Student ID Date Section A: Genetics A broth culture of his Salmonella typhimuriu
ID: 202809 • Letter: S
Question
Student ID Date Section A: Genetics A broth culture of his Salmonella typhimurium is inoculated onto an agar plate that does not contain histidine. No other chemicals (possible mutagens) have been added. After incubation, several colonies are observed. Explain 1. 2. A broth culture of his S. typhimurium is inoculated onto an agar plate that does not contain histidine. A strongly mutagenic chemical is added, but no evidence of mutations shows up after incubation. Why? Hint: Review Step 1 of the Ames test procedure and consider at which stage during the life cycle of a microbe a mutation would take place. 3. The strain of his S. yphimurium is unable to make anyone ill, for it requires a histidine-rich environment for growth. Yet, extreme care should be taken to prevent contamination and potential infection when performing this test. Why? 84Explanation / Answer
1. A broth culture of histidine negative Salmonella typhimurium was plated onto an agar plate without histidine and mutagenic agents, still few colonies were observed on the agar plate because few of them revert back their ability to synthesize histidine by natural back mutation.
2. No evidence of mutation was found even after incubating with a strong mutagenic compound because the effect of mutagenic compounds can only be profound when the bacteria is actively replicating its DNA in the logarithmic phase, then the effect of the mutation will be seen.
3. Extreme care must be taken while experimenting with histidine negative Salmonella typhimurium because once the bacteria come in contact with the inner lumen of the body it will be able to retrieve histidine from the surrounding and start replicating and produce infection.