Objective This study aims to evaluate the effect of ptxA and ptxB genes, which are important genes in the L-ascorbate phosphotransferase system (PTS) ofStreptococcus mutans(S. mutans). Methods The ptxA-, ptxB-, and ptxABdouble deficient mutant as well as ptxAB-complemented strain were constructed. Quantitative real-time polymerase chain reaction analysis was performed to evaluate the expression of the target genes of wild-typeS. mutanswhen L-ascorbate was used as the sole carbohydrate source. The OD600values of the wild type, deficient, and complemented strains were continuously monitored, and their growth curves were constructed to compare growth capacity. Results Polymerase chain reaction and sequencing analyses suggested that deficient and complemented strains were successfully constructed. The expression levels of ptxA and ptxB significantly increased (PS. mutans. The construction of deficient strains and complemented strain lay a foundation for further mechanism study on L-ascorbate metabolism inS. mutans.
