End-point pH analysis and acid killing.
(A) Panel shows results of End-point pH analysis of S. mutans wildtype, UA159 and mutants deficient of Rex (TW239), GuaA (TW263) and both Rex and GuaA (JB314) grown in BM with glucose (18 mM) and sucrose (2 mM) under aerobic (grey bars) and anaerobic conditions (open bars), with * and # indicating significant differences between the wildtype and the particular mutants under the same conditions at a level of P<0.05 and P<0.001, respectively. Rex-deficiency increases the final resting pH, especially under aerobic conditions. (B) Panel illustrates survival rates of UA159 (diamond), TW239 (square), TW263 (triangle) and JB314 (circle) after acid -killing at pH 2.8 for 45 minutes. Symbols *, indicating significant difference between UA159 and JB314 at the level of P<0.01. The Rex/GuaA double mutant is approximately 2-logs more susceptible to acid than UA159.
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