The xnp1 P2-Like Tail Synthesis Gene Cluster Encodes Xenorhabdicin and Is Required for Interspecies Competition

Xenorhabdus nematophila , the mutualistic bacterium of the nematodeSteinernema carpocapsae , produces the R-type bacteriocin called xenorhabdicin, which is thought to confer a competitive advantage for growth in the insect host. We have identified a P2-like tail synthesis gene cluster (xnp1 ) that is required for xenorhabdicin production. Thexnp1 genes were expressed constitutively during growth and were induced by mitomycin C. Deletion of either the sheath (xnpS1 ) or fiber (xnpH1 ) genes eliminated xenorhabdicin production. Production of R-type bacteriocins in a host organism had not been shown previously. We show that xenorhabdicin is produced in the hemocoel of insects infected with the wild type but not with the ΔxnpS1 deletion strain. Xenorhabdicin prepared from the wild-type strain killed the potential competitorPhotorhabdus luminescens TT01.P. luminescens was eliminated during coculture with wild-typeX. nematophila but not with the ΔxnpS1 strain. Furthermore,P. luminescens inhibited reproduction ofS. carpocapsae in insect larvae, while coinjection with wild-typeX. nematophila , but not the ΔxnpS1 , strain restored normal reproduction, demonstrating that xenorhabdicin was required for killingP. luminescens and protecting the nematode partner. Xenorhabdicin killedX. nematophila fromSteinernema anatoliense , demonstrating for the first time that it possesses intraspecies activity. In addition, activity was variable against diverse strains ofXenorhabdus andPhotorhabdus and was not correlated with phylogenetic distance. These findings are discussed in the context of the role of xenorhabdicin in the life cycle of the mutualistic bacteriumX. nematophila .