An international group of investigators, led by Trevor E. Swartz from the Department of Chemistry and Biochemistry at University of California, Santa Cruz, has made an interesting discovery. It seems that Brucella melitensis and related bacterial species rely on light-sensory enzymes–blue-light-dependent histidine kinases– to upregulate their virulence. Brucella is, of course, a well known aggressive pathogen in humans and some animals.
From the National Science Foundation statement:
Brucellosis bacteria “have been very well studied for years, and no one knew they could sense light,” said Trevor Swartz of the University of California, Santa Cruz, the study’s lead author. “And now it seems like it’s a common thing rather than being an anomaly…”
The scientists found that bacterial sensors are closely related to phototropins– the light receptors that detect blue light and direct plants to grow towards light sources. “The central message is that many bacteria have signaling proteins that contain the same light-absorbing domain as those found in the higher plants,” says Winslow Briggs of the Carnegie Institution, who was a member of the research team. “One of these is a vicious pathogen called Brucella. A species of Brucella is a serious pathogen of cattle that causes abortions of calves, and another species is a nasty pathogen of humans.”
The researchers are unsure of how the regulation of virulence by light benefits Brucella. But they suspect that it somehow helps the bacteria overcome the human or animal host’s disease-fighting defenses and enables it to reproduce rapidly. They also suspect that light signals the bacteria when it is outside of a host, such as an infected, aborted cow fetus lying in a field. Under such circumstances, increased virulence would help the bacteria survive and infect a new host.
Like plant phototropins, the bacterial sensors have a protein sequence called a LOV (pronounced “love”) protein domain, so named because it detects light and resembles some molecular packages that detect oxygen or voltage…
The study in the August 24 issue of Science confirms the light-sensing function of the LOV domain proteins in four bacteria species. But the ubiquity of the light structures in bacteria species suggests that light may play a much more important role in bacterial life and virulence than previously believed.
More from the NSF…
A comment from the Science…
Abstract: Blue-Light-Activated Histidine Kinases: Two-Component Sensors in Bacteria