Introductory Microbiology (1+1)

I.Transformation

Transformation

• A naked DNA or cell free DNA incorporated into the recipient cells and brings about genetic recombination is referred as transformation. Most of the bacteria both G+ and G- are easily transformable but only a fragment of DNA can easily be transformed. The ability of an organism to take up the foreign DNA molecule is referred as competence and the organism is said to be competent. The competence of organisms varies among the organisms. Bacillus has 20% competence cells and E. coli and Streptococcus, 100% of cell become competence.
• The gram –ve bacterium, Haemophilus takes only double strand DNA whereas the Streptococcus and Bacillus can take only single strand DNA, while the complementary strand is simultaneously degraded.
• The naked DNA first bound on the surface of the recipient cell with the help of surface proteins. A single strand of DNA is allowed to enter inside the cell. The entered DNA will be moved to chromosomal DNA and genetic recombination takesplace with the help of RecA protein.

Artificial transformation
The molecular biology techniques now used to transfer a naked DNA to recipient cell artificially are;
1) Calcium chloride mediated transformation: The CaCl2 washed recipient cells mixed with DNA allowed a temperature shock (420 C for 40-60 sec.) will allow the naked DNA to get transformed.
2) Gene gun (particle gun): will allow transformation of plant tissues, yeast, algae etc.
3) Electroporation: Transformation takes place by means of electrical pulses.