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Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 11 - The Prokaryotes: Domains Bacteria and ArchaeaProblem 3
Chapter 11, Problem 3

Draw a key to differentiate the following bacteria: cyanobacteria, Cytophaga, Desulfovibrio, Frankia, Hyphomicrobium, methanogens, myxobacteria, Nitrobacter, purple bacteria, Sphaerotilus, and Sulfolobus.

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Step 1: Begin by grouping the bacteria based on their major characteristics such as cell type (prokaryote or archaea), metabolism (photosynthetic, chemolithotrophic, heterotrophic), and morphology (shape, presence of special structures). For example, separate cyanobacteria and purple bacteria as photosynthetic groups, methanogens and Sulfolobus as archaea, and others as bacteria with distinct metabolic or structural traits.
Step 2: Identify key distinguishing features for each group. For instance, cyanobacteria are oxygenic photosynthetic bacteria with thylakoid membranes, while purple bacteria are anoxygenic photosynthetic bacteria using bacteriochlorophyll. Methanogens produce methane and belong to the Archaea domain, whereas Sulfolobus is a thermoacidophilic archaeon.
Step 3: Use morphological traits to differentiate genera such as Cytophaga (gliding motility, rod-shaped), Frankia (filamentous nitrogen-fixing bacteria), Hyphomicrobium (budding bacteria with prosthecae), and Sphaerotilus (sheath-forming bacteria).
Step 4: Incorporate metabolic or ecological roles to separate bacteria like Desulfovibrio (sulfate-reducing bacteria), Nitrobacter (nitrifying bacteria oxidizing nitrite to nitrate), and myxobacteria (social bacteria forming fruiting bodies).
Step 5: Organize these characteristics into a dichotomous key format, starting with broad distinctions (e.g., photosynthetic vs. non-photosynthetic, bacteria vs. archaea), then narrowing down by morphology and metabolism until each genus or group is uniquely identified.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bacterial Classification and Morphology

Understanding bacterial classification involves recognizing differences in cell shape, structure, and grouping. Morphological traits such as filamentous forms, cell size, and presence of specialized structures help differentiate bacteria like myxobacteria (social, gliding) and Sphaerotilus (sheath-forming). Morphology is a primary step in creating identification keys.
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Metabolic and Physiological Characteristics

Bacteria can be distinguished by their metabolic processes, such as photosynthesis in cyanobacteria and purple bacteria, sulfur reduction in Desulfovibrio, nitrogen fixation in Frankia, and methane production in methanogens. These physiological traits are critical for differentiating bacteria with similar morphology but distinct ecological roles.
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Phylogenetic and Environmental Adaptations

Phylogenetic relationships and environmental niches provide clues for differentiation. For example, Sulfolobus is an archaeon thriving in acidic hot springs, unlike typical bacteria. Recognizing such adaptations helps separate groups like archaea (Sulfolobus) from bacteria and understand their evolutionary context.
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Related Practice
Textbook Question

Compare and contrast each of the following:

a. Cyanobacteria and algae

b. Actinomycetes and fungi

c. Bacillus and Lactobacillus

d. Pseudomonas and Escherichia

e. Leptospira and Spirillum

f. Escherichia and Bacteroides

g. Rickettsia and Chlamydia

h. Mycobacterium and Mycoplasma

1346
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Textbook Question

Which of the following does not belong with the others?

a. Enterobacteriales

b. Lactobacillales

c. Legionellales

d. Pasteurellales

e. Vibrionales

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Textbook Question

Pathogenic bacteria can be

a. motile.

b. rods.

c. cocci.

d. anaerobic.

e. all of the above.

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Textbook Question

These organisms are important in sewage treatment and can produce a fuel used for home heating and for generating electricity.

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Textbook Question

If you Gram-stained the bacteria that live in the human intestine, you would expect to find mostly

a. gram-positive cocci.

b. gram-negative rods.

c. gram-positive, endospore-forming rods.

d. gram-negative, nitrogen-fixing bacteria.

e. all of the above.

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Textbook Question

Which of the following is an intracellular parasite?

a. Rickettsia

b. Mycobacterium

c. Bacillus

d. Staphylococcus

e. Streptococcus

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