Ultraviolet light is a powerful tool against many pathogens. Although ultraviolet light can wipe out several germs, the exact mechanisms for radiation’s damaging action are elusive. In a study published in the September 2019 issue of PNAS, Texas A&M researchers provided the science behind the germicidal action of ultraviolet light.
The team, led by Dr. Peter Rentzepis, reported that ultraviolet radiation creates holes in the microbes’ outer protective sheath by dislodging tryptophan — a molecule that is an important component of the bacteria’s outer covering. These holes provide gateways for ultraviolet radiation to permeate the bacteria and disrupt its DNA, which then stops the microbes from replicating.
For their experiments, the team looked at the fluorescent light emitted by tryptophan molecules in Escherichia coli — better known as E. coli — and Bacillus subtilis bacteria after shining a beam of ultraviolet radiation on them. As expected, they found the fluorescent light emitted by the tryptophan molecules was drastically reduced at the end of radiation, which typically lasted several minutes. Cell-counting measurements indicated that this reduced fluorescence amounted to a 70% reduction in viable bacteria within the first minute. To the team’s surprise, this decreased fluorescent light came after an initial increase immediately after the radiation was turned on.
Rentzepis’ research group’s findings suggest that in bacteria, ultraviolet light might unfold membrane proteins and detach tryptophan molecules. In turn, this may cause an initial increase in the emitted light signal. With tryptophan plucked out of the cell membrane, the space left behind forms gaping holes for the ultraviolet light to enter and damage DNA.
Rentzepis and his team have also developed and patented the technology for a handheld device that can collect emitted light from bacteria during the radiation process.
FEATURED RESEARCHER