Organismal traits are often the product of interactions between the organism and its microbial symbionts. Symbionts can provide their host access to vital nutrients, increase abiotic tolerances of their host, and provide defense against pathogens and predators. Xenorhabdus symbionts of Steinernema nematodes produce many compounds which help in killing and digesting the insect host and are key for successful reproduction of the nematode. Xenorhabdus bacteria also produce a suite of secondary metabolites and defensive compounds that protect the insect cadaver from fungal and bacterial saprophytes.
In addition to the broad-spectrum defenses, the bacteriocins produced by Xenorhabdus can help their nematode partners gain a competitive advantage over co-infecting nematodes. Despite this benefit, several natural isolates of Xenorhabdus are not able to inhibit any sympatric isolates. Does this represent recent evolution of resistance? Or, could these isolates be following a different path to success? Evidence suggests that these isolates may be better at parasitizing the insect host, leading to a higher probability of successful emergence by the nematode and bacterial partners.
