Suggest a change that can be made to the experiment in question 1 that would red

Question

Suggest a change that can be made to the experiment in question 1 that would reduce the 50-fold increase in gal - mutants grown in irradiated host cells? (Question 1 =

Various colorimetric indicators have been developed that allow one to easily distinguish between gal + and gal –. These can be used, for example, to measure mutagenesis rates of a gal + specialized transducing phage that carries the gal genes. e.g., Tetrazolium in the appropriate media will cause gal + to make a red plaque on an appropriate E. coli host, compared to a colorless plaque for gal-. To measure mutagenesis rates of the E. coli host bacteria, there are many assays that can easily be applied (e.g., the rate of colonies that appear that are resistant to an antibiotic.).

An E. coli culture is lightly irradiated with UV light such that ~98% of the cells are still able to make colonies. Among the survivors, we find that the rate of mutation to antibiotic resistance has increased 50-fold relative to an un-irradiated culture. Interestingly, if we grow (un-irradiated) gal + on the irradiated and un-irradiated cells, the rate of gal – plaques is also increased 50-fold by the irradiated host even though the phage saw no damaging UV!)

Explanation / Answer

Basically, the lambda phage has taken up the gene while infecting irradiated cells and hence helps in gene transduction. Hence, the cells (both radiated and irradiated) should not be grown together where the phage may transfer the mutated gene from irradiated to un-irradiated cells and confer resistance to them.

"A malaria biologist"

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