Problem 2 - Brock Biology of Microorganisms

Question

Which phylum contains the bulk of known gram-negative bacteria? What subgroup of this phylum contains the bacterium Escherichia coli? Which contains Pseudomonas aeruginosa? (Sections 15.1-15.5)

Step-by-Step Solution

Answer

The phylum is Proteobacteria. Escherichia coli and Pseudomonas aeruginosa are in the Gammaproteobacteria subgroup.

Step 1 - Identify the Phylum

The first task is to determine which phylum contains the majority of known gram-negative bacteria. From sections 15.1 to 15.5, it is clear that the phylum Proteobacteria includes a wide range of gram-negative bacteria.

Step 2 - Determine the Subgroup for Escherichia coli

Escherichia coli, commonly associated with the human gut, falls under the subgroup known as Gammaproteobacteria within the phylum Proteobacteria.

Step 3 - Determine the Subgroup for Pseudomonas aeruginosa

Pseudomonas aeruginosa, a notable pathogen, is also part of the phylum Proteobacteria but belongs to the subgroup Gammaproteobacteria just like Escherichia coli.

Key Concepts

Gram-negative bacteria

Gram-negative bacteria are a diverse group of microorganisms with a distinctive cell wall structure. Their cell walls have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. This outer membrane makes them more resistant to certain antibiotics.
Gram-negative bacteria are characterized by:

• A unique cell wall structure
• Being more resistant to some antibiotics
• Including many significant human pathogens

They play critical roles in various environments, from human guts to soil ecosystems.

Gammaproteobacteria

Gammaproteobacteria is a large and diverse class within the phylum Proteobacteria. These bacteria are primarily gram-negative and include both free-living and pathogenic species. Some key points about Gammaproteobacteria include:

• Consisting mostly of gram-negative bacteria
• Having free-living and pathogenic species
• Playing essential roles in nitrogen fixation, sulfur reduction, and other important biochemical processes

Understanding this class helps in studying both environmental microbiology and pathology.

Escherichia coli

Escherichia coli, often referred to as E. coli, is a well-known bacterium that belongs to the Gammaproteobacteria class within the phylum Proteobacteria. E. coli is commonly found in the intestines of humans and other animals. Key characteristics of E. coli include:

• Residing mostly in the human gut
• Being essential for digestive health
• Having some strains that can cause foodborne illnesses

E. coli serves as a model organism in molecular biology and genetics due to its relatively simple genetics and ease of cultivation.

Pseudomonas aeruginosa

Pseudomonas aeruginosa is another gram-negative bacterium within the Gammaproteobacteria class of the Proteobacteria phylum. It is known for its versatility and ability to cause various infections, particularly in individuals with compromised immune systems. Key points about Pseudomonas aeruginosa include:

• Being an opportunistic pathogen
• Able to thrive in diverse environments
• Causing infections in respiratory systems, wounds, and burns

This bacterium is notable for its resistance to multiple antibiotics, making infections difficult to treat and necessitating advanced medical intervention.