THE EFFECT OF ENVIRONMENTAL CONDITIONS ON THE REGULATION OF fimB INVOLVED IN TYPE 1 PILUS EXPRESSION

The bacterial species Escherichia coli causes most urinary tract infections. Adherence to bladder cells via thin appendages called pili are important in causing these infections. One variety of pili is type 1 pili that can undergo phase variation, allowing the bacteria to switch between piliated and nonpiliated states. Phase variation involves several genes, which include fimA, that encodes for the major subunits of type 1 pili and two other genes named fimB and fimE. These last two genes encode for the two DNA binding proteins, FimB and FimE, which contribute to expression of fimA and subsequent formation of the pili. The environment may play a role in the expression of these fim genes. To ascertain how the environment may regulate type 1 pilus expression, a fimB::lacZ fusion was generated on a single copy number plasmid. This fusion was created by connecting part of the fimB gene involved in initiating transcription (i.e. the promoter) to a promoterless β-galactosidase gene, lacZ. The amount of β-galactosidase activity will be affected by the activation of the fimB promoter that will in turn lead to more β-galactosidase being expressed and more conversion of the added substrate. As the fimB gene is shut down, less lacZ is expressed so less substrate is broken down and reduced color occurs. The E. coli cells with plasmid-borne fimB::lacZ were assayed under different pH and salt conditions. As salt concentration increased, fimB expression decreased, whereas when pH decreased, fimB expression also decreased. These results suggest that pH and salt found in human urine can affect fimB expression and possibly type 1 pilus expression.