Prokaryote Classification Quiz

Prokaryote Classification

• Bacteria and Archaea are the two domains of prokaryotes.
• Bacteria were the first living organisms.
• Archaea evolved in a pre-oxygen atmosphere.
• Gram-negative bacteria evolved first, then gram-positive bacteria.
• All archaea are extremophiles and obligate anaerobes.
• Bacteria can be aerobic or anaerobic.
• Bacteria have a wider range of environmental niches.
• Archaea, unlike bacteria, are non-pathogenic.

Bacterial Shapes and Arrangements

• Major Bacterial Groups:
  • Bacteroides: Gram-negative rods, obligate anaerobes.
  • Photosynthetic Bacteria:
    • Anoxygenic: Sulfur/non-sulfur (purple/green), use an electron donor that is not water.
    • Cyanobacteria: Oxygenic, use water as an electron donor and produce oxygen.
  • Spirochetes: Coiled, move via axial filaments (endoflagella), many are pathogenic.
  • Chlamydias: Intracellular parasitic bacteria.
  • Gram-Positive Bacteria: Latest evolving bacteria, divided into the Firmicutes and Actinobacteria phyla.

Non-Proteobacteria

• Bacteroides:

  • Bacteroides fragilis: Gram-negative rod, obligate anaerobe, normal colon microbiota.
  • First bacteria to evolve.
  • Major inhabitants of the human colon.
  • Ferment indigestible sugar derivatives.
  • Break down toxins.
  • Produce communication molecules (polysaccharide A) that direct the innate immune response.

• Photosynthetic Bacteria:

  • Anoxygenic: Carry out photosynthesis using a non-water electron donor.
  • Purple Sulfur Bacteria:
    • Use H2S as the electron donor.
    • Produce sulfides instead of oxygen.
    • Absorb higher energy wavelengths than green sulfur bacteria.
  • Purple Non-Sulfur Bacteria:
    • Use organic hydrogen sources as the electron donor.
    • Absorb higher energy wavelengths than green non-sulfur bacteria.
  • Green Sulfur Bacteria:
    • Use H2S as the electron donor for photosynthesis.
    • Produce sulfides instead of oxygen.
    • Aerotolerant anaerobes.
    • Absorb light at lower wavelengths than purple sulfur bacteria.
  • Green Non-Sulfur Bacteria:
    • Use organic hydrogen sources as the electron donor.
    • Aerotolerant anaerobes.
    • Absorb lower wavelengths than purple non-sulfur bacteria.

• Spirochetes:

  • Spiral-shaped bacteria.
  • Coiled and move via axial filaments.
  • Many are pathogenic:
    • Treponema pallidum: Causes syphilis.
    • Treponema pertenue: Causes yaws.
    • Treponema pallidum subspecies endemicum: Causes bejel.
  • Can literally "drill" through skin and tissues.

• Chlamydia:

  • Obligate intracellular parasites.
  • Diminished or no cell wall.
  • Grow intracellularly.
  • Elementary Bodies: The "endospore-like" infective form.
  • Reticulate Bodies: The intracellular replicative, cellular form.
  • Chlamydia trachomatis: Causes pelvic inflammatory disease and urethritis.
  • Chlamydophila psittaci: Causes respiratory psittacosis (pneumonia).

Proteobacteria

• All gram-negative bacteria.
• Oxygen-tolerant.
• Most are obligate aerobes or facultative anaerobes.
• Great diversity (over 30% of known bacteria).
• The largest bacterial phyla.
• Diverse metabolisms, including heterotrophs, lithotrophs, and photosynthesizers.
• Five classes: alpha, beta, gamma, delta, epsilon.
• Include oxygenic and anoxygenic photosynthetic bacteria:
  • Cyanobacteria: Oxygenic, use water as the electron donor and produce oxygen.
  • Green Sulfur/Non-Sulfur Bacteria: Anoxygenic, use a non-water electron donor.
• Many pathogenic species (Shigella, Salmonella).
• Contain nitrogen-fixing species.

Cyanobacteria

• Also known as "blue-green algae."
• Oxygenic photosynthetic bacteria.
• Use water as the electron donor and produce oxygen.
• Fix the majority of carbon dioxide in the ecosystem.
• Many contain heterocysts that fix nitrogen.
• Many contain gas vesicles that provide buoyancy.
• Can be unicellular or filamentous, and colonial.

Enterobacteriaceae

• A family of enteric (gut) gram-negative rods.
• All are facultative anaerobes and motile.
• E. coli, an example, uses actin-like filaments to propel itself through host cytoplasm and invade neighboring cells.

Gram-Positive Bacteria: Firmicutes

• Low "GC content" gram-positive bacteria.

• Streptococcus:

  • Coccus in chains.
  • Produce enzymes that destroy tissues.
  • Pathogenic streptococci include:
    • Streptococcus pneumoniae: Causes pneumonia.
    • Streptococcus mutans: Causes dental caries.
  • Beta-hemolytic streptococci hemolyze blood.
    • Streptococcus pyogenes: Causes strep throat and scarlet fever.

• Staphylococcus:

  • Grape-like clusters.
  • Often antibiotic-resistant.
  • Staphylococcus aureus: Causes wound and skin infections, produces four types of toxins:
    • Hemolysin: Lyses red blood cells.
    • Leukotoxin: Lyses white blood cells.
    • Enterotoxin: Intestinal toxin.
    • Toxic-shock syndrome toxin-1: Can cause sepsis.
  • Species of Enterococcus, Streptococcus, and Staphylococcus are distinguished by their level of hemolysis on blood agar plates.

Gram-Positive Bacteria: Actinobacteria

• High "GC content" gram-positive bacteria.

• A broad group, including antibiotic producers, decomposers, and pathogens.

• Cell wall includes unusual cell wall lipids, such as mycolic acid.

• Most stain with acid-fast stain.

• Corynebacterium:

  • Corynebacterium diphtheriae: Causes diphtheria, characterized by difficulty breathing, heart failure, and paralysis.

• Propionibacterium:

  • Produces propionic acid.
  • Propionibacterium acnes: Causes acne.

• Gardnerella:

  • Gardnerella vaginalis: Causes vaginitis.

• Streptomyces:

  • The largest genus of Actinobacteria.
  • Most produce endospores.
  • Isolated from soil.
  • Produce the majority of antibiotics.

• Mycobacterium:

  • Acid-fast bacteria.
  • Mycobacterium tuberculosis:
    • Mycolic acid cell wall: Makes it an intracellular pathogen.
    • Highly infective obligate aerobe: Infects the lungs.
    • Highly contagious: Spread through aerosol transmission.
    • Many infections are antibiotic resistant.
  • Mycobacterium leprae:
    • Mycolic acid cell wall: Makes it an intracellular pathogen.
    • Causes leprosy: Infects peripheral nerves.
    • Targets skin, eyes, nose, and mouth.
    • Not highly contagious: Spread through direct contact.

Archaea

• Often referred to as "extreme bacteria," all are anaerobic extremophiles.
• Unique cell wall: Pseudomurein, which lacks peptidoglycan.
• Heterotrophic: Require organic and inorganic carbon for metabolism.
• Non-pathogenic: No species has been shown to cause human disease.
• Environmental niche: Extreme environments, including the human gut.
• Extremophiles:
  • Extreme Halophiles: Require a salt concentration of over 25%.
  • Thermophiles: Require a growth temperature over 80°C.
  • Psychrophiles: Require low temperatures.

Test your knowledge about the two domains of prokaryotes: Bacteria and Archaea. Explore the evolution, characteristics, and classification of various bacterial groups and their distinctive features. This quiz covers topics such as bacterial shapes, arrangements, and metabolic types.