McGowan, Natalie, Serkin, William, Sevedolmohadesin, Maedeh, Venkatachalam, Vivek, Stumbur, Stephanie, Apfeld, Javier, Schiffer, Jodie
[
International Worm Meeting,
2021]
Hydrogen peroxide is a pervasive chemical weapon used by many species to damage their prey or to protect themselves from their pathogens. Cells rely on conserved defense mechanisms, including catalases, to avoid the damage that hydrogen peroxide inflicts on their macromolecules We recently discovered that C. elegans represses those defenses in response to sensory perception of E. coli, the nematode's food source in the lab, because E. coli can deplete hydrogen peroxide from the local environment and thereby protect the nematodes1. Here, we investigated the extent to which C. elegans can tell the difference between bacteria that provide hydrogen peroxide protection and bacteria that do not. To address that question, we determined the extent to which hydrogen peroxide modulates the behavior of C. elegans in food lawns of wildtype E. coli and mutant E. coli unable to degrade hydrogen peroxide. In the absence of hydrogen peroxide in the environment, C. elegans did not exhibit a preference between these two bacteria stains. However, in the presence of hydrogen peroxide, C. elegans remained on the wildtype bacteria lawn but was much more likely to leave the lawn of the bacteria that do not degrade hydrogen peroxide. This nematode behavior was conserved when we used catalase-positive and catalase-negative bacterial strains from the natural C. elegans microbiome, suggesting that this decision-making occurs in the natural environment. To determine how C. elegans senses and responds to bacteria and environmental hydrogen peroxide, we measured calcium dynamics in ciliated sensory neurons. We identified several neuronal classes that respond to hydrogen peroxide in a bacteria-dependent manner. In addition, genetic analysis showed that serotonin signaling regulates this nematode behavior. Our findings demonstrate that the cross-kingdom interactions between C. elegans and bacteria in their microbiome determine the nematode food-leaving behavior via serotonergic signaling, enabling nematode populations to find safety from hydrogen peroxide. 1. Schiffer JA et al. (2020). Caenorhabditis elegans processes sensory information to choose between freeloading and self-defense strategies. eLife.