FIG. 3.

HtrA is essential for stress tolerance in S. mutans. (A) Freshly grown overnight cultures of NG-8 (wild type), IBS101 (htrA), and IBS101/pIB108 ((htrA/htrA⁺) were washed and 10-fold serially diluted in PBS. Ten-microliter samples were spotted on THY agar plates with nothing (37°C), puromycin (0.75 μM, PUR), or H₂O₂ (1.5 mM). (B) Cultures were spotted on THY agar plates that were buffered to generate pH 7.0, pH 6.0, or pH 5.5. (C) Cultures were spotted on THY agar containing nothing (control), NaCl (1 M), or mitomycin C (12.5 ng/ml, MC). Plates were incubated at 37°C in the presence of ambient air (A and C) or anaerobically (B). Experiments were repeated no fewer than three times and relevant areas of representative plates are shown.