Griffin performed experiments demonstrating that when live, nonpathogenic S. pneumoniae (which produce rough-surfaced colonies) are mixed with killed smooth-surfaced S. pneumoniae (which are pathogenic when alive) and are then injected into mice, the mice become ill. Bacteria isolated from these sick mice form smooth colonies characteristic of the pathogenic strain.

What happened to the bacteria to make them pathogenic to the mice?

The experiment of Griffith on S. pneumoniae leads to the conclusion that the bacteria can take the DNA from the surrounding environment by the process of "Transformation".

He selected the two strains of bacteria, the smooth pathogenic strains (S strains) and the rough non-pathogenic strain (R strains). When he injected the dead S bacteria and live R bacteria, he obtained the live S bacteria from the mice.

He was amazed at how the dead S strain bacteria became alive and concluded that the dead S strain bacteria were transformed into the live S strain bacteria and named the process transformation.
The transformation process refers to the uptake of the DNA material from the surrounding environment.

Thus, transformation is the correct answer.

Qwletter Qwletter · Answer 2 · 2023-09-04T10:38:01-04:00

Final answer:

Frederick Griffith's experiments demonstrated that a heat-killed pathogenic S strain transferred a "transforming principle" to a live nonpathogenic R strain, making it pathogenic. This was a key discovery, leading to the understanding that DNA is the material responsible for inheritance and transformation.

Explanation:

In Frederick Griffith's transformation experiments, something remarkable was observed. When Griffith injected a mouse with both the live nonpathogenic R strain and heat-killed pathogenic S strain of Streptococcus pneumoniae, the mouse died, and only the S strain was recovered.

This outcome was unexpected because separately, the live R strain did not kill the mice, and the heat-killed S strain could not cause illness either. Griffith's findings indicated that the nonpathogenic R strain had acquired the ability to form smooth colonies and become pathogenic from the heat-killed S strain.

Griffith concluded that the R strain must have taken up some transforming principle from the heat-killed S strain, which allowed it to become pathogenic. This transformative agent, initially hypothesized to be external DNA, was responsible for changing the morphology and physiology of the R strain, leading to the production of the protective polysaccharide capsule that is a characteristic of the pathogenic S strain. The capsule makes colonies appear smooth and enables the bacteria to evade the immune system, resulting in virulence.

These pivotal experiments played a crucial role in the discovery of DNA as the material of inheritance, paving the way for modern molecular genetics. The phenomenon observed by Griffith is now known as transformation, where genetic material from one cell can be taken up by another, incorporating new genetic information into its own genetic makeup.