Final answer:
In Griffith's experiments, the nonlethal R-strain bacteria were transformed into lethal S-strain bacteria through the process of transformation, involving the uptake of DNA from heat-killed S-strain bacteria.
Step-by-step explanation:
In the groundbreaking experiments of Griffith, the conversion of nonlethal R-strain bacteria to lethal S-strain bacteria was due to the process known as transformation. This transformation occurred when the R-strain bacteria took up the DNA from the heat-killed S-strain bacteria, which contained the genetic information for pathogenicity, including the production of a protective capsule.
Griffith's finding was significant because it demonstrated that a substance from a dead bacteria could genetically transform living bacteria. While Griffith himself did not identify the substance as DNA, later experiments by Avery, MacLeod, and McCarty confirmed DNA as the transforming principle that carried genetic information and could transform the characteristics of an organism.