Abstract
Nitric oxide (NO) is released into the air by NO-producing organisms; however, it is unclear if animals utilize NO as a sensory cue. We show that C. elegans avoids Pseudomonas aeruginosa (PA14) in part by detecting PA14-produced NO. PA14 mutants deficient for NO production fail to elicit avoidance and NO donors repel worms. PA14 and NO avoidance are mediated by a chemosensory neuron (ASJ) and these responses require receptor guanylate cyclases and cyclic nucleotide gated ion channels. ASJ exhibits calcium increases at both the onset and removal of NO. These NO-evoked ON and OFF calcium transients are affected by a redox sensing protein, TRX-1/thioredoxin. TRX-1's trans-nitrosylation activity inhibits the ON transient whereas TRX-1's de-nitrosylation activity promotes the OFF transient. Thus, C. elegans exploits bacterially produced NO as a cue to mediate avoidance and TRX-1 endows ASJ with a bi-phasic response to NO exposure.
Highlights
Nitric oxide (NO) is an important signaling molecule in both prokaryotes and eukaryotes
By contrast, when feeding on a pathogenic bacterial strain (e.g. P. aeruginosa PA14), C. elegans avoids the pathogen by foraging off the bacterial lawn (Reddy et al, 2009; Styer et al, 2008)
PA14 avoidance is contingent on the virulence of the bacterial strain, as an isogenic PA14 gacA mutant, which is significantly impaired in its ability to kill C. elegans (Tan et al, 1999), failed to elicit avoidance of the bacterial lawn (Figure 1C)
Summary
Nitric oxide (NO) is an important signaling molecule in both prokaryotes and eukaryotes. NO regulates key physiological events, such as vasodilation, inflammatory response, and neurotransmission (Feelisch and Martin, 1995). NO regulates innate immunity and life span in the nematode C. elegans (Gusarov et al, 2013), as well as virulence and biofilm formation in different bacteria (Cutruzzolaand Frankenberg-Dinkel, 2016; Shatalin et al, 2008). As a reactive oxygen species, NO covalently modifies the thiol side chain of reactive cysteine residues (forming S-nitrosylated adducts), thereby modulating the activity of these proteins (Foster et al, 2003). NO can bind to the heme co-factor associated with soluble guanylate cyclases (sGCs), thereby stimulating cGMP production and activating downstream cGMP targets (Denninger and Marletta, 1999)
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