Fig 4.

Correlation between Congo red binding by and curli gene (csgA) expression in the wild-type and hha mutant at 37°C and 30°C. Congo red binding was assessed based on the intensity of the red color of the colonies produced on YESCA agar containing Congo red after incubation for 24 h at 37°C (A) or after incubation for 48 h at 30°C (C). Coloration of the colonies was interpreted as light red (low), dark red (intermediate), or darker red (high). The expression of csgA, the gene encoding curlin of curli fimbriae, was determined by QRT-PCR using DNA-free RNA prepared from the wild-type, hha mutant, and hha⁺/hha mutant strains grown at 37°C (B) and 30°C (D). Bars with different hatching patterns represent the average relative expression of csgA determined using RNA from three independent bacterial cultures grown at 37°C (B) and 30°C (D). Error bars represent the SEM. Significant (P < 0.05) differences between the wild-type and mutant strains were determined using an unpaired Student's t test and Welch's correction. **, P = 0.004; ***, P < 0.0001.