Transcriptional regulation of the yersiniabactin receptor fyuA gene by the ferric uptake regulator in Klebsiella pneumoniae NTUH-K2044.

The ferric uptake regulator (Fur) is a global regulator that influences the expression of virulence genes in Klebsiella pneumoniae. Bioinformatics analysis suggests Fur may involve in iron acquisition via the identified regulatory box upstream of the yersiniabactin receptor gene fyuA. To observe the impact of the gene fyuA on the virulence of K. pneumoniae, the gene fyuA knockout strain and complementation strain were constructed and then conducted a series of phenotypic experiments including chrome azurol S (CAS) detection, crystal violet staining, and wax moth virulence experiment. To examine the regulatory relationship between Fur and the gene fyuA, green fluorescent protein (GFP) reporter gene fusion assay, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR), gel migration assay (EMSA), and DNase I footprinting assay were used to clarify the regulatory mechanism of Fur on fyuA. CAS detection revealed that the gene fyuA could affect the generation of iron carriers in K. pneumoniae. Crystal violet staining experiment showed that fyuA could positively influence biofilm formation. Wax moth virulence experiment indicated that the deletion of the fyuA could weaken bacterial virulence. GFP reporter gene fusion experiment and RT-qPCR analysis revealed that Fur negatively regulated the expression of fyuA in iron-sufficient environment. EMSA experiment demonstrated that Fur could directly bind to the promoter region of fyuA, and DNase I footprinting assay further identified the specific binding site sequences. The study showed that Fur negatively regulated the transcriptional expression of fyuA by binding to upstream of the gene promoter region, and then affected the virulence of K. pneumoniae.