Multiple Copies of flhDC in Paraburkholderia unamae Regulate Flagellar Gene Expression, Motility, and Biofilm Formation

Hexameric structure of the flagellar master regulator FlhDC from Cupriavidus necator and its interaction with flagellar promoter DNA

Bacterial flagella are assembled with ∼30 different proteins in a defined order via diverse regulatory systems. In gram-negative bacteria from the Gammaproteobacteria and Betaproteobacteria classes, the transcription of flagellar genes is strictly controlled by the master regulator FlhDC. In Gammaproteobacteria species, the FlhDC complex has been shown to activate flagellar expression by directly interacting with the promoter region in flagellar genes. To obtain the DNA-binding mechanism of FlhDC and determine the conserved and distinct structural features of Betaproteobacteria and Gammaproteobacteria FlhDCs that are necessary for their functions, we determined the crystal structure of Betaproteobacteria Cupriavidus necator FlhDC (cnFlhDC) and biochemically analyzed its DNA-binding capacity. cnFlhDC specifically recognized the promoter DNA of the class II flagellar genes flgB and flhB. cnFlhDC adopts a ring-like heterohexameric structure (cnFlhD₄C₂) and harbors two Zn-Cys clusters, as observed for Gammaproteobacteria Escherichia coli FlhDC (ecFlhDC). The cnFlhDC structure exhibits positively charged surfaces across two FlhDC subunits as a putative DNA-binding site. Noticeably, the positive patch of cnFlhDC is continuous, in contrast to the separated patches of ecFlhDC. Moreover, the ternary intersection of cnFlhD₄C₂ behind the Zn-Cys cluster forms a unique protruding neutral structure, which is replaced with a charged cavity in the ecFlhDC structure.

Polysaccharides from Vaccaria segetalis seeds reduce urinary tract infections by inhibiting the adhesion and invasion abilities of uropathogenic Escherichia coli

The seeds of Vaccaria segetalis (Neck.) are from a traditional medicinal plant Garcke, also called Wang-Bu-Liu-Xing in China. According to the Chinese Pharmacopoeia, the seeds of V. segetalis can be used for treating urinary system diseases. This study was designed to investigate the underlying mechanism of VSP (polysaccharides from Vaccaria segetalis) against urinary tract infections caused by uropathogenic Escherichia coli (UPEC). Here, both in vitro and in vivo infection models were established with the UPEC strain CFT073. Bacterial adhesion and invasion into bladder epithelial cells were analyzed. We found that VSP reduced the adhesion of UPEC to the host by inhibiting the expression of bacterial hair follicle adhesion genes. VSP also reduced the invasion of UPEC by regulating the uroplakins and Toll-like receptors of host epithelial cells. In addition, the swarming motility and flagella-mediated motility genes flhC, flhD and Flic of UPEC were diminished after VSP intervention. Taken together, our findings reveal a possible mechanism by which VSP interferes with the adhesion and invasion of UPEC.