Abstract

Three bacterial strains, XENO-2(T), XENO-7(T), and XENO-10(T), isolated from Steinernema entomopathogenic nematodes, were found to represent novel Xenorhabdus species. In this study, we describe these new species by whole-genome and whole-proteome phylogenomic reconstructions, by calculating sequence identity scores using core genome sequences, and by phenotypic characterization. Phylogenomic reconstructions using ribosomal and house-keeping genes, and whole-genome and whole-proteome sequences show that XENO-2(T) and XENO-10(T) are closely related to Xenorhabdus japonica DSM 16522(T) and that XENO-7(T) is closely related to Xenorhabdus bovienii subsp. africana XENO-1(T) and to X. bovienii subsp. bovienii T228(T). The dDDH values between XENO-2(T) and XENO-10(T) and between XENO-2(T) and X. japonica DSM 16522(T) are 56.4 and 51.8%, respectively. The dDDH value between XENO-10(T) and X. japonica DSM 16522(T) is 53.4%. The dDDH values between XENO-7(T) and X. bovienii subsp. africana XENO-1(T) and between XENO-7(T) and X. bovienii subsp. bovienii T228(T) are 63.6 and 69.4%, respectively. These dDDH values are below the 70% divergence threshold for prokaryotic species delineation. The newly described species are highly pathogenic to G. mellonella larvae, grow at pH between 5 and 9 (optimum 5-7), at salt concentrations of 1-3% (optimum 1-2%), and temperatures between 20 and 37 degrees C (optimum 28-30 degrees C). Biochemical tests such as lysine decarboxylase, ornithine decarboxylase, urease, gelatinase, citrate utilization, indole and acetoin production, and cytochrome oxidase tests allow to differentiate the novel species from their more closely related species. Considering these genetic and phenotypic divergencies, we propose the following new species: Xenorhabdus aichiensis sp. nov. with XENO-7(T) (= CCM 9233(T) = CCOS 2024(T)) as the type strain, Xenorhabdus anantnagensis sp. nov., with XENO-2(T) (= CCM 9237(T) = CCOS 2023(T)) as the type strain, and Xenorhabdus yunnanensis sp. nov., with XENO-10(T) (= CCM 9322(T) = CCOS 2071(T)) as the type strain. Our study contributes to a better understanding of the biodiversity and phylogenetic relationships of entomopathogenic bacteria associated with insect parasitic nematodes.