克雷白氏肺炎桿菌CG43中MrkH、 MrkI、MrkJ和CsgD在調控第一型與第三型線毛表現所扮演的角色

Abstract

Klebsiella pneumoniae type 1 and type 3 fimbriae have been reported to be important virulence factors. Analysis of the Klebsiella pneumoniae CG43 genome revealed the two fimbriae encoding gene clusters are physically linked, which suggesting a coordinated -regulation for their expression. In the study, regulatory roles of the MrkH, MrkI, and MrkJ and CsgD on the expression of the two fimbriae were investigated. Firstly, the K. pneumoniae CG43S3-derived mutants respectively with a gene-deletion of mrkH, mrkI, mrkJ, and csgD were generated. The deleting effects on the fimbrial activities were then determined using analysis of mannose-sensitive yeast agglutination, western blot hybridization, and biofilm formation. An increased expression of type 1 fimbriae and a decreased expression of type 3 fimbriae were found for the mrkI strain. The deletion of mrkH also decreased the expression of MrkA and biofilm formation activity but had no apparent effect on FimA expression. On the other hand, the mrkJ deletion appeared to slightly increase the MrkA expression but decrease the biofilm formation activity while the csgD deletion reduced the promoter activity of MrkA. The mrkI deletion reduced the mrkA promoter activity but increased OFF-to-ON inversion of the fimS suggesting MrkI is the transcription regulator for their reciprocal expression. Moreover, a phosphodiesterase activity of the recombinant MrkJ was demonstrated implying the second messenger c-di-GMP (bis-(3′-5′)-cyclic dimeric GMP) plays a regulatory role on the expression of type 3 fimbriae. The possibility was further supported by the notion that overexpression of the c-di-GMP binding protein MrkH apparently increased the type 3 fimbriae activity.