FIG 6.

Sortase A deficiency on eDNA production. (A) For quantitative analysis, S. mutans UA159, the sortase A-deficient mutant SAB102, and its complement strain, SJ271, which carries a wild-type copy of srtA in a multicopy shuttle vector, pDL271, were grown in the chemically defined medium FMC with glucose (20 mM) for 5-h cultures (−5) or in FMC with glucose (18 mM) plus sucrose (2 mM) for 24-h (−24) and for biofilm (−B) cultures. Biofilms were grown on HA discs that were vertically deposited in wells of 24-well plates. The eDNA in the cell-free supernatant was further normalized and expressed relative to levels for wild-type UA159. Data presented represent averages (± standard deviations) from more than 3 independent experiments, with * and ** indicating statistical difference at P < 0.01 and P < 0.001, respectively, compared to UA159 under the same conditions. Similar results were also obtained during growth in BM. (B) FE-SEM analysis of wild-type S. mutans (UA159) and the SrtA-deficient mutant (SAB102) biofilms on HA discs during growth in BM-glucose. Compared to the wild type, the SrtA-deficient mutant SAB102 consistently displayed few or no eDNA nanofibers in biofilms grown for 24 h. Images were taken at a magnification of 20,000×.