KINGDOM MONERA

 

Kingdom Monera: 

1. Characteristics of Kingdom Monera

1.1 General Features:

• Cell Type: Prokaryotic, meaning cells lack a true nucleus and membrane-bound organelles.
• Cellularity: Unicellular.
• Size: Typically between 0.1 µm and 15 µm in diameter.
• Shape: Common shapes include:
  • Cocci: Spherical (e.g., Streptococcus).
  • Bacilli: Rod-shaped (e.g., Escherichia coli).
  • Spirilla: Spiral-shaped (e.g., Helicobacter pylori).
  • Vibrios: Comma-shaped (e.g., Vibrio cholerae).

1.2 Cell Structure:

• Cell Wall:

  • Bacteria: Composed mainly of peptidoglycan (also known as murein).
    • Gram-Positive Bacteria: Thick peptidoglycan layer which retains crystal violet stain, appearing purple.
    • Gram-Negative Bacteria: Thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides. They do not retain crystal violet and appear pink after staining with safranin.
  • Archaea: Cell walls lack peptidoglycan; instead, they may have pseudopeptidoglycan or other polysaccharides.

• Plasma Membrane:

  • Phospholipid bilayer with proteins, similar to eukaryotic membranes, but lacks sterols.

• Genetic Material:

  • Nucleoid: Region within the cell containing the circular DNA molecule, not membrane-bound.
  • Plasmids: Small, circular DNA fragments that can replicate independently and often carry genes beneficial for survival (e.g., antibiotic resistance).

• Ribosomes:

  • Smaller 70S ribosomes (compared to 80S ribosomes in eukaryotes), responsible for protein synthesis.

• Other Structures:

  • Capsules: Some bacteria have an outer capsule that provides protection and helps in adherence to surfaces.
  • Pili/Fimbriae: Hair-like structures used for attachment to surfaces and in conjugation.
  • Flagella: Long, whip-like structures used for movement; may be single or multiple, and can be located at different positions on the cell.

2. Nutrition and Metabolism

2.1 Nutrition Types:

• Autotrophic:

  • Photoautotrophs: Use light energy to synthesize organic compounds from carbon dioxide (e.g., cyanobacteria).
  • Chemoautotrophs: Obtain energy from the oxidation of inorganic compounds (e.g., nitrifying bacteria).

• Heterotrophic:

  • Saprotrophic: Decompose dead organic matter (e.g., Bacillus subtilis).
  • Parasitic: Live on or within a host, often causing disease (e.g., Mycobacterium tuberculosis).
  • Symbiotic: Form mutualistic relationships with other organisms (e.g., Rhizobium in legume root nodules).

2.2 Respiration Types:

• Aerobic Respiration: Requires oxygen (e.g., Mycobacterium).
• Anaerobic Respiration: Does not require oxygen; can be obligate or facultative. Some anaerobes are harmed by oxygen (e.g., Clostridium botulinum), while others can grow in the presence or absence of oxygen (e.g., Escherichia coli).

3. Reproduction and Genetic Variation

3.1 Reproduction:

• Binary Fission: Asexual reproduction where a single cell divides into two identical daughter cells. It is a rapid process and can occur every 20 minutes under optimal conditions.

3.2 Genetic Variation:

• Mutation: Spontaneous changes in DNA sequences, which can lead to new traits.
• Horizontal Gene Transfer:
  • Conjugation: Direct transfer of DNA between two bacterial cells through a pilus.
  • Transformation: Uptake of free DNA from the environment by a bacterial cell.
  • Transduction: Transfer of DNA from one bacterium to another by a bacteriophage (virus).

4. Classification

4.1 Bacteria:

• Gracilicutes: Gram-negative bacteria (e.g., Escherichia coli).
• Firmicutes: Gram-positive bacteria (e.g., Bacillus anthracis).
• Actinobacteria: High-GC Gram-positive bacteria (e.g., Mycobacterium tuberculosis).
• Cyanobacteria: Photosynthetic bacteria formerly known as blue-green algae (e.g., Anabaena).

4.2 Archaea:

• Methanogens: Produce methane as a metabolic byproduct (e.g., Methanobacterium).
• Halophiles: Thrive in extremely saline environments (e.g., Halobacterium).
• Thermophiles: Live in extremely high temperatures (e.g., Thermococcus).

5. Ecological and Economic Importance

5.1 Ecological Roles:

• Decomposers: Breakdown of organic matter, recycling nutrients back into the ecosystem.
• Nitrogen Fixation: Conversion of atmospheric nitrogen into a form usable by plants (e.g., Rhizobium in legume root nodules).

5.2 Human Health:

• Beneficial Bacteria: Probiotics aid in digestion and immune function.
• Pathogens: Cause diseases such as tuberculosis (Mycobacterium tuberculosis), cholera (Vibrio cholerae), and various other infections.

5.3 Biotechnology:

• Genetic Engineering: Use of bacterial plasmids for cloning and gene manipulation.
• Industrial Applications: Production of antibiotics, enzymes, and other biochemicals (e.g., insulin production using genetically modified bacteria).

6. Key Terms:

• Peptidoglycan: Polymer of sugars and amino acids forming the cell wall in bacteria.
• Plasmid: Small, circular DNA molecule within bacteria.
• Binary Fission: Process of asexual reproduction in bacteria.
• Conjugation: Transfer of genetic material between bacterial cells.

7. Examples:

• Bacteria:
  • Escherichia coli (common gut bacterium).
  • Streptococcus pneumoniae (causes pneumonia).
  • Clostridium tetani (causes tetanus).
• Archaea:
  • Methanobacterium (methane-producing archaea).
  • Halobacterium (salt-loving archaea).
  • Thermococcus.