A two-component regulatory system modulates twitching motility in Dichelobacter nodosus

•A two-component regulatory system, TwmSR, was identified in D. nodosus.•This system has similarity to chemosensory systems in other bacteria.•Analysis of a twmR mutant showed that the TwmSR system modulates twitching motility.•Video microscopy indicated that TwmSR controls the direction of twitching movement.

Dichelobacter nodosus is the essential causative agent of footrot in sheep and type IV fimbriae-mediated twitching motility has been shown to be essential for virulence. We have identified a two-component signal transduction system (TwmSR) that shows similarity to chemosensory systems from other bacteria. Insertional inactivation of the gene encoding the response regulator, TwmR, led to a twitching motility defect, with the mutant having a reduced rate of twitching motility when compared to the wild-type and a mutant complemented with the wild-type twmR gene. The reduced rate of twitching motility was not a consequence of a reduced growth rate or decreased production of surface located fimbriae, but video microscopy indicated that it appeared to result from an overall loss of twitching directionality. These results suggest that a chemotactic response to environmental factors may play an important role in the D. nodosus-mediated disease process.