克雷伯氏肺炎杆菌是一种重要工业微生物，菌细胞表面具有荚膜结构，荚膜对于菌株的生理特性和工业应用具有重要的影响。Rcs磷酸化信号系统是一种对菌株荚膜合成具有调控作用的信号系统。利用Red同源重组技术，分别构建了基因rcsA, rcsB缺失的菌株，还构建了基因rcsA, rcsB单独过表达的菌株。这些菌株的生理特性的研究结果表明，rcsA及rcsB基因的缺失会显著降低荚膜合成水平，进而提高外源DNA的转化细胞的效率。rcsA及rcsB缺失菌株分别在以葡萄糖和甘油为碳源的培养基中培养时，菌体更易从发酵液中进行分离，主要代谢产物2,3-丁二醇和1,3-丙二醇的产量均有少量提高。rcsA和rcsB基因的过表达均抑制菌株生长，降低外源DNA的转化细胞的效率。相对于野生菌，过表达的菌胞外多糖的含量提高，发酵液的黏度增加，rcsA过表达菌株胞外多糖的含量达到了10.33 g/L，是野生菌的5倍。通过调控rcsA及rcsB基因的活性可调控菌株荚膜多糖的合成，进而影响菌株细胞沉降、代谢物合成、胞外多糖含量等多方面的生理特性。

Klebsiella pneumoniae, capsulated bacterium, is an important industrial microorganism. Roles of the Rcs phosphorelay system on K. pneumoniae capsular polysaccharide synthesis were investigated in this work. In this research, rcsA and rcsB in K. pneumoniae were knocked out individually with the Red recombinase assisted gene replacement method. Capsule synthesized by K. pneumoniae ΔrcsA and K. pneumoniae ΔrcsB were both weak, therefore the transformation efficiency of cells was significantly increased. When these two strains were cultured with glucose or glycerol as a main carbon source, the yields of 2,3-butanediol or 1,3-propanediol produced by the cells were both higher than that of the wild-type strain. Cells of the two strains were more likely to agglutinate in the broth, which is favored for the downstream process. rcsA and rcsB over-expression strains were constructed, and the growth of the two strains were both slower than the wild-type strain. The transformation efficiency of rcsA and rcsB over-expressing strains both decreased compared with the wild-type strain. The titer of extracellular polysaccharide and the viscosity of fermentation broth of rcsA or rcsB over-expression strains increased. Especially, 10.33 g/L of extracellular polysaccharide was produced by the rcsA over-expression strain, which was five times of that of the wild type strain. On the whole, the regulation of rcsA and rcsB expression provides a novel way to influence the performance of K. pneumoniae.