Xenorhabdus bakwenae sp. n., associated with the entomopathogenic nematode Steinernema bakwenae

Abstract

Summary The bacterial strain SF857 was isolated from the entomopathogenic nematode, Steinernema bakwenae SF857, found in soil samples of St Lucie cherry, a species of cherry tree, from the Muriti farm, close to Kroondal (25°44′E, 59°99′S) in the northwest province of South Africa. Strain SF857 is Gram-negative, catalase and oxidase-negative, and lecithinase-positive. Strain SF857 shared the highest 16S rRNA gene sequence similarity (97.7%) with the type strain of Xenorhabdus ishibashii. However, a comparison of housekeeping gene sequences showed that strain SF857 grouped closer to X. griffiniae, X. ehlersii and X. thuongxuanensis than to X. ishibashii. Digital DNA-DNA hybridisation (dDDH) between strain SF857 and all Xenorhabdus spp. is less than the 70% species threshold, confirming that the strain belongs to a separate species. Furthermore, the biochemical characteristics of strain SF857 differ from other Xenorhabdus spp. Based on these findings, strain SF857 represents a novel species within the genus Xenorhabdus, for which the name Xenorhabdus bakwenae sp. n. (type strain SF857T) is proposed. Pathogenicity bioassays with last-instar Cydia pomonella showed S. bakwenae to be highly virulent, with potential use as a biocontrol agent in apple orchards.