5. Genetics of Bacteria and Viruses

What is a plasmid?

True or False:All bacterial cells within a bacteria colony grown on a plate in a laboratory are genetically identical.

Which of the following is NOT a way scientists can phenotypically identify a bacterial mutation?

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

The serine biosynthetic pathway is a three-step pathway in which each step is catalyzed by the enzyme product of a different gene, identified as enzymes A, B, and C in the diagram below.

Mutant 1 grows only on  In addition to growth on , mutant 2 also grows on  and . Mutant 3 grows on  and . Identify the step of the serine biosynthesis pathway at which each mutant is defective.

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

The three colonies that do not grow on minimal medium are transferred to minimal medium supplemented with the amino acid serine  and all three colonies grow. Characterize these three colonies.

Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

Using terminology from the chapter, characterize the 12 colonies that grow on minimal medium and the 3 colonies that do not.

What is lateral gene transfer? How might it take place between two bacterial cells?

Lateral gene transfer is thought to have played a major role in the evolution of bacterial genomes. Describe the impact of LGT on bacterial genome evolution.

A 2013 CDC report identified the practice of routinely adding antibiotic compounds to animal feed as a major culprit in the rapid increase in the number of antibiotic-resistant strains. Agricultural practice in recent decades has encouraged the addition of antibiotics to animal feed to promote growth rather than to treat disease.

How might the increase in antibiotic-resistant strains of bacteria in cattle be a threat to human health?

A 2013 CDC report identified the practice of routinely adding antibiotic compounds to animal feed as a major culprit in the rapid increase in the number of antibiotic-resistant strains. Agricultural practice in recent decades has encouraged the addition of antibiotics to animal feed to promote growth rather than to treat disease.

Speculate about the process by which feeding antibiotics to animals such as cattle might lead to an increase in the number of antibiotic-resistant strains of bacteria.

Devise an experiment to identify bacteria that are auxotrophic and unable to produce two amino acids, lysine (lys) and valine (val). The auxotrophic bacteria are in a pool of bacteria in which all the other bacteria are prototrophic. The genotype of the auxotrophs is lys⁻ val⁻. Describe each step in the experiment, identify the constituents in any growth medium or growth plates you propose, and identify the results that will conclusively identify bacteria that are lys⁻ val⁻.

Fifty bacterial colonies are on a complete-medium growth plate. The colonies are replica plated to a minimal-medium plate, and 46 colonies grow. What can you say about the bacteria from the four colonies that do not grow? Design an experiment and describe the methods you would use to determine if any of these four colonies are leu⁻, arg⁻, or val⁻.