MB 409 - Microbial Diversity - Midterm Exam #2


1. What are the three main evolutionary groups (Domains) of living things? (5 points)

Bacteria, Archaea, and Eucarya



2. Indicate the predominantly thermophilic evolutionary groups and their thermophilic ancestry by filling in the branches on the bacterial tree below. (10 points)

3. Deinococcus radiodurans is known for its extreme resistance to gamma and X radiation. What is the basis for this resistance, and why is it important for the organism? (5 points)

Extremely efficient DNA repair systems, important because D. radiodurans lives in cloud droplets where they are exposed to very high levels of DNA-damaging radiation.


4. Describe how the use of DNA polymerase from Thermus aquaticus improved polymerase chain reaction (PCR) technology. (5 points)

Since the enzyme is thermostable, it is not destroyed in the heat-denaturation step of PCR and so doesn't have to be replenished each cycle. Because of this, the cycling process is easily automated.


5. How do the stalks of alpha-purple Bacteria (e.g. Caulobacter crescentus) differ from those of the Planctomycetes (e.g. Planctomyces bekefii)? (5 points)

The stalks of the alpha-purple (prosthecate) bacteria are cytoplasmic extensions of the cell, wheras those of the Planctomycetes are fibrous structures than are external to the cell.


6. Describe the three methods used by Bacteria for motility. (5 points each)

Flagella
ATP-driven helical propellers

Gliding
Pores secrete polysaccharide - hydration expansion provides force like a rocket engine

Spirochaetes
Flagella in periplasmic space rather than external, forming axial fiber
Rotation of the flagella somehow turns the cell & drives it forward


7. How does Mycoplasma genitalium survive, given that it doesn't have any of the genes for the enzymes of TCA/Krebs cycle or amino acid biosynthetic pathways? (5 points)

The Mycoplasma are obligate intracellular parasites - they get all of the amino acids and metabolic compounds they need directly from their host.


8. How do the spores produced by the "low G+C" and "high G+C" subdivisions of the Gram-positive Bacteria differ? (10 points)

The low G+C Gram-positive bacteria produce endospores that are not reproductive (only one is formed) but is extremely resistant to environmental conditions, whereas the hifg G+C species produce reproductive spores that are not particularly resistant but are readily dispersed in the air.


9. Describe any bacterial developmental or life cycle.(10 points)

Some possible examples that could be described:

10. Compare the conjugative transfer of F plasmid with the spread of M13 infection. (10 points)

11. Give a description of any bacterial species or group that you find interesting. (5 points)

e.g. for Thermotoga:
All are thermophilic (65-90C), anaerobic fermentative rods (protons or sulfur used as e- acceptor to make H2 or H2S). Cells enclosed in a loose sheath, or 'toga' - this is the outer membrane of a Gram-negative-type envelope. Isolated from geothermally-heated soils (solfataras) & marine sediments


12. On the diagram of anoxygenic photosynthesis below, show how an organism would make the NADPH needed for CO2 fixation using H2S as the electron donor. (10 points)