Objective To evaluate the effect of SMU.2055 gene on acid resistance of Streptococcus mutans. Methods A SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique. The growth of the wild-type and mutant strains was monitored in both normal and acidic conditions. The lethal pH level, glycolysis, proton permeability, cell permeability and biofilm formation of the two strains were compared. Results PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. The growth and biofilm formation capacity of the mutant strain were obviously lowered in both normal and acidic conditions. The mutant strain also showed increased lethal pH level, proton permeability, and cell permeability with impaired H+-ATPase activity in acidic conditions, but its minimum glycolytic pH remained unaffected. Conclusion The SMU.2055-deficient S. mutans mutant exhibits a lowered acid resistance, which affects the growth, lethal pH, proton permeability, H +-ATPase activity, cell permeability and biofilm formation but not the minimum glycolytic pH of the mutant strain.%目的 针对变异链球菌(S.mutans)UA159构建SMU.2055基因缺陷菌株,研究SMU.2055基因对S.mutans耐酸能力的影响.方法 利用同源重组的方法,构建SMU.2055基因缺陷菌株.连续监测野生菌株和基因缺陷菌株在不同pH值环境中菌液的A600值,比较在不同pH值条件下的生长能力.将两种菌株转入一组pH值跨度为2.5～7.0的BHI培养基,厌氧培养3 h,观察其致死性pH值.加入过量的葡萄糖,检测两种菌株糖酵解能力.制备通透细胞,分别检测两种菌株的细胞通透性、质子通透性和H+-ATPase活性.激光共聚焦显微镜下观察两种菌株生物膜形成能力.结果 与野生菌株相比,SMU.2055基因缺陷菌株早期生长活性、pH5.5时H+-ATPase活性、生物膜形成能力均明显下降,致死性pH值、质子通透性、细胞通透性均明显升高,糖酵解能力未见明显变化.结论 SMU.2055基因与S.mutans的耐酸性作用相关.SMU.2055基因缺陷菌株耐酸能力的降低与其致死性pH值、细胞通透性、质子通透性、H+-ATPase活性、生物膜的形成有关,与其糖酵解能力无关.对研究SMU.2055基因功能奠定基础.
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