PMC

Bacteria influence C. elegans behavior through differential modulation of hyperoxia avoidance and pathogen avoidance responses. The NPR-1–dependent regulation of oxygen sensation behavior by bacteria is impaired by mucoid exopolysaccharide biosynthesis, which can modulate the balance between oxygen sensing and pathogen avoidance behaviors of C. elegans.

Oxygen concentration measurements of WT and mucD P. aeruginosa PA14 lawns. Representative profiles of oxygen concentration as a function of depth throughout (A) PA14 and (B) mucD colonies. Duplicate measurements were taken at the border (yellow) and center (red) of each colony for two independent colonies. Agar (blue) alone was measured as a control. Measurements up to ∼400 μm reflect ambient oxygen concentrations before the electrode entering the colony.

C. elegans N2 does not avoid mucoid P. aeruginosa. (A) Approximately 30 L4 larval stage C. elegans N2 were placed on lawns of P. aeruginosa strains PA14, PA14 mucD, PA14 mucDalgD, and a mixed lawn of PA14 and PA14 mucD and imaged after 24 h at 25 °C. (B) Lawn occupancy of N2 worms on mucoid and nonmucoid pathogenic bacterial strains (n > 300 worms for each bacterial strain). Small lawns of bacterial strains were cultured on 3-cm plates, and L4 worms were placed in the center of each lawn. The number of animals on each lawn was counted after 24 h at 25 °C. Strains PA14, PA14 mucDalgD, and PA14 algD are nonmucoid (black bars); strains PA14 mucD, P. aeruginosa ATCC 19142, P. aeruginosa ATCC 39324, P. aeruginosa ATCC 33468, and B. cepacia ATCC 27515 are mucoid (gray bars). Error bars represent the SEM of at least 15 independent plates.

Inhibition of aerotaxis behavior modulates survival on mucoid P. aeruginosa. (A) Photograph of loss-of-function mutant gcy-35(ok769) worms cultured on a plate with the mucoid P. aeruginosa strain PA14 mucD. Approximately 30 L4 worms were placed on the lawn and photographed after 24 h at 25 °C. (B) Lawn occupancy of indicated C. elegans strains on mucoid PA14 mucD. (C) Survival curve of L4 stage N2, CB4856, and gcy-35(ok769) mutant worms on mucoid P. aeruginosa strain PA14 mucD. The assay was carried out with lawn conditions consisting of a small spot of bacteria in the center of the plate as previously described (). At least 60 worms for each genotype were assayed in two independent trials. The differences in susceptibility between N2 and gcy-35(ok769) and between CB4856 and gcy-35(ok769) are significant (P < 0.0001 for each comparison).

Reversal of NPR-1–dependent behaviors on mucoid strains of nonpathogenic bacteria. (A) Approximately 50 N2 L4 stage worms were cultured on plates and imaged after 24 h at 22 °C on bacterial lawns of the standard laboratory food source nonmucoid E. coli strain OP50, mucoid S. meliloti strain 102F34, and mucoid E. coli strain ATCC 35353. (B) Summary of bordering results obtained with indicated strains under conditions as in A. +, greater than 80% of the worms were on the border of the lawn; −, fewer than 40% of the worms were on the border of the lawn. (C) Average speed of movement of N2 and CB4856 worms on nonpathogenic bacterial lawns of the indicated strains. Black bars indicate nonmucoid strains; gray bars indicate mucoid strains. Three plates were analyzed for each data point, with at least 25 animals scored for 20 min of recording on each plate. Error bars represent the SEM.