Xenorhabdus lircayensis sp. nov., the symbiotic bacterium associated with the entomopathogenic nematode Steinernema unicornum

Abstract

<i>Xenorhabdus</i> is a symbiotic group of bacteria associated with entomopathogenic nematodes of the family Steinernematidae. Although the described <i>Steirnernema</i> species list is extensive, not all their symbiotic bacteria have been identified. One single motile, Gram-negative and non-spore-forming rod-shaped symbiotic bacterium, strain VLS^T, was isolated from the entomopathogenic nematode <i>Steinernema unicornum</i>. Analyses of the 16S rRNA gene determined that the VLS^T isolate belongs to the genus <i>Xenorhabdus</i>, and its closest related species is <i>Xenorhabdus szentirmaii</i> DSM 16338^T (98.2 %). Deeper analyses using the whole genome for phylogenetic reconstruction indicate that VLS^T exhibits a unique clade in the genus. Genomic comparisons considering digital DNA-DNA hybridization (dDDH) values confirms this result, showing that the VLS^T values are distant enough from the 70 % threshold suggested for new species, sharing 30.7, 30.5 and 30.3 % dDDH with <i>Xenorhabdus khoisanae</i> MCB, <i>Xenorhabdus koppenhoeferi</i> DSM 18168^T and <i>Xenorhabdus miraniensis</i> DSM 18168^T, respectively, as the closest species. Detailed physiological, biochemical and chemotaxonomic tests of the VLS^T isolate reveal consistent differences from previously described <i>Xenorhabdus</i> species. Phylogenetic, physiological, biochemical and chemotaxonomic approaches show that VLS^T represents a new species of the genus <i>Xenorhabdus</i>, for which the name <i>Xenorhabdus lircayensis</i> sp. nov. (type strain VLS^T=CCCT 20.04^T=DSM 111583^T) is proposed.