Xenorhabdus

Xenorhabdus is a genus of motile, gram-negative bacteria from the family of the Morganellaceae. All the species of the genus are only known to 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 its insect host without the bacteria.

The tripartite Xenorhabdus-nematode-insect interaction represents a model system in which both mutualistic and pathogenic processes can be studied in a single bacterial species. In the laboratory, some species are virulent even when artificially injected into the insect host, whereas others species need the nematode to affect the insect.