How bacteria recognise and respond to surface contact

Bacterial biofilms can cause medical problems and issues in technical systems. While a large body of knowledge exists on the phenotypes of planktonic and of sessile cells in mature biofilms, our understanding of what happens when bacteria change from the planktonic to the sessile state is still very incomplete. Fundamental questions are unanswered: for instance, how do bacteria sense that they are in contact with a surface, and what are the very initial cellular responses to surface contact. Here, we review the current knowledge on the signals that bacteria could perceive once they attach to a surface, the signal transduction systems that could be involved in sensing the surface contact and the cellular responses that are triggered as a consequence to surface contact ultimately leading to biofilm formation. Finally, as the main obstacle in investigating the initial responses to surface contact has been the difficulty to experimentally study the dynamic response of single cells upon surface attachment, we also review recent experimental approaches that could be employed to study bacterial surface sensing, which ultimately could lead to an improved understanding of how biofilm formation could be prevented

Reassessing the role of the Escherichia coli CpxAR system in sensing surface contact

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, specifically to 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 should be reconsidered

Manipulating rod-shaped bacteria with optical tweezers

Optical tweezers have great potential in microbiology for holding and manipulating single cells under a microscope. However, the methodology to use optical tweezers for live cell studies is still at its infancy. In this work, we determined suitable parameters for stable trapping of single Escherichia coli bacteria, and identified the upper limits of IR-exposure that can be applied without affecting viability. We found that the maximum tolerable IR-exposure is 2.5-fold higher when employing oscillating instead of stationary optical trapping (20 J and 8 J, respectively). We found that good stability of cells in an oscillating trap is achieved when the effective trap length is 20% larger than the cell length, the oscillation frequency higher than 100 Hz and the trap oriented perpendicular to the medium flow direction. Further, we show, using an IR power just sufficient for stable holding, that bacteria remain viable during at least 30 min of holding in an oscillating trap. In this work, we established a method for long-term stable handling of single E. coli cells using optical tweezers. This work will pave the way for future use of optical tweezers in microbiology