UV (ultraviolet) radiation kills bacteria by damaging the bacterial DNA. Specifically, the UV radiation causes thymine dimers to form within the DNA molecule. Thymine dimers are when two thymine bases become bound together in a chemical bond, leading to a distortion of the DNA helix. This distortion can inhibit normal DNA replication and transcription, ultimately leading to cell death or inactivation of the bacteria.
In addition to damaging DNA, UV radiation can also damage the cell membrane and other cellular components, further contributing to bacterial death. However, it's important to note that not all bacteria are equally susceptible to UV radiation. Some bacteria have developed mechanisms to repair or prevent thymine dimers from forming, making them more resistant to UV damage.