In a Davis Utube experiment you add a different strain of au

In a Davis U-tube experiment, you add a different strain of auxotrophic bacteria to each side of the apparatus. After allowing time for growth, you transferred and grew the bacteria on a plate with minimal medium and noticed the growth of prototrophs. By which process did this genetic transfer possibly occur if... There was DNase enzyme (breaks down free-floating DNA) present in the medium? There was no DNase enzyme in the medium? There was DNase enzyme present in the medium and the sintered glass filter was removed from the U-tube apparatus (no separation between bacterial strains)? Answer the following questions with F^+, F^-, or Hfr. More than one of these three may apply to a single question. Bacterium that does not have an F factor. Bacterium that can donate an F factor.

Solution

Answer:

4. For DNA transfer to take place through conjugation between the two different bacteria, physical contact is necessary.

a. When DNase is present, it can cleave any naked DNA present in the media. So, the only way that can transfer DNA from one bacterial auxotroph to the other is through transduction (if the media is contaminated with a bacteriophage) or through physical contact, i.e, conjugation (if the sintered glass filter is defective).

b. When there is no DNase, the most probable mechanism of gene transfer is transformation (transfer of naked DNA).

c. In this case, there can be physical contact between the two auxotroph strains. So, gene transfer probably took place through conjugation.

5. a. Bacteria that does not have a F factor: F^-

b. Bacteria that can donate a F factor: F⁺

( Hfr strains cannot transfer the F-factor efficiently to the F- strain due to the short duration of conjugation tube formation)