Mind-Altering Microbes: How Gut Bacteria Influence Development and Behavior of Animal Hosts

Nematodes are effective models for understanding the molecular bases of animal-microbe interactions, including how bacterial products impact animal development and behavior. Steinernema hermaphroditum nematodes engage in a specific symbiosis with the bacterium Xenorhabdus griffiniae, which provides a food source and virulence vector in insects. In turn, the nematodes provide a vehicle to move bacteria between insect hosts. Previous studies demonstrated how nematodes grown on bacteria with mutations in the gene encoding the stress-response transcription factor RpoS showed differences in egg-laying behavior compared to wild-type controls. The Xenorhabdus RpoS regulon includes the highly conserved hpaBC locus, encoding enzymes that could act on metabolic intermediates of the neurotransmitter dopamine. We hypothesized that varying levels of rpoS and hpaBC in X. griffiniae will alter nematode development and egg-laying. To test this hypothesis, we created X. griffiniae strains with arabinose-tunable rpoS and hpaBC expression and then grew S. hermaphroditum on lawns of these strains with and without arabinose present. Arabinose induction of rpoS and hpaBC produced significant changes in nematode length and across treatment conditions. Preliminarily, we also found that increased HpaBC expression decreased egg-laying behaviors. These results suggest RpoS and HpaBC may regulate behavior and development in animal hosts.