Investigating the mechanisms and specificity of bacterial virulence in an entomopathogenic symbiosis

Microbial symbionts contribute to the health of their host in both positive and negative ways. In the Steinernema nematode symbiosis, Xenorhabdus symbionts traditionally mediate insect virulence by producing toxins and other virulence proteins against the insect prey that they both need for sustenance. In this work, I took a bidirectional approach to the question: what is the larger role of Xenorhabdus in virulence against insect prey? 1) I investigated a novel protein family, typified by the Xenorhabdus bovienii polymorphic protein (Xbpp) with strain-level protein diversity. I found that Xbpp contributes to X. bovienii virulence in a Manduca sexta tobacco hornworm insect model. 2) I sequenced the microbiome of S. scapterisci, a nematode associated with a symbiont, X. innexi, that has notably low virulence relative to other Xenorhabdus. I found that the S. scapterisci microbiome shares many members with the Steinernema frequently associated microbiome proposed by Ogier et al. (2020). This community changed depending on the insect host through which the IJs were propagated. Overall, I found that Xenorhabdus insect virulence is highly dynamic and may include associations with additional microbial community members that contribute to the parasitic lifestyle of the Steinernema-Xenorhabdus complex.