Switching quorum sensing on and off with light

Artificial hips, prosthetic knees, new disks in the spine. The surfaces of these commonly used implants are all susceptible to colonization by bacteria that form hardy biofilms, and these infections can be a major reason why the implants fail.

Preventing these failures is one of the reasons Ben Feringa and his team at the University of Groningen are interested in disrupting quorum sensing (QS)—the communication between bacteria. “This is a serious issue,” Feringa says. “So if we can find ways to collaborate and help doctors in the clinic a little bit, I would be very pleased.”

By adding an azobenzene photoswitch to a QS molecule, the team has managed to create a light-controlled on-off switch for bacterial communication and organization (Chem 2019, DOI: 10.1016/j.chempr.2019.03.005).

“This is a great paper that demonstrates the usefulness of photopharmacology to control bacterial communities,” says Dirk Trauner at New York University, who is one of the pioneers of photopharmacology, or light-activated drugs and treatments.

QS processes kick in when bacteria increase in number and need to change their behavior to survive. As the number of bacteria increases, so do the levels of QS molecules. Once this chemical chatter reaches a critical level, the cellular pathways activated by those molecules allow bacteria to act as a group.

Feringa’s team made compounds based on a QS molecule from the bacteria Pseudomonas aeruginosa. One of the photoswitching compounds, AHL5, converts between two isomers that activate and inactivate QS pathways with a 700-fold difference in activity when tested in cultures of P. aeruginosaand Escherichia coli.

Feringa admits that AHL5 can’t yet be used in a clinical setting. For example, AHL5 switches between its trans and cis forms with ultraviolet light, which is not clinically useful because it doesn’t penetrate deeply into tissue. Red light would be a better way to trigger these molecules, he says. Feringa points out that as well as medical treatments, being able to control bacterial communication with light could also help study the molecular biology behind bacterial behavior.