January 27, 2015

In a paper just published online in mBio, Yun Luo (right), a former postdoc in the lab and now a group leader at Dupont, led a study that provides insight into how Pseudomonas aeruginosa "senses a surface" during the early steps of building a biofilm.  In short, the paper shows that:
1.  Bacterial can apparently "feel" when they are on the surface - shortly after hitting a surface, they turn on a signaling pathway which prepares the microbe to adopt a life in a biofilm.
2.  As part of this pathway, the microbes use there type IV pilus.  Pili have been long known to help microbes attach to a surface (in fact I published that finding as a postdoc ~20 years ago!), but we think they (somehow) also help the microbe to know it has landed.
3.  The surface-sensing system is complex in that it uses two different signaling molecules - cAMP and c-di-GMP.  These are well-studied signaling molecules in bacteria, but what we show here is that bacteria first turn up cAMP levels, which then primers the cells to turn on c-di-GMP levels - c-di-GMP in turn shuts down motility, which is a key thing to do when you want to stick to a surface! That is, you can't move and stick at the same time.
4.  Finally, induction of cAMP requires the PilJ-Chp chemotaxis like cluster, while induction of c-di-GMP requires the surface protein PilY1, the pilus alignment complex, and SadC.

We think these studies are a first key step in understanding how this microbe adapts to a surface lifestyle.  The work was performed in collaboration with Gerard Wong's group at UCLA and Matt Wolfgang's group at UNC.