Supplementary Material for: <b><i>Streptococcus salivarius</i></b> Isolates of Varying Acid Tolerance Exhibit F₁F₀-ATPase Conservation

Genes encoding the subunits of the membrane-bound F1F0-ATPase (responsible for exporting protons from the cytoplasm and contributing to acid tolerance) were sequenced for 24 non-mutans streptococci isolated from carious lesions. Isolates, mostly Streptococcus salivarius, displayed a continuum of acid tolerance thresholds ranging from pH 4.55 to 3.39, but amino acid alignments of F1F0-ATPase subunits revealed few non-synonymous substitutions and these were unrelated to acid tolerance. Thus, the F1F0-ATPase is highly-conserved among S. salivarius isolates despite varying acid tolerance thresholds, supporting the contention that acid tolerance is determined by the level of gene/protein expression rather than variation in molecular structure.本研究对24株从龋损病灶（carious lesions）中分离的非变形链球菌（non-mutans streptococci）的膜结合F1F0-ATP合酶（membrane-bound F1F0-ATPase，负责将质子从细胞质中排出并参与酸度耐受）的亚基编码基因进行了测序。本次研究的分离株大多为唾液链球菌（Streptococcus salivarius），其酸度耐受阈值呈连续谱系分布，区间范围为pH 4.55至3.39；但对F1F0-ATP合酶亚基进行的氨基酸序列比对分析显示，仅存在少量非同义替换（non-synonymous substitutions），且此类替换与酸度耐受并无关联。综上可见，尽管不同分离株的酸度耐受阈值存在差异，但F1F0-ATP合酶在唾液链球菌分离株中呈现高度保守性，该结果支持了“酸度耐受由基因/蛋白质表达水平而非分子结构变异决定”的学术观点。