The insecticidal-toxin repertory of 14 Xenorhabdus strains isolated from Argentina

Entomopathogenic nematodes belonging to the genus Steinernema are able to infest and kill insect hosts in association with their resident, entomopathogenic symbiont bacteria in the gram-negative genus Xenorhabdus (Enterobacteriaceae). However, only a few species of Xenorhabdus have been isolated from their hosts and their insecticidal properties reported. Here we performed the genome sequence analysis of 14 Xenorhabdus strains isolated from Steinernema nematodes in Argentina, able to kill 6th instar Galleria mellonella (Lepidoptera) larvae. The 14 draft genome sequences encoded 110 putative insecticidal toxins (Tc, Pir and Mcf toxin homologs) plus other virulence factors with similarity to putative nematicidal toxins and chitinases. The genome sequences of strains Flor, 5, PSL, Reich, 42, Vera, M, 18, Cul, DI, 12, 38, 3 and ZM exhibited 4, 9, 2, 10, 9, 5, 7, 10, 10, 7, 3, 18, 8 and 8 putative insecticidal toxin genes, respectively. Strains 5, Reich, 42, 18, DI, 38, 3 and ZM carried their predicted insecticidal toxin genes arranged into putative pathogenicity islands whereas strains Flor, PSL, Vera, M, Cul and 12) showed them spread thorough different contigs. Multigene phylogenetic analysis and average nucleotide identity (ANI) calculations were also performed and allowed the identification of three strains (PSL, Reich and 12) that should be considered as novel Xenorhabdus genomospecies. In this work, we provide a dual insight into the diversity of the species belonging to the Xenorhabdus genus and into their predicted insecticidal toxin repertory, which is currently under investigation.