The bacterial symbiont Xenorhabdus poinarii (Enterobacteriaceae) is harbored by two phylogenetic related host nematodes: the entomopathogenic species Steinernema cubanum and Steinernema glaseri (Nematoda: Steinernematidae)

Xenorhabdus symbionts were isolated from infective juveniles of Steinernema cubanum, an entomopathogenic nematode isolated in western Cuba. A polyphasic approach, including phenotypic tests, restriction polymorphism analysis of PCR-amplified 16S rRNA genes and DNA-DNA hybridizations with determination of the Δ T m, was used to characterize this Xenorhabdus isolate. All methods converged to the conclusion that the isolate was a strain of Xenorhabdus poinarii. Until today, this species was only isolated from Steinernema glaseri and was considered to be specific to this nematode species. From the closely phylogenetic relatedness of S. cubanum and S. glaseri, which is supported by morphological and genotypic similarities, one can assume that the divergence of these two species is relatively recent. The speciation of the respective symbiotic bacteria may be in course, but at the present time, phenotypic and genotypic divergence is not sufficient to delineate two Xenorhabdus species.