Ch. 10 - Classification of Microorganisms

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 10 - Classification of Microorganisms

Problem 7

Chapter 10, Problem 7

The wall-less mycoplasmas are considered to be related to gram-positive bacteria. Which of the following would provide the most compelling evidence for this?
a. They share common rRNA sequences.
b. Some gram-positive bacteria and some mycoplasmas produce catalase.
c. Both groups are prokaryotic.
d. Some gram-positive bacteria and some mycoplasmas have coccus-shaped cells.
e. Both groups contain human pathogens.

Verified step by step guidance

Step 1: Understand the question is asking for the most compelling evidence that links wall-less mycoplasmas to gram-positive bacteria, focusing on evolutionary or genetic relationships rather than superficial traits.

Step 2: Evaluate each option by considering what type of evidence best indicates a close evolutionary relationship. For example, shared genetic sequences (like rRNA) are strong evidence of common ancestry.

Step 3: Recognize that options involving shared physical traits (such as cell shape or enzyme production) or general characteristics (being prokaryotic or pathogenic) are less definitive because these traits can be found in many unrelated groups due to convergent evolution or common functions.

Step 4: Identify that shared rRNA sequences (option a) provide molecular evidence, which is widely accepted in microbiology as a reliable method to determine phylogenetic relationships among bacteria.

Step 5: Conclude that the most compelling evidence would be molecular data showing similarity in rRNA sequences, as this reflects evolutionary lineage more accurately than phenotypic traits.

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Key Concepts

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

Phylogenetic Relationship and rRNA Sequencing

rRNA sequencing is a molecular tool used to determine evolutionary relationships among organisms. Similarities in rRNA sequences indicate a close genetic relationship, making it a strong method to link mycoplasmas to gram-positive bacteria despite differences in cell structure.

Cell Structure and Gram Staining

Gram-positive bacteria have thick peptidoglycan cell walls, while mycoplasmas lack cell walls entirely. This structural difference affects staining and morphology, so shared physical traits like shape or enzyme production are less reliable for determining relatedness.

Phenotypic Traits vs. Genetic Evidence

Phenotypic traits such as catalase production, cell shape, or pathogenicity can be found across diverse bacteria and do not necessarily indicate close evolutionary relationships. Genetic evidence, like rRNA sequence similarity, provides more compelling proof of relatedness.

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Related Practice

Textbook Question

Use the following choices to answer questions 7 and 8.

a. Animalia

b. Fungi

c. Plantae

d. Bacillota (gram-positive bacteria)

e. Pseudomonadota (gram-negative bacteria)

Into which group would you place a multicellular organism that has a mouth and lives inside the human liver?

Textbook Question

Use the following choices to answer questions 7 and 8.

a. Animalia

b. Fungi

c. Plantae

d. Bacillota (gram-positive bacteria)

e. Pseudomonadota (gram-negative bacteria)

Into which group would you place a photosynthetic organism that lacks a nucleus and has a thin peptidoglycan wall surrounded by an outer membrane?

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Textbook Question

Use the key in the Clinical Focus box to identify the gram-negative, oxidase-positive rod causing pneumonia in a sea otter. It is H₂S-positive, indole-negative, and urease-positive.

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Textbook Question

Use the following choices to answer questions 9 and 10.

1. 9 + 2 flagella

2. 70s ribosome

3. fimbria

4. nucleus

5. peptidoglycan

6. plasma membrane

Which is (are) found only in prokaryotes?

a. 1,4,6

b. 3,5