Griffith's Transformation Experiment

Pneumococcus bacteria include two strains, a virulent S strain with a Smooth glycoprotein coat that kills mice (left), and a non-virulent R  Rough strain that does not (middle). Heating destroys the virulence of S (right).

In the critical experiment, Frederick Griffith (1928) mixed heat-killed S with live R and injected the combination into mice: the mouse died.The dead mouse's tissues were found to contain live bacteria with smooth coats like S. These bacteria were subsequently able to kill other mice, and continued to do so after several generations in culture.

Griffith concluded that something in the heat-killed S bacteria 'transformed'  the hereditary properties of the R bacteria. The nature of this 'transforming principle' was unknown.

HOMEWORK. What do each of the "Control" experiments control for? Suppose the combination of heat-killed S and live R killed the first generation of mice, but not the second or subsequent generations. What would you conclude about transformation?

All text material ©2022 by Steven M. Carr