Identification of attractive odorants released by preferred bacterial food found in the natural habitats of C. elegans

Abstract

Food choice is critical for survival because organisms must choose food that is edible and nutritious and avoid pathogenic food. Many organisms, including the nematode C. elegans, use olfaction to detect and distinguish among food sources. C. elegans exhibits innate preferences for the odors of different bacterial species. However, little is known about the preferences of C. elegans for bacterial strains isolated from their natural environment as well as the attractive volatile compounds released by preferred natural bacteria isolates. We tested food odor preferences of C. elegans for non-pathogenic bacteria found in their natural habitats. We found that C. elegans showed a preference for the odor of six of the eight tested bacterial isolates over its standard food source, E. coli HB101. Using solid-phase microextraction and gas chromatography coupled with mass spectrometry, we found that four of six attractive bacterial isolates (Alcaligenes sp. JUb4, Providenica sp. JUb5, Providencia sp. JUb39, and Flavobacteria sp. JUb43) released isoamyl alcohol, a well-studied C. elegans attractant, while both non-attractive isolates (Raoultella sp. JUb38 and Acinetobacter sp. JUb68) released very low or non-detectable amounts of isoamyl alcohol. In conclusion, we find that isoamyl alcohol is likely an ethologically relevant odor that is released by some attractive bacterial isolates in the natural environment of C. elegans.

Reliability of an interneuron response depends on an integrated sensory state

“…Since the reliability of the AIA response required inputs from multiple sensory neurons, we asked whether the same logic applied for other odors. Based on previous ablation studies, chemotaxis to diacetyl requires AWA at low concentrations, with a redundant role for AWC at high concentrations (Chou et al, 2001), whereas chemotaxis to another odor and bacterial metabolite, isoamyl alcohol, requires AWC with a minor contribution from AWA (Bargmann et al, 1993; Worthy et al, 2018). Both AWC and AWA respond to isoamyl alcohol with calcium transients (Larsch et al, 2013), suggesting that study of this second odor could test the generality of the AIA activation model.…”

Host-microbe interactions and the behavior of Caenorhabditis elegans

“…Genetic analysis of chemotactic responses to diacetyl, which is produced by many bacteria, identified ODR-10 as a chemoreceptor for diacetyl (Sengupta, Chou, & Bargmann, 1996). The chemical characterization of natural bacterial isolates that may serve as food for C. elegans in the wild has further revealed a number of volatile organic compounds that attract C. elegans (Worthy et al, 2018a). Bacterial food cues modulate dauer entry and exit (Golden & Riddle, 1984), and fatty acids derived from bacteria cause dauer larvae, which do not ingest bacteria, to exit dauer diapause (Kaul et al, 2014).…”

Irrational behavior in C. elegans arises from asymmetric modulatory effects within single sensory neurons

“…1), we used stimuli that are known to attract C. elegans worms 4 . Moreover, some of these stimuli had been shown to be secreted by bacteria, upon which the worms feed 59,60 . Although the concentrations used in our assays may not reflect the typical concentrations found in the natural ecological niches, they still served as potent attractors; thus, the irrationalities reported herein are found in the context of the worms’ evolutionary-shaped innate chemotaxis behavior.…”