Case Study Bacterial Transformation The Spanish flu outbreak which lasted from 1918 1919 was one of the most severe pandemics in recent history it is believed to have infected over 500 million and killed over 50 million people worldwide this is more than any other pandemic including COVID 19 This flu was caused by the HINI virus and was unusually deadly For the scientific community the outbreak of the Spanish Flu began a race to create a vaccine Vaccines prevent deadly and or dangerous diseases by working with the body s immune system to reduce the risk of infection and develop immunity against the disease two One of the leading causes of death for patients infected with the flu was a pneumonia infection in their lungs Due to this a British scientist named Frederick Griffith decided to focus his work on creating a vaccine to prevent pneumonia infections Pneumonia is caused by the bacterium Streptococcus pneumoniae Streptococcus pneumoniae forms the S strain and the R strain The S or smooth strain is covered with an outer coat known as a capsule and is highly virulent meaning it is able to cause the disease The R or rough strain has a rough appearance because it lacks a capsule and is therefore nonvirulent meaning it does not cause the disease Griffith was interested in researching ways to manipulate or change the S strain bacteria to alter its virulence Specifically he wanted to heat kill the cells to determine if that would reduce their virulence He planned to inject healthy mice with both the S and R strains 1 What is a possible hypothesis for Frederick Griffith s experiment Griffith Iypothesized that a chemical component from the vinulent S cells had somehow transformed the R cells into the more virulent S form To begin his experiments Griffith injected healthy mice with living S strain cells The mice contracted pneumonia and died Next Griffith injected healthy mice with living R strain cells The mice did not not contract pneumonia and they lived 2 Are these the results you would have expected given the information you know about the R and S strain bacterial cells Why or why not Yes because when harmless R bacteria were combined with harmless heat Killed S bacteria and inject into a mouse Not only did the mouse develop pneumonia and die R strain bacteria must have taken upd transforming princ From the heat Killed s bacteria which allowed them to transform Pito smooth coated bacteria and become 3 If both R and S cells are strains of Streptococcus pneumoniae why is it that the tradit Leaked the mice to develop pneumonia while the R strain did not This is because the DNA from the heat Killed SS 5 strain was able to be taken up by the R Strain This DNA gave the R strain its virulence and allowed it to infect the mouse cells and cause oneumonia and death Next Griffith took S strain cells and heated them The heating killed the cells He then took the heat killed S strain cells and injected them into a new set of healthy mice The mice did not contract pneumonia and they continued to live 4 Are these results what you would expect Why or why not Down With S Lastly Griffith took the heat killed S strain cells and mixed them with the living R cells He injected this mixture of cells into a new set of healthy mice The mice contracted pneumonia and died 5 Are these results what you would have expected Why or why not Griffith took samples from the mice that were injected with the mixture of heat killed S strain and living R strain cells To his surprise he found living cells with a capsule 6 If the S strain cells were heated and killed how was it possible for Griffith to find living cells with a capsule inside of the mice 7 Use the chart below to summarize Griffith s results Bacteria Result Living S cells Living R cells Heat killed S cells obuk Mixture heat killed S cells and living R cells ME After the surprising results of this experiment Griffith hypothesized that something in the heat killed S strain cells must have changed the R strain cells so that they were able to produce capsules and therefore become highly virulent Furthermore Griffith found that these living cells were able to reproduce and pass on their capsule and virulence to subsequent generations He now knew that whatever had changed these cells was heritable During this time very little was known about DNA so Griffith was never able to determine what caused the change in the bacteria but he termed this phenomenon transformation Griffith s surprise results did not lead to a vaccine but his work was not done in vain This famous experiment was a significant contribution to the scientific community because it helped spur other scientists to discover that DNA was the transforming principle We will come back to this important study later in the unit when we look at transformation more closely For now we will focus on learning more about DNA and the discoveries that this experiment led to 8 Review the experiment conducted by Griffith Identify the control group the experimental group and independent and dependent variables in Fords