Fig. 5: Phenotypes of S. mutans strains defective in the SCC side-chain decorations.

A Sedimentation phenotype of S. mutans WT and specific mutants after overnight growth in THY broth. B Scanning electron micrographs of S. mutans WT, ΔsccN, ΔsccP, ΔsccM and ΔsccQ. Exponentially growing bacteria were fixed, dehydrated stepwise, and viewed by scanning electron microscopy (SEM). Orange arrows denote the cells with skewed division planes. Green arrows denote cells with irregular size. Scale bar is 1 µm. Representative images from at least three independent experiments are shown in A and B. C Distribution of cell length of cell population at mid-log growth phase for WT and ΔsccQ. DIC images of bacterial cells were analyzed using the software ImageJ, ObjectJ plugin to quantify cell length and width. Total number of cells was n = 144 for WT, n = 198 for ΔsccQ. Box plots show the median value (middle line), and 25%, 75% quartiles (boxes), and whiskers represent 5 – 95 percentile. P values were determined by unpaired two-tailed t-test with Welch correction. Cell size analysis is presented in Supplementary Table 3. D Protein-based biofilm formation by S. mutans strains. Biofilms were incubated in UFTYE medium supplemented with 1% d-glucose for 24 h at 37 °C in presence of 5% CO₂ and analyzed as outlined in Methods by crystal violet assay (Abs 540 nm). Column and error bars represent the mean ± S.D. of three independent biological experiments. Significant differences (P < 0.05) are determined by one-way ANOVA with Dunnett’s multiple comparisons test. Image of biofilms formed by S. mutans strains after crystal violet staining is representative image of three independent biological experiments. Source data for D are provided as a Source data file.