E. coli most likely becomes resistant to T4 phage through mutations in

A. the cell wall.

B. a restriction enzyme.

C. a modification enzyme.

D. the structure of pili.

E. the cytoplasmic membrane.


1. A researcher discovered a mutation in E. coli that prevented phage T4 but not lambda from lysing the cells. What would you surmise is the nature of this mutation?

2. A public health physician isolated large numbers of phage from rivers used as a source of drinking water in western Africa. The physician is very concerned about humans becoming ill from drinking this water although she knows that phages specifically attack bacteria. Why is she concerned?

Critical Thinking

1. Would transduction or conjugation be the most likely mechanism of gene transfer from a Gram-negative to a Grampositive organism? Explain the reason for your answer.

2. A filter capable of preventing passage of bacteria is placed at the bottom of a U tube to separate the two sides. Streptomycin-resistant cells of a bacterium are placed on one side of the filter and streptomycin-sensitive cells are placed on the other side. After incubation for 24 hours, the side of the tube that originally contained only streptomycin-sensitive cells now contains some streptomycin-resistant cells. Give three possible reasons for this observation. What further experiments would you do to determine the correct explanation?

3. A suspension of phage when added to a culture of bacteria lyses the cells. When a suspension of the same phage is added to bacteria that have been previously agitated in a blender, no lysis occurs. Explain.

4. Is it surprising that most phages are temperate and not virulent? Explain.

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