C. elegans relies on odors to select leucine-enriched bacteria.

(A) Schematic representation of ‘odor-only’ diet preference assay.

Preference index (PI) of WT worms in an ‘odor-only’ diet preference assay (indicated as ) for individual diet supplemented with (B) 5 mM leucine (+ LEU), (C) 5 mM isoleucine (+ ILE), and (D) 5 mM valine (+ VAL). Error bars indicate SEM (n≥15). Also see Figure S1.

Leucine supplementation boosts isoamyl alcohol levels via Ehrlich degradation pathway.

GC-MS/MS profile of odors produced by CEent1 under (A) leucine supplemented and (B) leucine unsupplemented conditions. Unmarked peaks represent masses contributed by fiber or media alone (n≥3).

(C) Heat map representing the relative abundance of various odors in the headspace of CEent1, JUb66, and BIGb0170 with and without leucine supplementation.

(D) Absolute abundance of IAA (in moles) produced by CEent1 under leucine supplemented and unsupplemented conditions. * P ≤ 0.05 as determined by a two-tailed unpaired t-test.

(E) Schematic of Ehrlich degradation pathway.

(F) Fold change of transcript levels of ilvE under leucine supplemented over unsupplemented conditions for CEent1.

Error bars indicate SEM (n≥3).

Odors sensed through AWC neurons mediate the diet preference of C. elegans.

Preference index (PI) of WT, odr-7, and AWC(-) worms for (A) CEent1, (B) JUb66, and (C) BIGb0170 supplemented with leucine over unsupplemented conditions. symbol indicates ‘odor-only’ preference assays. Chemotaxis index (CI) of WT, odr-7, and AWC(-) worms for (D) isoamyl alcohol (IAA), (E) acetoin (ACE),

(F) isovalerate (ISV), (G) isobutanol (ISB), (H) phenylethyl alcohol (PEA), (I) butyl acetate (BA), and (J) methyl isovalerate (MIV)

(K) Summary schematic representing the role of AWA and AWC odor sensory neurons in ‘odor-only’ diet preference for leucine-enriched diets and chemotaxis assays.

Significant differences are indicated as * P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001, and **** P ≤ 0.0001 determined by one-way ANOVA followed by post hoc Dunnett’s multiple comparison test. Error bars indicate SEM (n=15).

Isoamyl alcohol regulates the diet preference of worms.

(A) Schematic representation of the adaptation regimen followed by chemotaxis assays.

Chemotaxis index (CI) for naïve worms and worms adapted with CEent1, JUb66, or BIGb0170 odors to (B) isoamyl alcohol (IAA), (C) acetoin (ACE), (D) isovalerate (ISV), (E) isobutanol (ISB) (F) phenylethyl alcohol (PEA), (G) butyl acetate (BA), and (H) methyl isovalerate (MIV). Dark gray bars indicate naïve worms and light gray bars indicate worms adapted to bacterial odors.

Significant differences are indicated as * P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001, and **** P ≤ 0.0001 determined by one-way ANOVA followed by post hoc Dunnett’s multiple comparison test. Error bars indicate SEM (n=15).

Robust chemoperception of isoamyl alcohol in wild isolates of C. elegans.

(A) World map representing the distinct geographical locations (source) of wild isolates of C. elegans used in this study.

Chemotaxis index (CI) of WT and wild isolates of worms for (B) IAA, (C) diacetyl (DA), (D) phenylethyl alcohol (PEA), and (E) acetoin (ACE).

Significant differences are indicated as * P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001, and **** P ≤ 0.0001 determined by one-way ANOVA followed by post hoc Dunnett’s multiple comparison test. Error bars indicate SEM (n=15).

SRD-12 GPCR mediates isoamyl alcohol sensing and diet preference in C. elegans.

(A) List of GPCRs that are highly expressed in AWC neurons. Chemotaxis index (CI) of WT and GPCR edited strains to 1:1000 IAA (n≥3).

(B) Schematic for chemotaxis assay plate used for movement track analysis.

Movement tracks of 5 animals in a chemotaxis arena with 1:1000 IAA for 15 minutes, for (C) WT, (D) VSL2401, and (E) VSL2402. Also, refer to the video S2. Individual color represents the track for a single worm.

Chemotaxis index (CI) of WT, VSL2401, and VSL2402 worms for (F) 1:1000 IAA, (G) 500 mM acetoin (ACE), and (H) absolute phenylethyl alcohol (PEA).

(I) Preference index (PI) of WT, VSL2401, and VSL2402 worms for a preferred diet, CEent1, over E. coli OP50. symbol indicates ‘odor-only’ preference assays.

Significant differences are indicated as * P ≤ 0.05, ** P ≤ 0.01, and **** P ≤ 0.0001 determined by one-way ANOVA followed by post hoc Dunnett’s multiple comparison test. Error bars indicate SEM (n≥15).

Model depicting odor-based foraging strategy used by C. elegans.

C. elegans prefers leucine-enriched diets in an odor-dependent manner. Preferred bacteria catabolize leucine, an EAA, to produce IAA via the Ehrlich degradation pathway. SRD-12 GPCR expressed in AWC odor sensory neurons mediates the foraging behavior of C. elegans by sensing IAA.