Fig. 3

ROS negatively impacts biofilm development through the DDR induction. a The biofilm formed by a Δsda strain is more robust than the isogenic parental strain. Comparison of the biofilm (both colony and pellicle) phenotypes between the parental strain (NCIB 3610) and the isogenic Δsda mutant strain (YCN025). Right-hand panels show zoom-in images of the pellicle biofilms shown in the middle panels. Biofilms were incubated at 30 °C for 48 h before the images were taken. From left to right, scale bar represents 1, 2.5, and 0.6 mm, respectively. b Matrix gene expression is stronger and more uniform in colony biofilms of the Δsda mutant strains. Colony biofilms formed by the wild-type strain, the Δsda, the ΔlexA, and the Δsda ΔlexA double mutant strains with the P _tapA -mKate2 reporter. Colony biofilms were grown on LBGM agar plates at 30 °C for 24 h prior to imaging. Scale bar represents 1 mm. c Quantification of matrix gene expression. β-Galactosidase activities of the P _tapA -lacZ matrix reporter in the wild type, the Δsda mutant, the ΔlexA mutant, and the Δsda ΔlexA double mutant strains were assayed in LBGM shaking culture. Assays were performed in triplicate using mid-exponential cells and following published protocols.²⁵ A two-tailed student’s t-test was used to determine statistical significance between each mutant and the wild-type strain (* indicates p-value < 0.05). d UV treatment triggered DNA damage lowered matrix gene expression. The dual reporter cells (P _yneA -gfp, P _tapA -mKate2) of the wild-type and the ΔlexA mutant strains were treated with UV light, and examined by fluorescence microscopy after 1 h. Green cells express the DDR P _yneA -gfp reporter while red cells express the matrix P _tapA -mKate2 reporter. Scale bar represents 10 μm