Thermophiles taxonomy check: Thermus (commonly Thermus thermophilus) is best classified as which of the following?

Introduction / Context:
Thermophilic bacteria such as Thermus thrive at high temperatures and are important in biotechnology (e.g., thermostable enzymes). Accurate classification influences expectations about cell envelope structure and staining behavior.

Given Data / Assumptions:

• Genus: Thermus (e.g., Thermus thermophilus).
• We must determine Gram reaction and domain-level placement.
• Archaea differ from Bacteria in lipid chemistry and cell wall polymers.

Concept / Approach:

Thermus belongs to the phylum Deinococcus–Thermus within the domain Bacteria (eubacteria). Members generally stain Gram-negative due to a thin peptidoglycan layer and a characteristic envelope, though some may show variable staining. They are not archaea; archaea thermophiles include genera like Sulfolobus and Thermoplasma, which have distinct membrane lipids and pseudopeptidoglycan or S-layer walls.

Step-by-Step Solution:

Verification / Alternative check:

Genomic analyses and cell envelope studies place Thermus within Bacteria. Staining profiles and outer membrane components are consistent with Gram-negative-like traits, even in thermophilic adaptations.

Why Other Options Are Wrong:

• Gram-positive eubacteria: does not fit envelope structure for Thermus.
• Archaebacteria options: incorrect domain; Thermus is not archaeal.

Common Pitfalls:

• Equating “thermophile” with Archaea; many thermophiles are bacteria.
• Confusing Deinococcus (often Gram-positive stain) with Thermus; they share a phylum but differ in staining traits.

Final Answer:

Gram-negative eubacteria