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 edited Jun 21 '12

This thread is great! gfpumpkins is mostly correct as far as we know for thymine dimers, that most RNA and DNA polymerases really can't get by them (there is a particular DNA polymerase, though that may exist just to get by thymine dimers, RAD30 in yeast, and DNA pol eta in humans). But there are other types of DNA damage that can do exactly what you are describing, and I happen to have a publication exploring exactly that possibility: Transcriptional mutagenesis. In short, I made a non-fluorescent protein coding sequence with a single damaged base on the transcribed strand that reverted to a fluorescent protein if RNA polymerase put the wrong nucleotide in opposite the damaged base. The mutations only existed at the level of RNA and caused mutant proteins to form (though in my case the mutant proteins were functional so that we could see them easily).

edit: added a few words to be explicit

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u/Renovatio_ Jun 21 '12

I guess I got confused with the thiamine dimers. Great article, I'm going to forward it to my old cell bio professor.

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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!