Distinguish between Gram-positive and Gram-negative bacteria, and give an example of each.

Question

Summarize the evolutionary significance of cyanobacteria.
What are extremophiles? Name three types.
Describe two ways archaea are different from bacteria?
How can archaea reproduction be distinct from bacterial reproduction?
How do most archaea obtain energy?

Answer 1

Distinguishing Between Gram-positive and Gram-negative Bacteria

Gram-positive Bacteria:

• Cell Wall Structure: Have a thick peptidoglycan layer and no outer membrane. They retain the crystal violet stain used in the Gram staining process, appearing purple.
• Example: Staphylococcus aureus, often associated with skin infections.

Gram-negative Bacteria:

• Cell Wall Structure: Have a thinner peptidoglycan layer and are surrounded by an outer membrane, which contains lipopolysaccharides. They do not retain the crystal violet stain but take up the counterstain, appearing pink.
• Example: Escherichia coli, a common bacterium found in the intestines of humans and animals.

Evolutionary Significance of Cyanobacteria

Cyanobacteria are significant in evolutionary terms because they were among the first organisms to perform photosynthesis, generating oxygen as a byproduct. This process contributed to the Great Oxygenation Event, which dramatically changed Earth’s atmosphere and allowed aerobic life to flourish. Additionally, cyanobacteria played a crucial role in the development of chloroplasts through a process of endosymbiosis, leading to the evolution of plants.

Extremophiles

Extremophiles are organisms that thrive in extreme environmental conditions, such as high temperature, acidity, salinity, or pressure. They can be found in some of the most inhospitable environments on Earth.

Three Types of Extremophiles:

1. Thermophiles: Thrive at high temperatures (usually above 45°C). Example: Thermus aquaticus.
2. Halophiles: Prefer highly saline environments. Example: Halobacterium.
3. Acidophiles: Flourish in acidic conditions (pH lower than 3). Example: Ferroplasma.

Differences Between Archaea and Bacteria

1. Cell Membrane Composition:

   • Archaea have unique lipids in their cell membranes (ether linkages), while bacteria typically have ester-linked lipids. This difference affects the stability of their membranes under extreme conditions.

2. Genetic Machinery:

   • The machinery for protein synthesis, including ribosomal structure and the machinery for transcription and translation, is more similar to eukaryotes in archaea than in bacteria. The ribosomes of archaea resemble those of eukaryotes in size and function.

Distinct Reproduction of Archaea

Archaea can reproduce via a process called binary fission (similar to bacteria), but they can also reproduce through budding or fragmentation, which may lead to different cellular structures. Additionally, some archaea can engage in horizontal gene transfer, but the mechanisms and frequency may differ from those in bacteria since archaea may utilize unique plasmids or viruses for gene transfer.

Energy Acquisition in Archaea

Most archaea obtain energy in diverse ways, depending on their type:

• Chemolithoautotrophy: Many archaea derive energy by oxidizing inorganic substances (like hydrogen gas, sulfur, or ammonia), often in extreme environments like hydrothermal vents.
• Methanogenesis: A unique form of anaerobic respiration used by some archaea (methanogens) to produce methane from carbon dioxide and hydrogen, which is a significant part of the carbon cycle in anaerobic habitats.
• Phototrophy: Some archaea can also capture light energy through bacteriorhodopsin, although this is not as common as in cyanobacteria.

In summary, archaea exhibit unique metabolic and genetic characteristics that distinguish them from bacteria, while their versatility in energy acquisition allows them to thrive in various extreme environments.