Isolation of Mutants of Bacteria by UV Exposure

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BACKGROUND

When there is a hereditary change in the base sequence of a DNA it is called mutation. Very few mutations are either neutral or beneficial to organisms but usually they cause harm to living beings as that result in loss of very important cellular function. Under normal conditions mutation occurs in bacteria at a rate of 10-7 or 10-8 per base pair during a single replication round. However, in the presence of a mutagen this rate increases highly. The mutagen can be either in form of chemical or in the form of electromagnetic radiation. Then there are two types of electromagnetic radiation that is ionizing radiation and non-ionizing radiation. This ionizing radiation like x-rays or gamma radiation carries enough energy that helps in removal of the electrons from the cell. When these electrons are removed from this molecules, free radicals are formed that posses the capability to damage any other molecules by oxidation. Then the non-iodizing radiations like ultraviolet light, causes mutagenic effect by excitation of the electrons in the DNA molecules. The electromagnetic radiation differs from others based on its wavelength, frequency and other forms of energy. When the wavelength of the radiation comes down the emittance of energy increases. This is the reason why ionizing radiation is more dangerous than non-ionizing radiation.

So, the objective of this test is to isolate the mutants of bacteria by exposing them to ultra violet light.

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REQUIREMENTS

Sample culture

Sterile swab

Nutrient agar plate

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PROCEDURE

At first take the nutrient agar plate and label them as initials, culture, time of exposure and date. Now take the sterile swab and dip it in the sample culture.¹ Now smear the culture evenly all over the nutrient agar plate. Now keeping the plate opened keep the index card that will cover about half portion of the agar plate. Now place this plate under UV light and leave it for required amount of time. At this time, you should expose your eyes or skin to UV directly as it can affect adversely. Now after the time duration, remove the plate from under the UV light and then remove the index card and cover the petri plate. Then incubate this plate for about 24 hours at 37^oC.After incubation observe the plate and count the number of colonies that has grown in the area that was exposed to UV light.²

Now this are the mutants of bacteria that has undergone mutation after being exposed to UV light. Isolate this colonies make pure culture of this isolated colonies for further study.

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CONCLUSION

These isolated mutant bacteria can help a lot in studying the mutagenesis properties.

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REFERENCES

1. Lederberg, J and Lederberg, EM (1952) Replica plating and indirect selection of bacterial mutants. J Bacteriol. 63: 399–406.
   
2. Madigan & Martinko, Brock Biology of Microorganisms, Eleventh Edition, Pearson Prentice Hall, Inc.