantl y less than that calculated for the lecithinase mutant (35 . 5 cells p er larva). The data suggested that although lecithinase is a virulence factor produced by X. bovienii, lecithinase activity alone is not suf ficient for killing of G. mellonella larvae.