Bacteria are single-celled, prokaryotic microorganisms that are found in virtually every environment on Earth.
They belong to the domain Bacteria, one of the two domains of prokaryotes, the other being Archaea.
Bacteria are among the earliest forms of life, appearing about 3.5 billion years ago.
The ultra-structure of bacteria refers to the detailed structure of bacterial cells as observed under an electron microscope.
This allows for the visualization of cellular components that are not visible with a light microscope.
Importance of Bacteria
1. Ecological Role:
Bacteria play crucial roles in nutrient cycling, such as nitrogen fixation, decomposition, and bioremediation.
2. Human Health:
While some bacteria cause diseases, many are beneficial for human health, aiding in digestion and synthesizing essential vitamins.
3. Industrial Applications:
Bacteria are used in the production of antibiotics, fermentation processes (like yogurt and cheese making), and biotechnology (such as genetic engineering).
Key Components of Bacterial Ultra-structure:
1. Cell Envelope:
A. Cell Wall: Provides shape and protection. Made of peptidoglycan in most bacteria.
i. Gram-positive bacteria: Thick peptidoglycan layer with teichoic acids.
ii. Gram-negative bacteria: Thin peptidoglycan layer, outer membrane with lipopolysaccharides (LPS).
B. Cell Membrane (Plasma Membrane): Phospholipid bilayer that controls the passage of substances in and out of the cell.
2. Cytoplasm:
A. Nucleoid: Region where the bacterial chromosome (circular DNA) is located.
B. Ribosomes: Sites of protein synthesis, smaller than eukaryotic ribosomes (70S).
C. Plasmids: Small, circular DNA molecules that replicate independently of the chromosome and can carry genes for antibiotic resistance, virulence factors, etc.
D. Inclusion Bodies: Storage granules for nutrients, waste products, or other substances.
3. Surface Structures:
A. Capsule: Gelatinous layer outside the cell wall, protects against phagocytosis and desiccation.
B. Flagella: Long, whip-like structures used for locomotion.
C. Pili (Fimbriae): Hair-like projections used for attachment to surfaces or other cells and in some cases for conjugation (transfer of genetic material between bacteria).
4. Endospores:
Highly resistant structures formed by some Gram-positive bacteria (e.g., Bacillus, Clostridium) under adverse conditions to ensure survival.