The Effect of UV Light on Bacteria Growth

UV light is often used in tanning parlors and salons.

UV light is electromagnetic radiation with wavelengths in the 400 to 10 nanometer range. Ultraviolet light photons have much higher energies than photons of visible light and thus can damage DNA in bacteria and other organisms.

Function

Photons of UV light have sufficient energy to break some chemical bonds. The most common kind of DNA damage in bacteria under UV light is a pyrimidine dimer, where two adjacent bases in the bacterium's DNA become cross-linked. The UV light can also create double-strand breaks in the DNA.

Effects

If they are not repaired, pyrimidine dimers distort the structure of the DNA molecule and prevent DNA replication during cell division, which can cause cell death. Bacteria can circumvent pyrimidine dimers using the so-called SOS system, although this system makes numerous mistakes, leading to an increased rate of mutation. If they are not repaired, double-strand breaks can also lead to mutations or cell death.

Considerations

UV light kills bacteria by inducing so much DNA damage that the bacteria cannot cope. It does not kill spores, however, so it will not necessarily sterilize surfaces. The UV light will only be effective if a sufficient dose is administered. Generally, bacteria are most sensitive to UV light with a wavelength in the 240 to 300 nanometer range.

References

• Bard College: Effect of Ultraviolet Radiation on Bacteria
• MadScience: How Does UV Light Mutate Bacteria?
• "Genetics: A Conceptual Approach"; Benjamin A. Pierce; 2006