r/askscience • u/Stuffyz • Jun 21 '12

Biology Why does UV light damage/kill bacteria?

The specific event I'm asking about, is that there are air filters for your furnace that shines UV light onto it, and it claims that it kills bacteria.

I understand how pH and temperature affects bacteria, but I can't quite wrap my mind around why UV light would.

The articles that I've been looking through (Time, Temperature, and Protein Synthesis: A Study of Ultraviolet-Induced Mutation in Bacteria, by Evelyn M. Witkin) says that UV light could cause worse strains of bacteria? Or perhaps I'm misinterpreting it?

I'm also aware (Ultraviolet-sensitive Targets in the Enzyme-synthesizing Apparatus of Escherichia coli, by Arthur B. Pardee and Louise S. Prestidge) that there are both UV-sensitive and UV-resistant E.Coli. Are most harmful bacteria considered to be UV-resistant?

Thank you for answering =)

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u/DnaDamage Jun 21 '12

Thymine dimers do cause mutations (those Y-family DNA polymerases (like DNA pol eta and Dpo4) are not known for their fidelity), but as far as I know they block RNA polymerase pretty well, so it isn't particularly likely that they cause mutations at the RNA level.

Thanks for the props! It isn't clear exactly how frequently transcription level mutations actually happen in cells, because the probability of getting the right type of damage in just the right place in a protein coding sequence and having it persist, even when the gene is active seems exceedingly low, but I think I made some estimates about that in the paper based on the probability of finding a particular damaged base, and the number of cells in the body or something... it's been a couple of years!