Surface sensing in Escherichia coli

Adhesion of the bacterium Escherichia coli to a surface can lead to initiation of biofilm formation, which is a medically relevant process. However, little is known about how adhesion is perceived and which surface sensing systems are involved. In this thesis, we have studied several potential surface sensing systems in E. coli and we found that only the RcsCDB phosphorelay is responsive to surface contact. This system was rapidly activated in surface-attached cells under specific conditions and our results suggest that Rcs could trigger a metabolic adaptation that enables cells to cope with nutrient limitation, as commonly encountered in developing biofilms. Furthermore, our findings show that the CpxAR two-component system, which is widely considered to be a surface sensing system, is in fact not responsive to surface contact. While studying the Cpx system, we found that it is instead highly responsive to a chemical signal, i.e. the presence of copper ions, and that cells condition their medium during growth, which protects them against toxic concentrations of copper. Finally, to facilitate further research in the field of surface sensing, we established the possibilities and limits of optical tweezers for manipulation of single bacteria under the microscope. Using an oscillating optical trap, we were able to hold individual E. coli cells for at least 30 minutes without affecting viability