Pathogen derived volatiles modulate flight or fight response in Caenorhabditis elegans

Abstract

In nature, the interaction between two organisms largely relies on their ability to sense and respond to each other, which involves many specific chemicals and signaling pathways. Animals have evolved mechanisms to detect pathogens in their environment and alter their behavior and physiology to avoid infection. In this work, I have studied the nematode Caenorhabditis elegans and its interaction with a bacterial pathogen Pseudomonas aeruginosa PA14 to define the molecular basis of olfaction-driven changes in host behavior and physiology. C. elegans is a bacterivore that forages in decaying organic matter for food. A well-developed chemosensory system including an odor sensory system enables C. elegans to efficiently engage in food search behavior as well as to avoid pathogens. C. elegans exhibits both flight and fight response to P. aeruginosa, a ubiquitous bacterium, and an opportunistic human pathogen. In the first part of my work, we explore the innate ability of C. elegans to respond to P. aeruginosa volatiles. In a systematic study of behavioral response, we find that C. elegans avoid old lawn of P. aeruginosa a flight behavior termed aversion response. Using olfaction defective mutant worms odr-3(n2150) we first show that the volatile cues from the pathogenic lawn majorly drive the avoidance response of the host. Also, this olfaction-mediated aversion response helps the host to increase its chances of survival when exposed to the pathogen. Using solid-phase microextraction (SPME) based gas chromatography-mass spectrometry (GC-MS), we identify six prominent volatiles released by the aversion-inducing old lawn of P. aeruginosa. Dimethyl sulfide, dimethyl disulfide, pyrrole, 1,4-dichlorobenzene, hexanoic acid, 2-ethyl-, methyl ester, and 1-undecene are abundantly present in the P. aeruginosa headspace. By using odor sensory mutants of C. elegans and specific volatiles from P. aeruginosa in chemotaxis assays, we find that C...