Abstract
Two slightly yellowish-pigmented, oxidase-negative, rod-shaped and Gram-stain-negative bacterial strains (30TX1(T) and DL20(T)), isolated from Steinernema sangi and Steinernema eapokense, respectively, during soil sampling in Vietnam were studied using a polyphasic taxonomic approach. Strain 30TX1(T) showed highest 16S rRNA gene sequence similarity to the type strain of Xenorhabdus ehlersii (98.9 %) and strain DL20(T) to that of Xenorhabdus ishibashii (98.7 %). Sequence similarities to all other Xenorhabdus species were lower (<98.4 %). The two strains shared 98% 16S rRNA gene sequence similarity. Multilocus sequence analysis (MLSA) based on concatenated partial recA, dnaN, gltX, gyrB and infB gene sequences showed a clear distinction of strains 30TX1(T) and DL20(T) among each other and to the closest related type strains. DNA-DNA hybridizations between strain DL20(T) and the type strain of X. ishibashii resulted in a relatedness value of 53 %. Genome-to-genome-based comparisons gave average nucleotide identities of 93.6% (reciprocal 93.5 %) for strain 30TX1(T) and X. ehlersii DSM 16337(T), of 92.8% (reciprocal 93 %) for strain DL20(T) and X. ishibashii DSM 22670(T) and of 93.0% (reciprocal 93.2 %) for the two novel strains. The fatty acid profile of the strains consisted of the major fatty acids C-14:0, C-16:0, C-17:0 cyclo, C-16 : 1 omega 7c and/or iso-C-15:0 2-OH, and C-18:1 omega 7c. Genome-to-genome comparison and MLSA results together with the differential biochemical and chemotaxonomic properties showed that strains 30TX1(T) and DL20(T) represent novel Xenorhabdus species, for which the names Xenorhabdus thuongxuanensis sp. nov. (type strain 30TX1(T) = CCM 8727(T) = LMG 29916(T)) and Xenorhabdus eapokensis sp. nov. (type strain DL20(T) = CCM 8728(T) = LMG 29917(T)) are proposed, respectively.
