An insecticidal protein from Xenorhabdus budapestensis that results in prophenoloxidase activation in the wax moth, Galleria mellonella.

Xenorhabdus budapestensis can produce a variety of proteins that help this bacterium and its mutualistic nematode vector kill the host insect. In this report, we purified one protein fraction from the intracellular extract of X. budapestensis D43, which was designated HIP57. By injection, HIP57 caused Galleria mellonella larval bodies to blacken and die with an LD(50) of 206.81 ng/larva. Analyzes of HIP57 by two-dimensional gel electrophoresis showed that this protein was a single spot on the gel with a molecular weight of 57 kDa and a pI of ∼5. Sequencing and bioinformatic analysis suggested that the HIP57 toxin was homologous to GroEL. GroEL has been accepted as molecule chaperon; however, our research revealed that HIP57 (GroEL) possesses another novel function as an insecticide. A GroEL phylogenetic tree defined the relationship among the related species of mutualistic bacteria (Xenorhabdus and Photorhabdus) from the entomopathogenic nematodes and the evolution within the family Enterobacteriaceae. Thus, GroEL could be a complement to 16S rDNA for studying the molecular phylogenies of the family Enterobacteriaceae. Phenoloxidase (PO) activity analysis of G. mellonella larvae injected with HIP57 suggested that the toxin activates the PO cascade, which provides an extensive defense reaction that potentially responsible for G. mellonella larval death.