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Chapter 8: Problem 14

A plaque assay is performed beginning with \(1.0 \mathrm{mL}\) of a solution containing bacteriophages. This solution is serially diluted three times by taking \(0.1 \mathrm{mL}\) and adding it to \(9.9 \mathrm{mL}\) of liquid medium. \(0.1 \mathrm{mL}\) of the final dilution is plated and yields 17 plaques. What is the initial density of bacteriophages in the original \(1.0 \mathrm{mL} ?\)

Short Answer

Expert verified
Answer: The initial density of bacteriophages in the original 1.0 mL solution is 170,000 plaques/mL.

Step by step solution

01

Find the dilution factor for each step

At each serial dilution, 0.1 mL is taken from the solution and added to 9.9 mL of liquid medium. The dilution factor is calculated as the total volume divided by the sample volume. In this case, the dilution factor for each step is \(\frac{9.9 + 0.1}{0.1} = 10\)
02

Calculate the total dilution factor

Since there are three serial dilutions, we need to multiply the dilution factor for each step together to find the total dilution factor: \(10 \times 10 \times 10 = 1000\)
03

Calculate the density of bacteriophages in the last dilution

We know that 0.1 mL of the last dilution yielded 17 plaques. To find the density of bacteriophages in the last dilution, we need to divide the number of plaques by the volume plated: \(\frac{17 \text{ plaques}}{0.1 \text{ mL}} = 170 \text{ plaques/mL}\)
04

Calculate the initial density of bacteriophages

To find the initial density of bacteriophages in the original 1.0 mL solution, we need to multiply the density of the last dilution by the total dilution factor: \(170 \text{ plaques/mL} \times 1000 = 170000 \text{ plaques/mL}\) So, the initial density of bacteriophages in the original \(1.0 \mathrm{mL}\) solution is \(170,000\) plaques/mL.

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Most popular questions from this chapter

With respect to \(\mathrm{F}^{+}\) and \(\mathrm{F}^{-}\) bacterial matings, (a) How was it established that physical contact was necessary? (b) How was it established that chromosome transfer was unidirectional? (c) What is the genetic basis of a bacterium being \(\mathrm{F}^{+}\) ?

Describe the temporal sequence of the bacteriophage life cycle.

In this chapter, we have focused on genetic systems present in bacteria and the viruses that use bacteria as hosts (bacteriophages). In particular, we discussed mechanisms by which bacteria and their phages undergo genetic recombination, the basis of chromosome mapping. Based on your knowl- edge of these topics, answer several fundamental questions: (a) How do we know that bacteria undergo genetic recombination, allowing the transfer of genes from one organism to another? (b) How do we know that conjugation leading to genetic recombination between bacteria involves cell contact, which precedes the transfer of genes from one bacterium to another? (c) How do we know that during transduction bacterial cell-tocell contact is not essential?

Describe the difference between the lytic cycle and lysogeny when bacteriophage infection occurs.

In the plaque assay, exactly what makes up a single plaque?
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