Expression of PtoxA in the wild-type, ptxS and ptxR deficient backgrounds.

The promoter region of toxA or kgu was cloned into pMP220 (TcR) and the resulting plasmid electroporated into the indicated strains. Cells were grown on M9 minimal medium with citrate (15 mM) and overnight cultures were diluted 50-fold in the same medium in the absence or in the presence of 2-ketogluconate (5 mM). β-galactosidase activity was determined in cells in the exponential phase of growth after 3 hours of incubation. Data are the average of 3 independent assays each performed in duplicate.将toxA或kgu的启动子区域克隆至携带四环素抗性标记（TcR）的pMP220质粒中，将构建得到的重组质粒通过电转化法导入指定菌株。将细胞接种于添加15 mM柠檬酸盐的M9基础培养基中培养，过夜培养液按50倍稀释至相同培养基中，分别在不含和含有5 mM 2-酮葡糖酸（2-ketogluconate）的条件下继续培养。孵育3小时后，对处于指数生长期的细胞进行β-半乳糖苷酶（β-galactosidase）活性测定。实验数据为3次独立重复实验的平均值，每次实验均设置2个平行复样。