Which of the following best explains why there are no gram-positive archaea species, but there are gram-positive bacteria species?

• A. Archaea are unable to grow in laboratory conditions required for Gram staining.
• B. Archaea have a thicker peptidoglycan layer than bacteria, making them always gram-negative.
• C. Archaea lack peptidoglycan in their cell walls, so they do not retain the crystal violet stain used in Gram staining.
• D. Gram-positive staining is only possible in organisms with an outer membrane, which archaea possess.

Answer: (C)

Verified step by step guidance

1. Understand the principle behind Gram staining: Gram staining differentiates bacteria based on the structure of their cell walls, specifically the presence and thickness of peptidoglycan layers.
2. Recall that Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which retains the crystal violet stain, appearing purple under a microscope.
3. Recognize that archaea have cell walls, but these walls do not contain peptidoglycan; instead, they have other polymers such as pseudopeptidoglycan or different proteins and polysaccharides.
4. Since Gram staining relies on peptidoglycan to retain the crystal violet stain, archaea do not retain this stain and therefore do not appear Gram-positive or Gram-negative in the traditional bacterial sense.
5. Conclude that the absence of peptidoglycan in archaeal cell walls explains why there are no Gram-positive archaea species, unlike bacteria which can be Gram-positive due to their thick peptidoglycan layers.