A Phylogenetic Hypothesis on the Evolution and Interactions of Xenorhabdus Spp. (Gamma-Proteobacteria) and Their Steinernema Hosts (Nematoda: Steinernematidae)

Abstract

Nematodes in the genus Steinernema (Nematoda: Steinernematidae) and their associated bacteria Xenorhabdus spp. (Gamma-Proteobacteria) are an emergent model of terrestrial animal-microbe symbiosis. Although interest in this association initially arose out of their potential as biocontrol agents against insect pests (Tanada and Kaya, 1993), this mutualistic partnership is currently viewed more broadly under the umbrella of basic sciences to inform ecology, evolution, biochemistry, molecular, among other disciplines (Burnell and Stock, 2000; Forst and Clarke, 2002).Despite advances in the discovery and field application of this nematode-bacterium partnership, and the growing popularity of this model system, relatively little has been published to uncover the evolutionary facets of their association. This study adds to the body of knowledge regarding nematode-bacteria symbiosis by 1) producing novel, multi-gene phylogenies for Steinernema and Xenorhabdus; 2) proposing a possible scenario for historical association in the form of a cophylogenetic hypothesis; 3) describing a newly discovered Steinernema species from France.