Archaea identification — selecting a representative archaeal group Which microorganism group below is classified among the archaebacteria (Archaea)?

Introduction / Context:
Archaea constitute a distinct domain of life, often thriving in anaerobic or extreme environments. Familiarity with hallmark archaeal groups helps in environmental microbiology, biotechnology, and evolutionary studies.

Given Data / Assumptions:

• Archaea include methanogens, extreme halophiles, and thermoacidophiles.
• They possess ether-linked membrane lipids and unique rRNA signatures.
• We seek an example group commonly cited as archaeal.

Concept / Approach:
Methanobacteria (methanogens) generate methane from CO2 and H2 or acetate and are obligate anaerobes. They are archetypal Archaea. Cyanobacteria are oxygenic photosynthetic bacteria (Bacteria domain); Trichomonads are eukaryotic protists; Mycoplasma are bacterial; Spirochetes are Bacteria.

Step-by-Step Solution:
Identify archaeal hallmark metabolisms: methanogenesis is uniquely archaeal.Match “Methanobacteria” with methanogens.Exclude groups known to be Bacteria or Eukarya.

Verification / Alternative check:
Methanogens are routinely used as archaeal examples in textbooks and detected in anaerobic digesters and ruminant guts.

Why Other Options Are Wrong:

• A/D/E: These are Bacteria, not Archaea.
• C: Trichomonads are eukaryotic protists (no cell wall, have nuclei and flagella).

Common Pitfalls:
Assuming cyanobacteria are Archaea due to “ancient” reputation; they are Bacteria.

Final Answer:
Methanobacteria (methanogens)