Prescott’s Microbiology, 9 th
Edition
Chapter 22 –The Proteobacteria
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
Figure 22.4 What would Rhodospirillum rubrum use for carbon and energy sources if grown (a) anaerobically in the dark in the presence of malate, (b) anaerobically in the light without organic carbon, and (c) aerobically in the light in the presence of malate?
(a) Using the flowchart, anaerobic dark metabolism is chemoorganotrophy, fermenting malate.
(b) Anaerobic metabolism in the light without organic carbon is photoautotrophy, requiring hydrogen gas or hydrogen sulfide as electron donors.
(c) Aerobic metabolism, regardless of light availability, is chemoorganotrophic respiration, in this case, using malate as the carbon and energy source.
Figure 22.5 What is the purpose of the annular stop in a phase-contrast microscope? Is it found in any other kinds of light microscopes?
Using an annular stop and an objective phase plate, the microscope can be aligned to superimpose illuminating light rays passed through the annulus onto the objective phase ring to achieve phase-contrast illumination. Dark field microscopy uses a dark field stop similar to the annular ring to produce a hollow cone of light and differential interference contrast microscopy uses prisms to generate the two beams of light.
Figure 22.9 If Caulobacter were grown in a phosphate-limited broth, what would happen to the length of the stalks?
The stalks grow longer in nutrient deprived media, presumably to increase surface area and nutrient uptake.
Figure 22.14 What steps are also found in the TCA cycle? What is the structural difference between serine and glycine?
The oxaloacetate to malate step is in the TCA cycle in the reverse direction. The side chain for serine is CH
2
OH while the side chain for glycine is H.
Figure 22.15 Why do nitrifying microbes possess intracellular membranes?
Nitrifying microbes possess intracellular membranes to increase the surface area available for electron transport.
Figure 22.17 Why does N.europaea
have PTS transport systems for the sugars fructose and mannose if it is autotrophic?
Students should note that autotrophs should obtain carbon from inorganic sources. The bacteria does use the Calvin cycle to fix CO
2
. Presence of the PTS systems could mean several things, which students should propose. It could be other uses for the sugars, such as incorporating mannose or fructose into glycoproteins and glycolipids. Or it might suggest that the organism could also use these as carbon sources. A number of bacteria can be placed into more than one metabolic category.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.

Prescott’s Microbiology, 9 th
Edition
Figure 22.18 Identify the reactions that contribute to substrate level phosphorylation and those that might contribute to ATP synthesis by a membrane-bound ATP synthase.
ATP sulfurylase and APS:APAT then catalyze the exchange of the sulfate on APS with PPi to generate
ATP via substrate-level phosphorylation. Electrons from sulfite can be donated to an electron transport chain via sulfite dehydrogenase within the membrane.
Figure 22.24 Given that bacteria must depend on membrane transport and intracellular diffusion of nutrients, why is it important that a microbe the size of T. namibiensis contain a central vacuole rather than cytoplasm?
The hollow shape promotes transport and diffusion, while a solid cell has a much lower cell volume to surface area ratio.
Figure 22.27 How does the ribulose monophosphate pathway compare to the serine pathway
(figure 22.14) in terms of energy and reducing power used? What might be the ecological consequence of this difference?
The ribulose monophosphate pathway consumes one ATP to generate the 3C molecule G3P.
The serine pathway consumes two ATP and oxidizes two NADH to generate the 2C molecule acetyl-CoA. Therefore, the serine pathway uses up reducing power while the ribulose does not.
Figure 22.28 Do you think a Gram-positive microbe could use an insoluble metal as an terminal electron acceptor in the same way Shewanella does in (a)?
Gram negative bacteria such as Shewanella localize cytochromes in the outer membrane (instead of the plasma membrane) and this enables the direct transfer of electrons from the cytochromes to the extracellular metal. Gram positive bacteria have a thick peptidoglycan layer exterior to their plasma membrane so this mechanism would not be possible.
Figure 22.30 Why do you think the FDH-O and FDH-N are on the periplasmic face of the plasma membrane while FDH-H is on the cytoplasmic face?
FDH-O and FDH-N need electron acceptors (oxygen and nitrate respectively), which are present in higher concentrations in the periplasm. FDH-H is active during fermentation, in which the organic electron acceptor is generated inside the bacteria.
Figure 22.31 What would be the identity of a motile microbe that synthesizes the enzyme betagalactosidase, assimilates citrate, produces DNase, and liquefies gelatin?
The genus Serratia fits those results.
Figure 22.36 How could the analysis of motility mutants be used to determine if the adhesion complexes are used in both S and A motility?
If adhesion complexes are involved in both types of motility, then mutants that lack the adhesion complexes would lose both S and A motility, while mutants lacking pili would only lose S motility and mutants lacking the cytoskeletal fiber would only lose A motility. On the other hand, if adhesion complexes are not involved, then their deletion would not affect motility.
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© 2014 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.