Effect of UV Radiation on Bacterial Growth

Mutations are a heritable change in the base sequence of DNA. Such mutations can be neutral or beneficial to an organism, but most are actually harmful because the mutation will often result in the loss of an important cellular function. Mutagens can be in the form of a chemical (nicotine) or in the form of electromagnetic radiation. Again there are two forms of electromagnetic radiation that are mutagenic; ionising radiation and non ionising radiation. Ionising radiation (x-ray, gamma radiation) has the potential to remove electrons from molecules in a cell. These electrons called free radicals which damage most other molecules in a cell, such as DNA or RNA, by oxidising them. Non ionising radiation (UV) causes formation of pyrimidine dimers in the DNA molecule i.e. adjacent pyrimidine units are ionised forming highly reactive free radicals. These ionised pyrimidines interlink to form the dimers. The dimerisation occurs by the formation of cyclobutane ring and this ring inhibits the replication process, thus hindering the normal functioning of the cell.  

 When UV light hits a DNA, it is absorbed by the purine and pyrimidine molecules in the chain. This affects the normal base pairing of the DNA, and single-strand breaks will happen in the pairing of the DNA. Furthermore, the UV light destroys harmful microbes such as bacteria, yeast, moulds, viruses and algae.

  Experimently proved , bacteria mortality was approximately 40-75% for Serratia marcescens exposed to ultraviolet light (at 254 nm) for 15 seconds and about 75-90% bacteria mortality for the 30 second exposure. One minute of exposure time to ultraviolet light resulted in 95-99% bacteria mortality.