Microbial odours activate protective immune response in Caenorhabditis elegans via specific olfactory neurons

Caenorhabditis elegans, like other animals, relies on attractive odours for foraging and on aversive odours for avoidance of pathogens. An odour produced by pathogenic bacterium Pseudomonoas aeruginosa induces immune response as well as avoidance in C. elegans via AWB olfactory neurons. We asked whether AWB neurons provide broader immunity to a wide range of pathogens. We activated AWB neurons using three chemically distinct bacterial odours and found that activation indeed induces protective immunity. Conversely, silencing of AWB neurons early during infection enhances susceptibility to infections. Mechanistic investigation revealed that the activation of AWB using odours upregulates detoxification pathways and other protective pathways in non-neuronal tissues. Specifically, odour exposure activates UDP-glucuronosyltransferase UGT-18 in the intestine that protects worms from the phenazine toxin of Pseudomonas aeruginosa and promotes broader immunity to Gram-negative bacteria (P. aeruginosa and Salmonella enterica), Gram-positive bacteria, (Enterococcus faecalis and Staphylococcus aureus), and yeast (Cryptococcus neoformans). Altogether, our findings highlights microbial odours as non-canonical molecular patterns for activating immune responses.