Prokaryotes

Chapter 27: Prokaryotes

27.1 Prokaryotic Diversity

  • Prokaryotes are the oldest and most abundant forms of life.
  • Exist for over a billion years before eukaryotes.
  • Vast diversity with 90-99% still unknown and undescribed.
  • Classified into:
  • Bacteria
  • Archaea (many are extremophiles)

27.2 Prokaryotic Cell Structure

  • Basic Shapes of Prokaryotic Cells:

  • Bacillus: rod-shaped

  • Coccus: spherical

  • Spirillum: helical-shaped

  • Cell Wall Structure:

  • Peptidoglycan forms a rigid network maintaining cell shape.

  • Gram-positive bacteria:

    • Thick peptidoglycan layer, stains purple.
    • Contains lipoteichoic and teichoic acids.

  • Gram-negative bacteria:

    • Thin peptidoglycan layer, retains counterstain, appears pink.
    • Contains an outer membrane with lipopolysaccharides, more resistant to antibiotics.

27.3 Prokaryotic Genetics

  • Genetic Composition:

  • Chromosome: a single, circular double-stranded DNA.

  • Plasmids: small circular DNA molecules that can confer advantageous traits.

  • Cell Division and Genetic Recombination:

  • Most prokaryotes divide by binary fission.

  • Genetic material exchange via horizontal gene transfer (HGT), which is not a form of reproduction.

27.4 The Metabolic Diversity of Prokaryotes

  • Various metabolic pathways:
  • Oxygenic Photosynthesis: conversion of solar energy to chemical energy using water.
  • Anoxygenic Photosynthesis: using other compounds instead of water.
  • Chemolithotrophy: energy derived from oxidation of inorganic compounds.

27.5 Microbial Ecology

  • Prokaryotes play crucial roles in ecosystems:
  • Decomposition of organic matter
  • Nutrient recycling
  • Symbiotic relationships in gut microbiota are essential for host health.

27.6 Bacterial Diseases of Humans

  • Pathogen Mechanisms:

  • Gain entry, colonize, evade the immune system, spread, and damage the host through toxins.

  • Major Diseases:

  1. Anthrax caused by Bacillus anthracis - found in livestock, can be fatal.
  2. Cholera caused by Vibrio cholerae - leads to severe diarrhea and dehydration.
  3. Gonorrhea caused by Neisseria gonorrhoeae - a common STI.
  4. Syphilis caused by Treponema pallidum - progresses through four stages.
  5. Chlamydia becomes asymptomatic but can lead to serious reproductive health issues.

Historical Context in Microbiology

  • Key Contributors:
  • Giovanni Fracastoro (1546): Suggested unseen organisms cause disease.
  • Robert Hooke (1665): First to observe cells.
  • Antonie van Leeuwenhoek (1676): Observed living cells and bacteria, called them "animalcules".
  • Louis Pasteur (1861): Disproved spontaneous generation, established germ theory.
  • Robert Koch: Developed postulates for identifying disease-causing organisms, pivotal in bacteriology.

Biofilms in Prokaryotic Life

  • Complex microbial communities embedded in a self-produced matrix.
  • Can be beneficial (e.g., wastewater treatment) or harmful (infections).

Probiotics and Prebiotics

  • Probiotics: Beneficial live microorganisms that support gut health.
  • Prebiotics: Non-digestible food components that promote the growth of beneficial bacteria.

Gut Microbiota and Health

  • Over 39 trillion bacteria in the human body, predominantly in the gut.
  • Essential for digestive health, major immune functions occur in the gut.

Conclusion

  • Prokaryotes have a rich history and significant roles in health, disease, and ecological balance. Understanding their structure, genetics, and their interactions within environments and hosts is crucial for advancements in microbiology and medicine.