Nature (2020)

Pathogenic bacteria can alter the olfactory behavior of the nematode Caenorhabditis elegans, and O’Donnell et al. have now found that commensal gut bacteria can do so as well. Among several commensal strains, the authors found that ingestion of Providencia alcalifaciens strains including JUb39 by the worms led to decreased avoidance of the repellant 1-octanol. Metabolomic analysis showed that Providencia produce tyramine, a biogenic amine involved in octanol avoidance. However, neuronally produced octopamine via a host hydroxylase enzyme, not its precursor tyramine, was found to be necessary for the JUb39-mediated decrease in octanol avoidance. Examination of C. elegans mutants defective for tyramine production from tyrosine and octopamine production from tyramine suggests that tyramine produced by the bacteria is converted to octopamine by the worms. The authors further showed that octopamine acts on the neuronal OCTR-1 octopamine receptor to mediate the JUb39-mediated response to octanol, and this microbe–host interaction leads to preferential selection of these bacteria by the worms. These results define a mechanism by which bacteria modulates host sensory behavior to promote the fitness of both organisms.