An auxotrophic strain of the bacterium E. coli can only grow on a minimal medium

Question

An auxotrophic strain of the bacterium E. coli can only grow on a minimal medium containing thymine (Strain A) and will not grow on unsupplemented minimal medium. Another auxotrophic strain can only grow on a minimal medium containing leucine (Strain B) and will not grow on unsupplemented minimal medium. Devise an experiment to test whether DNA from Strain A could transform Strain B. A transformed strain would be prototrophic and able to grow on minimal medium without supplements. Be certain to explain your hypothesis, to devise a control, to clearly state the experiment, to indicate what results would confirm your hypothesis and what results would refute your hypothesis.

Explanation / Answer

In this design and experiment where auxotrph B will grow on a media that contain leucine but this strain is not auxotrphic for thymine, hence, this strain can provide the thymine synthesizing gene to auxotroph A strain. In continuation of this process we grow and isolate the genomic DNA of strain B and transform it into the strain A.

Here we can use cells A + DNA isolating buffer can be use as control and cell will spread on minimal media and media that contain thymine

In second control strain A cells + DNA that is digested with DNase enzyme will transformed in strain A and will grow in the minimal media and media that contains thymine.

In third experiment strain A cells will be digested with the DNA of strain B and will plate on thymine containing media as well as minimal media.

Here thymine media will indicate that cells are working and alive.

DNA treated with DNase will show that due to absence of DNA that cell is unable to convert it into protrophs.

Last experiment show that it DNA is responsible to grow the cells on minimal media.

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