To construct a recombinant plasmid carrying the cholera toxin B subunit(CTB) gene and observe its expression in E.

• 目的构建霍乱弧菌肠毒素B亚单位(Cholera toxin B subunit,CTB)基因的大肠杆菌表达重组质粒,并观察其在大肠杆菌和双歧杆菌中的表达。