21.2 Bacteria : An overview Bacterial Structure and Reproduction Notes

Bacterial Structure

  • Kingdoms: Bacteria includes organisms from the Kingdoms Eubacteria and Archaea.

  • Differences from Eukaryotes (7 characteristics):

    1. Internal Compartmentalization:
      • Bacteria are prokaryotes: they lack a cell nucleus.
      • Many have no internal compartments or membrane systems.
    2. Cell Size:
      • Smaller than eukaryotic cells: typically 1-5 micrometers (\mum).
      • Some bacteria can be as large as 750 \mu m, and some eukaryotic cells can be very small.
    3. Multicellularity:
      • All bacteria are single-celled.
      • Some may stick together or form strands but lack specialized cell functions.
    4. Chromosomes:
      • Single, circular piece of DNA.
      • Eukaryotes have linear DNA.
    5. Reproduction:
      • Bacteria reproduce through binary fission (one cell divides into two).
      • Eukaryotic cell division involves microtubules pulling chromosomes to opposite poles.
    6. Flagella:
      • Bacterial flagella consist of a single fiber of protein that spins like a corkscrew.
      • Pili: Short, thick outgrowths that enable bacteria to attach to other cells or surfaces.
    7. Metabolic Diversity:
      • Bacteria can perform many metabolic processes eukaryotes cannot: example: aerobic and anaerobic processes.

Bacterial Cell Shapes

  • Basic Shapes:
    • Rod-shaped: bacillus.
    • Spiral: spirillum.
    • Round: coccus.
  • Aggregations:
    • Strands/filaments: prefix strepto-.
    • Clusters: prefix staphylo-.

Cell Walls and Exterior Structures

  • Cell Wall: Made of peptidoglycan.
  • Capsule:
    • Gel-like layer outside the cell wall and membrane (in Eubacteria).
  • Gram Staining:
    • Eubacteria have either Gram-negative or Gram-positive cell walls, differentiated by Gram staining.
    • Integral for determining how bacteria respond to antibiotics.
    • Antibiotics are drugs or chemicals that alter the life processes in bacteria.
  • Endospores:
    • Formed during harsh conditions (high temperatures, drought).
    • Thick-walled structures that protect chromosomes and cytoplasm.
    • Can germinate years later to allow new bacterial growth.
  • Pili:
    • Enable bacteria to attach to other cells or surfaces (e.g., human skin).
    • Facilitate conjugation: exchange of genetic material between two organisms.
    • Allows gene transfer within a bacterial population.

Obtaining Energy

  • Diverse Habitats: Bacteria are found in almost every kind of habitat.

  • Categorization by Energy Source:

    • According to their methods of obtaining energy or according to their phylogenetic relationships.

  • Photosynthesizers:

    • Four types: green sulfur, purple nonsulfur, purple sulfur, and cyanobacteria.
    • Purple sulfur and green sulfur bacteria: anaerobic environments, use sulfur compounds (e.g., hydrogen sulfide) for photosynthesis.
    • Purple nonsulfur bacteria: depend on organic compounds (carbohydrates, acids) as a source of electrons.
    • Cyanobacteria: form large mats of filaments, responsible for Earth's oxygen atmosphere; fix nitrogen (e.g., Anabaena).

  • Chemoautotrophs:

    • Obtain energy by removing electrons from inorganic molecules (ammonia, hydrogen sulfide).
    • Manufacture their own proteins and amino acids.
    • Examples: Nitrosomonas and Nitrobacter (involved in nitrification).

  • Heterotrophs:

    • The majority of bacteria are heterotrophs.
    • Many are aerobic (live in the presence of oxygen).
    • Principal decomposers.
    • Examples: Staphylococcus (food poisoning) and Rhizobium (nitrogen fixation in legume roots).
    • Farmers rotate crops, planting legumes to increase soil fertility.

Pathogenic Bacteria

  • Competition for Resources: Bacteria compete with the body for vitamins, minerals, proteins, carbohydrates, and fats.
  • Metabolizing Host Tissues:
    • Heterotrophic bacteria can metabolize body tissues, causing health problems.
    • Example: Mycobacterium tuberculosis uses lung tissue as nutrients, causing tuberculosis.
      • Symptoms: chest pains, weight loss, fatigue, coughing up blood/sputum, loss of appetite.
      • TB can be fatal within 18 months to 5 years.
    • Propionibacterium acnes: causes acne by metabolizing oil in skin glands, increasing oil and bacterial populations in pores during puberty, forming pimples and blackheads.

Bacterial Toxins

  • Secreting Toxins: Bacteria cause diseases by secreting toxins or into food.
  • Staphylococcus aureus: causes food poisoning.
  • Clostridium botulinum: endospore-forming bacteria that produces a deadly toxin, causing a fatal nerve disease (botulism).
    • Occurs in improperly canned food.
    • Symptoms: paralysis, double vision, breathing complications.
  • E. coli: Normally lives in intestines, but some strains acquire toxin-coding DNA through conjugation.
    • Common in raw or poorly cooked meat.
  • Prevention: Hygiene practices such as boiling water, washing utensils in hot soapy water, and using antibacterial products.

Biowarfare

  • Definition: Intentional exposure of people to biological toxins or pathogens (bacteria, viruses).
  • The US government is constantly alert to any likelihood that its citizens or military personnel may be exposed to biological toxins or pathogens

Antibiotics

  • Discovery: Alexander Fleming discovered penicillin in 1928 (from Penicillium fungus).
    • S. aureus could not grow near the fungus.
  • Uses: By the 1940s, penicillin was used to treat bacterial diseases like pneumonia.
  • Other Antibiotics: Ampicillin and tetracycline have since been developed/discovered.

Antibiotic Resistance

  • Emergence: Concerns over antibiotic-resistant bacteria.
  • Mechanism: Bacteria mutate and replicate rapidly, producing resistant bacteria.
  • Antibiotic Misuse:
    • Stopping antibiotics prematurely allows the most resistant bacteria to survive, leading to stronger bacteria and possible reinfection.
  • Multiple Antibiotic Resistance:
    • Concerns over administering multiple antibiotics simultaneously.
  • Antibacterial Soaps:
    • Potential to favor antibacterial resistance.

Importance of Bacteria

  • Food and Chemical Production:
    • Fermented foods: buttermilk, vinegar, sourdough bread, pickles, cheese, sauerkraut.
    • Chemicals: Clostridium produces acetone and butanol for industrial use.
    • Genetic engineering: produce drugs and complex chemicals for research.
  • Mining:
    • Concentrate desired elements from low-grade ore.
    • Chemoautotrophic bacteria convert sulfur into soluble compounds, leaving desired mineral behind (e.g., copper, uranium).
  • Environmental Uses:
    • Metabolize organic compounds: clean up oil and chemical spills.