Diversity of Life: Bacteria (NSC262S)

Bacteria

  • Definition: Prokaryotic cells lacking a nucleus.
  • Prevalence: Found nearly everywhere on Earth.
  • Abundance: Grow in vast numbers, sometimes visible without aid.
  • Classification:
    • Eubacteria
    • Archaebacteria
  • Size: Smaller of the two kingdoms (Eubacteria and Archaebacteria).

Cell Structure

  • Basic Components:
    • Chromosome (DNA)
    • Plasma membrane
    • Cytoplasm
    • Plasmids (DNA)
    • Cell wall
  • Additional Structures:
    • Granule
    • Capsule (slime layer)
    • DNA in Nucleoid
    • Ribosome
    • Flagellum

Eubacteria

  • Classification: Larger of the two prokaryote kingdoms.
  • Cell Wall: Generally surrounded by a cell wall made of complex carbohydrates.

Cyanobacteria

  • Type: Photosynthetic bacterium.
  • Color: Bluish-greenish.
  • Photosynthesis: Possess membranes for photosynthesis.
  • Chloroplasts: Lack the same type of chloroplasts as plants.
  • Habitat: Found nearly everywhere on Earth.
  • Survival: Can survive in extremely hot and cold environments.

Archaea Bacteria

  • Cell Walls: Lack key carbohydrates found in eubacterial cell walls.
  • Cell Membrane: Contain different lipids in their cell membrane.
  • Ribosomes: Different types of ribosomes compared to eubacteria.
  • Gene Sequences: Possess very different gene sequences.
  • Habitats: Live in extremely harsh environments.
  • Oxygen Requirements: Do not require oxygen.
  • Extreme Conditions: Can thrive in extremely salty and hot environments.

Identifying Prokaryotes

  • Cell Shape: Cocci (sphere-shaped), Bacillus (rod-shaped), Spirillum (spiral-shaped).
  • Cell Wall Composition: Gram + and Gram - types indicate different chemical natures.
  • Movement: Flagella (leg-like structures for propulsion).

Bacterial Shapes

  • Cocci: Sphere-shaped bacteria.
  • Bacillus: Rod-shaped bacteria.
  • Spirillum: Spiral-shaped bacteria.
  • Flagella: Leg-like structures that propel the bacterium.

Gram Staining

  • Purpose: Determines the chemical nature of a cell wall.
  • Process: Gram staining reveals the color of the cell.
  • Result: Color indicates the type of carbohydrates in the cell wall.

Cell Walls

  • Gram-positive:
    • Capsule
    • Peptidoglycan
    • Plasma membrane
  • Gram-negative:
    • Outer membrane
    • Peptidoglycan
    • Periplasmic space
    • Plasma membrane

Movement

  • Flagella: Tail-like structure that whips around to propel the bacterium.
  • Cilia: Short hair-like structures moving in a beating motion to help the cell "swim".
  • Non-motile: Sticky cilia-like structures preventing movement.

Flagella Types

  • Peritrichous flagella
  • Polar flagella

Energy Acquisition

  • Autotrophs: Make their own energy.
    • Using solar energy (e.g., cyanobacteria).
    • Using chemical energy (chemotrophs, e.g., Archaea bacteria).
      • Examples:
        • Pyrococcus sp. (sulfur-dependent archaebacterium)
        • Halococcus sp.
        • Methanogen (stomach of ruminant)
  • Heterotrophs: Obtain food by eating (e.g., E. coli).

Autotrophs

  • Definition: Organisms that make their own energy.
  • Method: Using solar energy.
  • Example: Cyanobacteria.

Chemotrophs

  • Definition: Organisms that make their own energy using chemical energy.
  • Examples:
    • Archaea bacteria
      • Pyrococcus sp. (sulfur-dependent archaebacterium)
      • Halococcus sp.
      • Methanogen (stomach of ruminant)

Heterotrophs

  • Definition: Organisms that obtain food by eating.
  • Example: Escherichia coli.

Bacteria Respiration

  • Obligate Anaerobes: Live without oxygen.
  • Facultative Anaerobes: Can live with or without oxygen.
  • Obligate Aerobes: Cannot live without oxygen.

Bacteria Reproduction

  • Binary fission: Asexual reproduction.
  • Conjugation: Sexual reproduction.
  • Spore formation: Formation of endospores.

Binary Fission

  • Process:
    • Cell copies its genetic information.
    • Cell splits into two identical daughter cells.
  • Steps:
    • Duplication of the chromosome.
    • Continued growth of the cell.
    • Division into two cells.

Conjugation

  • Type: Sexual reproduction in bacteria.
  • Process: Two organisms swap genetic information, such as resistance to penicillin.

Spore Formation: Endospore

  • Definition: A type of dormant cell.
  • Characteristics: Exhibits no signs of life.
  • Resistance: Highly resistant to environmental stresses.
    • High temperatures
    • Irradiation
    • Strong acids
    • Disinfectants
  • Formation: Formed by vegetative cells in response to environmental signals indicating a limiting factor for vegetative growth, such as exhaustion of an essential nutrient.

Symbiosis

  • Definition: Close relationship between two species where at least one benefits from the other.
  • Duration: Live together for life.

Parasitism

  • Effect: Bacteria exploit the host cell, causing injury.
  • Result: Causes diseases.
  • Example: Mycobacterium tuberculosis that causes tuberculosis (TB).

Mutualism

  • Definition: Symbiosis in which two species live together in such a way that both benefit from the relationship.
  • Example: Escherichia coli.

Nitrogen Fixation - Mutualism

  • Bacteria: Root nodule bacteria (Rhizobium sp. and Azotobacter sp.) that live in root nodules of legumes (peas, beans, soya beans).
  • Process: Convert atmospheric nitrogen to ammonia, which is absorbed by plants and eventually used to synthesize amino acids.
  • Exchange: In exchange for organic compounds produced by photosynthesis.