Transcriptional regulation of pilC2 in Neisseria gonorrhoeae: response to oxygen availability and evidence for growth-phase regulation in Escherichia coli.

The type-4 pilus of Neisseria gonorrhoeae is a dominant surface antigen which facilitates adhesion to host target cells, an essential event in gonococcal infection. pilC2 encodes a 110-kDa protein involved in pilus assembly, pilus-mediated adherence to human epithelial cells in culture and natural competence for DNA transformation. Luciferase activity directed from a chromosomal pilC2::luxAB transcriptional fusion was reduced approximately 4-fold when cells were grown anaerobically. We observed a concomitant reduction in gonococcal piliation by electron microscopy and a reduction in the ability to adhere to ME-180 human epithelial cells when bacteria were grown in the absence of oxygen. Furthermore, we present evidence for growth-phase regulation of the gonococcal pilC2 gene in Escherichia coli, and show that all sequences necessary for growth-phase regulation are contained on a 121-bp pilC2 fragment. Expression from the minimal pilC2 fragment fused to lacZ in single-copy in E. coli was induced 2-fold when cells entered stationary phase. Surprisingly, induction does not require rpoS, the gene, which encodes the starvation-induced sigma factor RpoS. In summary, we have demonstrated that pilC2 is both positively and negatively regulated at the level of transcription. This regulation is most probably relevant to physiological conditions within the human host which influence gonococcal infections.