Figure 1: OxyS-expressing E. coli has a physiological impact on C. elegans.

(a) The four E. coli strains could be found by N2 worms equally well as food sources. N=40 worms for each group. Setup for the 'food quality assay' (using K12 as an example for the E. coli strain tested) is shown in the right panel. (b) Real-time PCR (left) and semi-quantitative reverse transcriptase–PCR (right) revealed OxyS expression levels of K12, OxyS, OxyR, ΔOxyS and K12 E. coli treated with 60 μM H₂O₂. (c) N2 worms were repelled from OxyS-expressing E. coli (OxyR and OxyS E. coli) in the food comparison assays, whereas OxyS deletion mutant E. coli (ΔOxyS) showed no effect. N=36 worms for each group. Setup for the 'food comparison assay' (using OxyS and K12 as examples for the two strains compared) is shown in the right panel. (d) N2 worms fed with OxyS-expressing E. coli showed decreased ability in finding OP50 food. Setup for the 'food searching assay' is shown in the right panel. N=50 worms for each group. (e) N2 worms fed with OxyS-expressing E. coli showed decreased chemotaxis to NaCl. Setup for the 'chemo-attractive assay' with NaCl gradient is shown in the right panel. (f) N2 worms fed with OxyS-expressing E. coli showed decreased chemo-avoidance to copper acetate. Setup for the 'chemo-avoidance assay' with copper acetate barrier is shown in the right panel. N=30 worms in e, f. N2 worms fed continuously (48 h) with the respective E. coli strain were used, and data from che-2 worms fed with OP50 were also shown in d–f. (g–i) Chemosensory ability impaired by OxyS could be restored gradually when food with OxyS expression was replaced by food without OxyS expression (K12) examined with food searching assays (g), chemo-attractive assay with NaCl gradient (h) and chemo-avoidance assay with copper acetate barrier (i). N=40 worms for g–i. L4 worms were used for all behavioural assays. P values were determined with two-tailed Student's t-test. *P<0.05; **P<0.01. All data are from three repeats. Error bars represent s.e.m.