RcsAB is an atypical two-component regulatory system that can regulate exopolysaccharide biosynthesis and is involved in the virulence of K. pneumoniae. The gene galF is well known as a gene involved in the biosynthesis of capsular polysaccharide (CPS). The specific DNA identification sequence for transcriptional regulation of RcsAB was found to be present in the promoter region of galF. This study aimed to detect the function of RcsAB in virulence and in biofilm and CPS formation. In addition, the transcriptional regulation of the galF gene in K. pneumoniae was studied. To determine the function of rcsAB gene, the wild-type K. pneumoniae strain NTUH-K2044 and the rcsAB knockout and complemented strains were used. The results showed decreased virulence, biofilm formation, and CPS levels in the rcsAB knockout strain. Complementation of the knockout by introducing an rcsAB fragment on an expression plasmid partially restored the virulence, biofilm, and CPS functions of the knockout strain. It indicated that the rcsAB genes might affect CPS formation and virulence of K. pneumonia. RT-qPCR, EMSA and DNase I footprinting assays were conducted to identify the transcriptional regulation of galF by RcsAB. RcsAB was seen to bind to the galF promoter-proximal region, and the binding site was further identified to be located from -177 bp to -152 bp upstream of the galF promoter. In conclusion, RcsAB could regulate the transcription of the galF gene positively by binding to the galF promoter DNA directly, and then affects the CPS formation of K. pneumonia.

RcsAB是一种非典型的两组分调节系统，可以调节胞外多糖的生物合成，并参与肺炎克雷伯菌的毒性。galF基因是众所周知的参与荚膜多糖（CPS）生物合成的基因。发现特定的DNA鉴定序列的RcsAB转录调控存在于galF的启动子区。这项研究旨在检测RcsAB在毒力，生物膜和CPS形成中的功能。另外，研究了肺炎克雷伯菌中galF基因的转录调控。为了确定rcsAB基因的功能，即野生型肺炎克雷伯菌使用NTUH-K2044菌株和rcsAB基因敲除和互补菌株。结果显示rcsAB基因敲除菌株的毒力，生物膜形成和CPS水平降低。通过在表达质粒上引入rcsAB片段来完成基因敲除的补充，部分恢复了基因敲除菌株的毒力，生物膜和CPS功能。说明rcsAB基因可能影响肺炎克雷伯菌的CPS形成和毒力。进行了RT-qPCR，EMSA和DNase I足迹测定法，以鉴定RcsAB对galF的转录调控。RcsAB被认为与galF结合启动子附近区域，并进一步鉴定该结合位点位于galF启动子上游-177 bp至-152 bp之间。总之，RcsAB通过直接与galF启动子DNA结合，可以正向调节galF基因的转录，进而影响肺炎克雷伯菌的CPS形成。