Fundamentals of Microbiology

3.4.3.1 Transformation

A cell that is able to take up a molecule of DNA and be transferred is called competent cell. Bacteria differ in the form in which DNA is taken up. In Gram negative bacteria (eg. Haemophilus) only DS DNA is taken up into the cell, however only SS – DNA segment is incorporated into the genome. In Gram positive bacteria (Streptococcus sp. and Bacillus) only SS – DNA is taken up. Transforming DNA is bound at the cell surface by DNA binding protein, after which either double stranded DNA is taken up or nuclease degrades one strand and the other is taken up. After uptake, the DNA is attached to Rec A protein and gets integrated into the genome.