Question

How can bacterial DNA be released from the bacterial cell for biotechnology experiments?

Answer 1

There are several methods of introducing the ligated DNA into recipient cells that is the cell that does not possess it. Recipient cells after making them 'competent to receive, take up DNA present in its surrounding Since DNA is a hydrophilic molecule, it cannot pass through cell membranes. In the condition that bacteria should take up the plasmid, the bacterial cells must first be made 'competent to take up DNA.

Complete answer:
The competence is started and completed by providing the cells with a known concentration of a divalent cation, such as calcium, and this treatment increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
With some surety calcium chloride causes the DNA to precipitate onto the outside of the cells or it may improve DNA binding.
Transformation : Recombinant DNA can be forced into competent cells by incubating the cells with recombinant DNA on ice. This type of cell is then placed briefly at 42°C (heat shock), and then putting them back on ice.
This makes the bacteria capable of taking up the recombinant DNA. This method is transformation i.e., a procedure through which a piece of DNA is introduced into a host bacterium.
So, if a recombinant DNA that possesses genes for resistance to an antibiotic (e.g., ampicillin) is transferred into E.coli cells, the host cells get transferred into ampicillin-resistant cells. If we now put the transformed cells on agar plates containing ampicillin, only transformants will grow, untransformed recipient cells will die.
Since, one is able to select a transformed cell in the presence of ampicillin, the ampicillin-resistance gene in this case is called a selectable marker.
In one more method known as microinjection, recombinant DNA is directly injected into the nucleus of an animal cell.
In another method, that is usually available for plants, cells are given with high-velocity microparticles of gold or tungsten coated with DNA in a method known as biolistics or gene gun.
And the last method uses 'disarmed pathogen' vectors, which when allowed to infect the cell, transfer the recombinant DNA into the host. For example, Ti plasmid of Agrobacterium and Retroviruses.
Electroporation : Short electrical impulses of high field strength are given. These increase the permeability of protoplast membrane by creating transient microscopic pores, thus making entry of DNA molecules into the cells much easier

Note:
PEG or polyethylene glycol is a compound which helps in protoplast fusion and helps foreign DNA to enter the host cell. Direct injection of DNA into skeletal muscle has given a step to the possibility of using genes as vaccines. Due to low level of expression therapeutic benefits for the treatment of genetic disorder could not be derived. This method gave birth to the concept of DNA vaccine or genetic immunisation.