Download Prescott`s Microbiology, 9th Edition Chapter 19 –Microbial

Prescott’s Microbiology, 9th Edition
Chapter 19 –Microbial Taxonomy and the Evolution of Diversity
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
Figure 19.2 Would this curve be shifted to the left or the right for a microbe with an
exceptionally low G + C composition? Explain your answer.
Unsure student understand that melting means the hydrogen bonds and hydrophobic base
stacking interactions between strands are disrupted. The covalent bonds connecting nucleotides
within each strand are not affected, thus melting is reversible. GC rich DNA is more stable than
AT rich, thus as the GC content decreases, the Tm decreases, so the curve shifts to the left.
Figure 19.4 Why does isolate #2 yield only one DNA fragment (band)?
The two fragments generated by the BamHI restriction digestion are both 6 kb in size, and
therefore run in the gel at the same location, and give only one band.
Figure 19.11 On what evidence is this hypothesis based?
Mitochondria and chloroplasts have double membranes, contain their own DNA as a single,
circular chromosome, divide by binary fission, and have 70S instead of 80S ribosomes.
Figure 19.12 Construct a scenario in which each of the following factors lead to the establishment
of two ecotypes from a single common ancestor, as shown in (b): the availability of carbon and
nitrogen sources; terminal electron acceptor; and mean local temperature.
There would be genetic variation in the original population followed by selective pressure and
the emergence of two ecotypes. Students can devise a variety of scenarios, such as a declining
carbon source on an agar media plate, or lowering mean temperate in a pond as the winter
approaches.
Figure 19.13 Which do you think would have a pan-genome more closely related to its core
genome: a microbial species whose strains are obligate intracellular symbionts, or a species
whose strains constitute the normal flora of the mammalian gut? Explain your answer.
Symbionts are in niche environments, often alone, and thus experience less HGT. Their core and
pan genomes mostly overlap. However, microbes in biomes that are highly competitive and
have numerous species, such as the gut, have high levels of HGT, and thus an expanded pan
genome.
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