What Was Transformed in Griffith's Experiment?

The genetic information of the bacteria used was transformed in Griffith’s experiment. Transformation involves the alteration of the genetic information of a cell through the direct uptake and expression of DNA from its surroundings.

The experiment was conducted in 1928 by English medical officer and geneticist Frederick Griffith. It was one of the first experiments to demonstrate the transformative capabilities of microorganisms.

Using two strains of pneumococcus bacteria, Griffith infected two isolated test populations of mice. One of the strains featured a smooth polysaccharide coating that shielded it from the host’s immune system, enabling infection. The other strain did not have this coating. The coated bacteria were killed through heating, and their remains were mixed with the culture of the noncoated bacteria. Neither strain was able to independently kill the mice, but the mixture of the live and dead strains did kill the mice. Furthermore, the blood of the deceased mice yielded live samples of both strains. The noncoated bacteria was able to copy the genetic data of the coated dead bacteria, enabling the former to transform into the latter.

Conjugation and transduction are two means other than transformation in which outside genetic information can be integrated into a bacterial cell.