Transformation

Transformation- it is the natural process, through which bacterial population transfer the genetic material to acquire phenotypic features. The event of transformation was first time demonstrated by Frederick Griffith in 1928. The schematic presentation of the experiment is given in Figure 38.1. Griffith has used two different Streptococcus pneumonia strains, virulent (S, causes disease and death of mice) and avirulent (R, incapable of causing disease or death of mice). In a simple experiment he injected 4 different combination of bacterial mixture, (1) live S, (2) heat killed S, (3) live R, (4) mixture of live R and heat killed S in to the mice. The observation indicates that live S has killed the mice where as mice were healthy with heat killed S or live R. Surprisingly, mice injected with mixture of live R with heat killed S were found dead, and bacteria isolated from these dead mice were virulent. Based on these observations, Griffith hypothesized the existence of a transforming agent (Protein, DNA) being transferred from heat killed virulent strain to the avirulent strain and proposed the concept of transformation. Later, Oswald has proved that the transforming factor is DNA rather than protein. 

Figure 38.1: Discovery of Transformation

Lab Experiment 38.1 : Transformation PET23a into the E.coli and calculate transformation efficiency.
Background Information: Transformation is the process by which cell free DNA is taken up by another bacteria. The principle steps of transformation are given in Figure 38.2.The DNA from donor bacteria binds to the competent recipient cell and DNA enters into the cell. The DNA enters into the recipient cell through a uncharacterized mechanism. The DNA is integrated into the chromosomal DNA through a homologous recombination. Naturally transformation is common between closely related species only.