In vitro analysis of OmpR regulation of the fimB and fimE genes of Uropathogenic Escherichia coli

Abstract

Uropathogenic Escherichia coli (UPEC) cause more than 90% of all human urinary tract infections (UTIs). Type 1 pili on the surface of UPEC allow the cells to adhere to and invade bladder epithelial cells. The fimB and fimE genes encode site-specific recombinases that position an invertible element containing the promoter for the gene of the main structural subunit of the type 1 pili. To sustain a UTI, UPEC must be able to respond to changes in environmental pH and osmolality. The EnvZ/OmpR two-component regulatory system is involved in osmoregulation in E. coli. To ascertain if OmpR directly bound to fimB or fimE gene promoters, DNase I footprinting was performed using OmpR or phosphorylated OmpR (OmpR-P) mixed with the fimB and fimE promoter regions of UPEC NU149. Both OmpR-P and OmpR bound weakly to one fimB promoter. However, neither OmpR nor OmpR-P bound to the fimE promoter region. Because there was weak binding to one fimB promoter, strain NU149 was grown in different pH and osmolality environments, total RNAs were extracted from each population, and converted to cDNAs. Real-time reverse transcriptase PCR showed no differences in ompR transcription among the different growth conditions. Conversely, Western blots showed a significant increase in OmpR protein when the UPEC were grown in a combined acidic pH/high osmolality environment versus a neutral pH/high osmolality environment. Together these results suggest that OmpR may be post-transcriptionally regulated in UPEC grown in an acidic pH/high osmolality environment which may affect fimB regulation in UPEC.