Objective: This study aims to evaluate the effect of ptxA and ptxB genes, which are important genes in the L-ascorbate phosphotransferase system (PTS) of Streptococcus mutans (S. mutans).
Methods: The ptxA-, ptxB-, and ptxAB-double 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-type S. mutans when L-ascorbate was used as the sole carbohydrate source. The OD₆₀₀ values 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 levelsof ptxA and ptxB significantly increased (P < 0.01) when L-ascorbate was used as the sole carbohydrate source. The growth capacity of the deficient mutants decreased compared with that of the wild-type strain. However, the wild-type phenotype could be restored in the complemented strain.
Conclusion: ptxA and ptxB genes are associated with L-ascorbate metabolism of S. mutans. The construction of deficient strains and complemented strain lay a foundation for further mechanism study on L-ascorbate metabolism in S. mutans.
目的: 研究变异链球菌（S. mutans）磷酸转移酶系统（PTS）中抗坏血酸家族ptxA、ptxB基因对细菌生长能力的影响。
方法: 构建ptxA、ptxB和ptxAB双重基因缺陷菌株以及ptxAB功能补偿菌株。在仅以抗坏血酸作为唯一碳源时，使用实时荧光定量聚合酶链反应检测野生株中ptxA、ptxB基因的表达情况。连续监测野生株、缺陷株和补偿株的菌液OD600值，比较其生长能力。
结果: 经过聚合酶链反应和测序鉴定，结果证明缺陷株和补偿株构建成功。在以抗坏血酸作为唯一碳源的培养基中，野生株ptxA、ptxB基因的表达量均明显增高（P<0.01）。缺陷株的生长能力较野生株有所下降，但是在补偿株中可以得到补偿。
结论: ptxA、ptxB基因与S. mutans对抗坏血酸的吸收利用密切相关，缺陷株和补偿株的构建为进一步研究目的基因在S. mutans抗坏血酸代谢中的作用机制提供了理论基础。