GadE regulates fliC gene transcription and motility in Escherichia coli

Escherichia coli (E. coli) express flagella to ascend human urinary tracts. To survive in the acidic pH of human urine, E. coli uses the glutamate decarboxylase acid response system, which is regulated by the GadE protein.

To determine if growth in an acidic pH environment affected fliC transcription and whether GadE regulated that transcription.

A fliC-lacZ reporter fusion was created on a single copy number plasmid to assess the effects of acidic pH on fliC transcription. Further, a ΔgadE mutant strain of a uropathogenic E. coli was created and tested for motility compared to the wild-type strain.

Escherichia coli cells carrying the fliC-lacZ fusion displayed significantly less fliC transcription when grown in an acidic pH medium compared to when grown in a neutral pH medium. Transcription of fliC fell further when the E. coli was grown in an acidic pH/high osmolarity environment. Since GadE is a critical regulator of one acid response system, fliC transcription was tested in a gadE mutant strain grown under acidic conditions. Expression of fliC was derepressed in the E. coli gadE mutant strain grown under acidic conditions compared to that in wild-type bacteria under the same conditions. Furthermore, a gadE mutation in a uropathogenic E. coli background exhibited significantly greater motility than the wild-type strain following growth in an acidic medium.

Together, our results suggest that GadE may down-regulate fliC transcription and motility in E. coli grown under acidic conditions.