Xenorhabdus bharatensis sp. nov., Xenorhabdus entomophaga sp. nov., Xenorhabdus siamensis sp. nov., and Xenorhabdus thailandensis sp. nov. Isolated from Steinernema Entomopathogenic Nematodes.

Abstract

Four Gram-stain-negative bacterial strains, CS20^T, AUT15.5^T, XENO-11^T, and CCN3.3^T, isolated from Steinernema entomopathogenic nematodes, were found to represent novel species within the genus Xenorhabdus (Gammaproteobacteria, Morganellaceae). In this study, we described these new species using whole-genome phylogenomic reconstructions, sequence identity values from core genome sequences, and phenotypic characterization. Phylogenetic reconstructions based on 16S rRNA gene sequences showed that: (i) strain CS20^T is closely related to X. stockiae DSM 17904^T, (ii) strain AUT15.5^T is closely related to X. budapestensis DSM 16342^T, (iii) strain XENO-11^T is closely related to X. khoisanae DSM 25463^T, and (iv) strain CCN3.3^T is closely related to X. griffiniae DSM 17911^T. The 16S rRNA gene sequence similarity value between strain CS20^T and X. stockiae DSM 17904^T is 97.8%, between strain AUT15.5^T and X. budapestensis DSM 16342^T is 98.1%, between strain XENO-11^T and X. khoisanae DSM 25463^T is 97.8%, and between strain CCN3.3^T and X. griffiniae DSM 17911^T is 98.6%. Phylogenomic reconstructions using whole-genome sequences showed that: (i) strain CS20^T is closely related to X. stockiae DSM 17904^T and X. innexi DSM 16336^T, (ii) strain AUT15.5^T is closely related to X. indica DSM 17382^T, (iii) strain XENO-11^T is closely related to X. khoisanae DSM 25463^T, and (iv) strain CCN3.3^T is closely related to X. griffiniae DSM 17911^T. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strains CS20^T, AUT15.5^T, XENO-11^T, and CCN3.3^T and the type strains of their more closely related species are below the 70% and the 95-96% divergence thresholds, respectively, used for prokaryotic species delineation. Hence, we propose the following four new species: Xenorhabdus bharatensis sp. nov. (the type strain is CS20^T=CCM 9320^T=CCOS 2070^T), X. entomophaga sp. nov. (the type strain is XENO-11^T=CCM 9389^T=CCOS 2111^T), X. siamensis sp. nov. (the type strain is AUT15.5^T=CCM 9405^T=CCOS 2116^T), and X. thailandensis sp. nov. (the type strain is CCN3.3^T=CCM 9406^T=CCOS 2115^T). The following biochemical tests may be useful for differentiating the novel species from their more closely related taxa: acetoin production, arginine dihydrolase, citrate utilization, gelatinase, glucose oxidation, indole production, and tryptophan deaminase. Our study contributes to a better understanding of the biodiversity and phylogenetic relationships of entomopathogenic bacteria associated with insect parasitic nematodes.