Abstract
For proper biofilm formation, bacteria must have mechanisms in place to sense adhesion to surfaces. In Escherichia coli, the CpxAR and RcsCDB systems have been reported to sense surfaces. The CpxAR system is widely considered to be responsible for sensing attachment, to specifically hydrophobic surfaces. Here, using both single-cell and population-level analyses, we confirm RcsCDB activation upon surface contact, but find that the CpxAR system is not activated, in contrast to what had earlier been reported. Thus, the role of CpxAR in surface sensing and initiation of biofilm formation needs to be reconsidered.
Significance statement E. coli is capable of forming medically problematic biofilms, which are surface-associated microbial communities, protected by an exopolymeric matrix and with increased antibiotic tolerance. How these bacteria sense physical contact with a surface, which may lead to initiation of the biofilm formation process, is largely elusive. The signal transduction systems CpxAR and RcsCDB have previously been found to activate upon surface contact. Here, we confirm that RcsCDB is a surface sensing system, immediately responding to attachment. In contrast, using two different experimental approaches, we found that the CpxAR system does not perceive surface contact. Thus, contrary to the current view, the CpxAR system does not play a signaling role in the first step of biofilm initiation.
