Question

Describe how bacterial DNA transfer from one cell to the others.

Answer 1

Generally bacteria undergo asexual reproduction via fission. However, certain types of DNA uptake and transfer mechanisms do exist in bacteria too -

Transformation is the uptake of foreign DA by a bacterium from the surrounding medium.

A form of sexula reproduction called conjugation does occur in bacteria. This, involves the transfer of DNA from a donor bacterium to a recepient bacterium. this involves the use of certain types of plasmids which can be transferred from one bacterial cell to another.

An example is the F plasmid. The bacteria possessing this plasmid is called F⁺ (donor cell) while the bacteria which does not harbour this plasmid is called a F^- (recepient) cell. F plasmid is a self transissible plasmid which can mediate its own tranfer. It bears tra genes which aid in transfer. It also encodes for an F pillus which makes contact with the F^- bacteria. Upon contact, a conjugation tube is made which brings the two bacterial cell into close proximity. A mating bridge forms which enables DNA transfer.

Often, the F plasmid can get integrated into the bacterial chromosme forming Hfr (High Frequency recombinants) strain. These can still conjugate with F^- cells. When an Hfr strain transfers the F plasmid the chromosomal DNA is also tranferred alongwith. The transfer is although not complete and so only a portion of the F plasmid and some portion of the chromosomal DNA is transferred.

The resulting strain is called F'. It cannot conjugate. These cells are merodiploids i.e. these cells are diploid dor some genes which were transferred alongwith the F plasmid.

The chromosomal DNA in F' cells can also recombine with the chromosmal DNA of recepiet cell.