Using fluorescent microscopy, scientists have discovered that the bacteria responsible for brucellosis can sense light and use the information to control their virulence.  This discovery is a breakthrough after 120 years of conducting research into the disease that causes abortion in livestock as well as fevers in humans.  What is more significant is that researchers have discovered with the aid of fluorescent microscopy that two other bacteria including one specie that attacks plants sense light with the aid of the same type of protein structure.  More interesting is that at least 94 more species have the code in their DNA.
Trevor Swartz, the lead author of the study has been studying these bacteria for quite sometime and no one discovered that these bacteria can actually sense the light.  With fluorescent microscopy, the ubiquity of the structure suggests that light may actually play a very significant role in the bacterial life than previously known.  Inasmuch as the recurrent structure can be paired with various signaling proteins, it provides the organisms with immense versatility in the manner that they utilize the light. Thanks to fluorescent microscopy, scientists have discovered an entirely new family of light receptors in nature
As discovered in the study utilizing fluorescent microscopy, the receptor molecules possess a light sensing region referred to as an LOV domain since it resembles similar units in other proteins capable to sense light, oxygen or voltage.  Utilizing fluorescent microscopy, the structure likewise crops up in a variety of proteins where it employs its light sensing capability to the entire molecule.  This light-sensing structure is quite different from either the light harvesting molecules of photosynthesis of the light-gathering pigments in the human eyes.
A decade earlier, LOV domains were found with the help of fluorescent microscopy in plant molecules known as phototropins.  The molecules allow plants to perform crucial functions like growing toward the light as well as sensing day length.  What puzzles more the scientists is that why should several bacteria possess the same type of equipment.
To extensively study the LOV domain’s light-sensing function in bacteria, the researchers choose four species whose DNA contained genes for the structure after which they were closely examined with the use of fluorescent microscopy. The four species include Brucella melitenses, B. abortus, a well studied plant pathogen known as Pseudomonas syringae and a common bacterium in sea water referred to as Erythrobacter litoralis.  They merged the genes into Escherichia coli which is a lab friendly bacterium.
The bacteria were later grown in a darkened lab.  Their molecular activities were tracked using radioactive tracers and fluorescent microscopy.   What the researchers noted was that when flashed with a strobe light, the LOV domains immediately changed shape by forming a temporary bond in a process likened to the opening of a hinge.  When open, the hinge exposes the rest of the protein as well as activates it.  However when darkness returns, what happens is that the bond breaks and the LOV domain swings close.
The light-receptor protein involves an enzyme known as histidine kinase.  When exposed by activation of the LOV domain, it marks the other molecules using phosphates as tags.  Another component of the signaling system is the response regulator which relays the signals to the other parts of the cell by transferring the phosphate tags to other molecules.  The versatility of the two-component systems is in the variety of molecules accessible to be tagged.
When Brucella is attacked by the host’s immune system, the light received by the LOV domain stimulates the bacterium’s counter-defenses thereby permitting it to reproduce quickly and making it   highly virulent as noted in fluorescent microscopy.  In the dark, Rubella’s division rate lowers by 90 percent.  When the researchers grew experimental Brucella in the light but with the LOV domain disabled, they discovered an identical drop in a division rate.
Gaining enough knowledge on how bacteria respond to light could result to therapeutic advances.