Xenorhabdus

Xenorhabdus is a genus of motile, gram-negative bacteria from the family of the Enterobacteriaceae. It has the particularity that all the species of the genus live in symbiosis with soil entomopathogenic nematodes from the genus Steinernema.

Although no free-living forms of Xenorhabdus have ever been isolated outside of the nematode host, the benefits for the bacteria are still unknown. However, it has been demonstrated that the nematode can't establish within his insect host without the bacteria.