Re: Infrared affects on microorganism

Osbert Cheung,

I’m not sure that the answer to your question is really known (at least I couldn’t find any information concerning the effects of infrared radiation on microorganisms). However, I thought I would explain a little bit about the effects and uses of electric pulses on bacteria. In addition, I will give a brief explanation of the effects of ultraviolet light (electromagnetic radiation).

Electric pulses are now commonly used in the laboratory to "inject" foreign DNA into pre-treated bacteria for purposes of expressing large amounts of a particular piece of DNA (the DNA is usually in plasmid, or circular form). This process is called electroporation. The pre-treated bacteria are referred to as being "electroporation competent" and they are made competent through a series of cold washes in glycerol based buffers. Basically, a small amount of competent bacteria is placed in a special cuvette with a small aliquot of the DNA that you want inside the bacteria. Then the mixture is pulsed with a few mV of electricity, which disrupts the cell membrane and allows for uptake of the DNA. Because of the pre-treatment, the cells do not die.

However, bacteria and yeast are normally sensitive to electric fields. According to Hulsheger, et. al. (1983), treatment with high electric pulses gave survival rates of less than 1% for all microorganisms tested. They conclude that electric fields induce selective damage to inner cell membranes. For more information on their findings, look up the following paper:

Hulsheger H, Potel J, Niemann EG, (1983) "Electric field effects on bacteria and yeast cells" Radiat Environ Biophys 22 (2): 142-162.

Electromagnetic radiation can also kill bacteria, or any cell for that matter. Specifically, ultraviolet light (UV) promotes mismatched base pairing and cleavage of DNA as well as various types of protein modifications. That means when a cell is exposed to enough UV light, their DNA is damaged (which usually leads to mutations that ultimately kill the cell) and the cellular proteins are damaged and are unable to function properly. A good example of this is a sunburn. The UV light from the sun damages the outer layers of epithelial cells, causing those cells to die and flake off (which is why our skin peals after a sunburn). The same principal applies to bacteria, except they don’t have a thick layer of cells to protect them from the damaging effects of UV light, so they die.

To my knowledge, the effects of infrared light (IR) on microorganisms are either not known, or IR doesn’t adversely effect cells. At least, I couldn’t find any specific information on it. I will take an educated guess and say that IR probably doesn’t have the same effects on bacteria that UV does. The reason is that both DNA and proteins have aromatic groups that absorb light (and thus energy) in the ultraviolet range, but not in the IR range. In fact, this property is commonly used in the laboratory to quantify amounts of DNA or protein in a sample. It can even be used to see if a protein sample is contaminated with DNA (or visa versa) by taking advantage of the fact that proteins tend to absorb UV light at around 280 nanometers, whereas DNA absorbs at around 260 nanometers.

I hope this fully addresses your question. If you want further information, I would be glad to help you out!

Thanks for the great question!

Brian Cobb