What happens when heat-killed S-strain pneumococcus were injected into a mouse along with live R-strain pneumococcus?

Answer 1

A very important characteristic about bacteria actually created live S-strain to exist in the dead injected mouse. Bacteria is competent, in biological terms, meaning that cells can take up "naked" DNA from it's environment.

Knowing that fact, when the heat-killed S-strain pneumoccus mixed with the live R-strain, the R-strain took in the DNA, therefore inheriting the deadly coating of the S-strain. So the R became S, and killed the mouse.

Answer 2

The mouse would not develop pneumonia as the heat-killed S-strain cannot cause infection. However, the R-strain pneumococcus would be able to cause infection in the mouse. This experiment by Griffith in 1928 demonstrated that genetic material from the heat-killed S-strain could transform the live R-strain into a virulent form.