A simple and cheap laboratory class is proposed to illustrate the lethal effect of UV radiation on bacteria and
the operation of different DNA repair mechanisms. The class is divided into two sessions, an initial 3-hour
experimental session and a second 2-hour analytical session. The experimental session involves two separate
experiments: one dedicated to illustrating the lethal effect of UV radiation and the protective effect of DNA
photorepair; the second to explore the operation of DNA repair mechanisms that prioritise survival but introduce
mutations. The procedure makes use of a Pseudomonas aeruginosa double auxotroph, which serves to detect
UV-induced back-mutations to prototrophy. The proposed scheme is carried out by undergraduate students of
the Bacterial Physiology and Genetics course, as part of our Biotechnology curriculum. We think that it will
be a valuable tool for microbiology students to increase their understanding of basic genetic concepts.

• A simple laboratory class using a Pseudomonas aeruginosa auxotroph to illustrate UV-mutagenic killing, DNA photorepair and mutagenic DNA repair

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