Xenorhabdus innovationi sp. nov., associated with the entomopathogenic nematode Steinernema innovationi from South Africa

Abstract

Summary The symbiotic bacterium, referred to as Xenorhabdus innovationi sp. nov. strain SGI-60 (synonymous to S.inno), was isolated from Steinernema innovationi SGI-60, found in grain-field soil samples from Bethlehem, South Africa. Identification was done via whole-genome phylogenomic analyses, core genome sequence identity metrics, and detailed phenotypic traits. Strain SGI-60 is Gram-negative, rod-shaped, with an average size of 1.34 × 0.38 μ m, produces lecithinase and lipase, and lacks catalase and oxidase activity. Phylogenetic reconstructions based on 16S rRNA gene sequences and whole-genome sequences showed that strain SGI-60 is closely related to X. bakwenae SF857 T , X. griffiniae Kalro, X. ehlersii DSM 16337 T , X. thailandensis CCN3.3 T and X. taiwanensis TCT-1 T . Digital DNA-DNA hybridisation (dDDH) and average nucleotide identity (ANI) values shared between strain SGI-60 and closely related species are below the prokaryotic species delineation threshold of 70 and 95%, respectively. Strain SGI-60 was identified as a member of the genus Xenorhabdus and was classified as X. innovationi sp. nov. Juveniles of S. innovationi cultured in vitro with strain SGI-60, and used to infect last-instar false codling moth larvae ( Thaumatotibia leucotreta ), killed 64% of the larvae within 48 h. This suggests that the S. innovationi–X. innovationi SGI-60 complex may be used as a biological control agent in citrus and grapevine. X. innovationi is a novel species within the genus Xenorhabdus of the family Morganellaceae, class Gammaproteobacteria. Only one isolate with these phenotypic and genotypic characteristics was isolated and strain SGI-60 is proposed as the type.