First, we examined the overall structural

characteristics of biofilms formed after 24 h using CLSM (Figure 2d-f; Additional file 1: Figure S1a-f). The average biofilm thickness (see Methods section) differed among all three strains with M1 producing considerably thinner biofilm (mean value of 9 μm) compared to M28 (12 μm) and M41 (15 μm), a result consistent with lower spectrophotometric absorbance values (Figure 1a). In addition to measured differences in biofilm thickness, closer examination of the X-Y orthogonal Z-stack views, representing biofilm cross-sections, revealed architectural differences among the M41, M28, and M1 biofilms. The M1 biofilm, selleck products although the thinnest, seems to consist of densely-packed cells that form continuous layers, while the M28 and especially M41 biofilms seem to be less dense but exhibit more elevated supracellular assembly. We therefore used field emission scanning electron microscopy (FESEM) Selleck GDC-0994 to define more accurately these supracellular differences observed by CLSM between the biofilms produced by the WT M1 and

M41 GAS (Figure 3). FESEM exposed notable architectural differences between biofilms formed by these two strains. The M41 (Figure 3, panel a) biofilm was characterized by more diverse surface architecture with the evidence of depressions or crypts, whereas the M1 biofilm (panel b) seems to lack such pronounced surface characteristics. At higher magnification, the M41 cells have a studded cell surface morphology with protrusions linking both sister cells and cells in adjacent chains (panel c). In contrast, the M1 cells had Histone Methyltransferase inhibitor a relatively smoother appearance likely due to the rich bacterial-associated extracellular matrix (BAEM) surrounding these cells and covering their surface (panel d). BAEM material, which was clearly seen at higher resolution between the M1-type cells, was not as evident between cells of the M41-type GAS. Figure 2 Biofilm formation by wild type and scl1 -inactivated isogenic mutants.

Crystal violet staining and confocal laser scanning microscopy (CLSM) of the GFP-expressing GAS were used to compare biofilm Resveratrol formation by GAS strains. Wild type (WT) M41-, M28-, and M1-type strains, scl1-inactivated mutants (scl1), and M41 mutant complemented for Scl1.41 expression (M41 C) were used. (a-c) Isogenic GAS strains were grown under static conditions for 24 h and bacterial biomass was detected spectrophotometrically at indicated time points following crystal violet staining. Absorbance values at OD600 are representative of at least three experiments performed in quadruplicate. Statistical significance is denoted as *P ≤ 0.05 and **P ≤ 0.001. (d-f) CLSM analysis of corresponding 24 h biofilms from same experiment. Images are X-Y orthogonal Z-stack views of WT (top) and mutant (bottom) GAS strains. Views are representative of ten images within a single experiment.