胞苷是一种重要的抗肿瘤、抗病毒药物的中间体。传统的胞苷生产菌的育种策略多采用物理或化学诱变的方法，结合代谢产物类似物的抗性筛选手段，得到能够有效积累胞苷的菌株。随着分子生物学的发展，利用基因敲除技术，通过阻断细胞的代谢旁路或引入突变位点，能够有效改变目的产物的产量或质量。对代表性的胞苷生产菌株枯草芽孢杆菌和大肠杆菌的胞苷生物合成途径进行分析，并对其分子生物学育种策略进行了综述。

Cytidine is an important intermediate for antitumor or antiviral drugs. Traditional method for screening of cytidine producing strain was generally based on physical or chemical mutation combined with resistance screening method of metabolic product analogues to obtain high yield strain. With the development of molecular biology technology, the yield or quality of target product can be effectively improved by gene knockout technology to block cell metabolic pathways or introduce mutant site. In this study, the biosynthetic pathways of cytidine in B. subtilis and E. coli were analyzed, and the breeding strategy for cytidine production strain was reviewed.