Modulation of gonococcal piliation by regulatable transcription of pilE

The gonococcal pilus, a member of the type TV family of pill, is composed of numerous monomers of the pilin protein and plays an important role in the initiation of disease by providing the primary attachment of the bacterial cell to human mucosal tissues. Piliation also correlates with efficient DNA transformation. To investigate the relationships between these pilus-related functions, the piliation state, and the availability of pilin, we constructed a derivative of MS11-C9 (Delta pitE1) in which the lacIOP regulatory sequences control pilE transcription. In this strain, MS11-C9.10, the steady-state levels of pilin mRNA and protein directly correlate with the concentration of IPTG (isopropyl-beta -D-thiogalactopyranoside) in the growth medium and can reach near-wild-type levels of expression. Transmission electron microscopy (TEM) demonstrated that the number of pill per cell correlated with the steady-state expression levels: at a low level of transcription, single long pill were observed; at a moderate expression level, many singular and bundled pill were expressed; and upon full gene expression, increased lateral association between pill was observed. Analysis of pilus assembly by TEM and epithelial cell adherence over a time course of induction demonstrated that pill were expressed as early as 1 h postinduction. Analysis at different steady-state levels of transcription demonstrated that DNA transformation efficiency and adherence of MS11-C9.10 to transformed and primary epithetial cells also correlated with the level of piliation, These data show that modulation of the level of pilE transcription, without a change in pilE sequence, can alter the number of pill expressed per cell, pilus bundling, DNA transformation competence, and epithelial cell adherence of the gonococcus.