Bacteria: Key Features and Structure

Bacteria: Key Features

• Bacteria are single-celled microorganisms.
• They are ancient life forms, sharing basic functions with other living cells.
• They lack chlorophyll, rely on external sources for energy.
• Bacteria have a single circular DNA chromosome located within their cytoplasm.
• They lack membrane-bound organelles, like mitochondria or a nucleus.

Bacterial Size & Shape

• Bacteria are measured in micrometers (µm).

Bacterial Arrangement

• Bacteria can exist as single cells or in groups, depending on the species.
• Arrangements include:
  • Cocci: Spherical or round bacteria.
  • Bacilli: Rod-shaped bacteria.
  • Spirilla: Spiral-shaped bacteria.

Bacterial Structure

• Flagellum: A whip-like tail that helps bacteria move.
• Ribosomes: Responsible for protein synthesis.
• Cytoplasm: The gel-like substance that fills the cell.
• Nucleoid: The region in the cytoplasm where the bacterial DNA is located.
• Plasma Membrane: A selectively permeable membrane that encloses the cell.
• Cell Wall: Provides structural support and protects the bacteria.
• Capsule: An outer layer that surrounds some bacteria, providing protection.
• Pilus: Hair-like structures that assist in attachment and the transfer of genetic material.

Gram Staining

• Differentiates bacteria based on their cell wall structure.
• Developed by Hans Christian Gram.
• Gram-positive bacteria: Have a thick peptidoglycan layer in their cell wall.
• Gram-negative bacteria: Have thin peptidoglycan layer but thick lipopolysaccharide layer.

Environmental Requirements

• Bacteria require specific conditions for growth and survival.
• Factors include:
  • Moisture: Essential to survive, some bacteria are adapted to arid environments.
  • Oxygen: Bacteria vary in their oxygen requirements.
  • Carbon: Essential for cell structure and function.
  • Dioxide: Necessary for cellular respiration.
  • Temperature: Tolerance varies depending on the bacteria.
  • pH: Specific hydrogen ion concentration optimal for growth.
  • Light: Some bacteria require light or are negatively impacted by it.
  • Osmotic effect: Resistance to changes in osmotic pressure.
  • Mechanical stress: Resiliency to physical stressors.

Naming Bacteria

• Taxonomy: The system used to classify organisms into groups, based on their characteristics.
• Kingdom: Procaryote, characterized by the absence of a distinct nucleus.
• Division: Firmicutes, bacteria with a low amount of DNA.
• Subdivision: Further classification based on properties.
• Family: Grouping of similar genera.
• Genus: A group of closely related species.
• Species: The basic unit of classification, containing individual organisms with similar characteristics.
• Naming example: Streptococcus mutans (S. mutans )

Dental Significance of Bacteria

• Some bacteria are associated with dental diseases, such as cavities (caries) and gum disease (periodontal disease).
• Streptococcus mutans is known for its role in tooth decay.