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 insertion mutations in the entomopathogenic bacterium, Xenorhabdus bovienii T228/1. Mutants which had altered expression of Congo Red binding ability, ampicillin resistance, haemolytic activity and lecithinase were isolated. Isolates with altered lecithinase activity had either lost ability to produce this enzyme or showed reduced expression. The role of lecithinase in pathogenesis of X. bovienii T228/1 for Galleria mellonella larvae was examined by LD₅₀ analysis. Maximum killing of G. mellonella was observed at 72 h post infection for both the wild-type parent strain and a lecithinase mutant 34(45). However, the LD₅₀ value for the wild-type parent strain (8·7 cells per larva) was significantly less than that calculated for the lecithinase mutant (35·5 cells per larva). The data suggested that although lecithinase is a virulence factor produced by X. bovienii , lecithinase activity alone is not sufficient for killing of G. mellonella larvae.