Notes on Prokaryotic Life and Their Characteristics

Definition: Prokaryotes are unicellular organisms without a nucleus.
Size: Generally smaller than eukaryotic cells.
Biomass: The collective biomass of prokaryotes is significantly greater than that of all eukaryotes (at least 10 times more).
Environmental and Health Impact: Prokaryotes have significant effects on the environment and our health, living in and on the human body in greater numbers than eukaryotic cells.

Domains: Classified into two primary domains:
- Archaea: Often found in extreme environments.
- Bacteria: More diverse and includes pathogens.

Structure:
- Unicellular.
- No membrane-bound organelles or cytoskeleton.
Morphology: Common shapes include:
- Cocci: Spherical.
- Bacilli: Rod-shaped.
- Spirilla: Spiral-shaped (short and rigid) & spirochetes (long and flexible).
- Vibrio: Comma-shaped cells.
Cell Wall: Composed of peptidoglycan in bacteria, absent in archaea, essential for maintaining shape:
- Gram-Positive: Thick peptidoglycan layer.
- Gram-Negative: Thinner peptidoglycan and outer membrane.

Capsules: For protection and attachment.
Fimbriae: Used for attachment to surfaces.
Flagella: For locomotion, which can be powered by various mechanisms, including a gliding motion.

Asexual Reproduction: Primarily through binary fission.
Genetic Recombination:
- Transformation: Uptake of foreign DNA.
- Conjugation: Direct transfer of DNA between cells; often involves mating bridges.
- Transduction: Transfer of DNA through viruses.
Endospores: Allow survival in harsh conditions, can remain dormant for years to thousands of years.

Energy Sources: Can be phototrophic (using light) or chemotrophic (using chemicals).
Modes of Nutrition:
- Photoautotrophs: Use light and CO2 (e.g., cyanobacteria).
- Chemoautotrophs: Use inorganic compounds.
- Photoheterotrophs: Use light and organic compounds.
- Chemoheterotrophs: Use organic compounds for both energy and carbon.

Nitrogen Metabolism:
- Nitrogen Fixation: Conversion of N2 to forms usable by plants (e.g., ammonia).
- Ammonification: N2 → NH4+.
- Nitrification: NH4+ to NO2- to NO3-.
- Denitrification: Conversion of nitrates back to N2 gas, thus returning nitrogen to the atmosphere.

Biofilms: Complex communities of microbes that adhere to surfaces, which can be difficult to eradicate due to their protective layers.
Bioremediation: Use of prokaryotes to clean up the environment, e.g., wastewater treatment facilities.

Subgroups:
- Proteobacteria: Diverse and often gram-negative.
- Cyanobacteria: Only prokaryotes capable of oxygenic photosynthesis.
- Chlamydias: Intracellular pathogens without peptidoglycan walls.
- Spirochetes: Notable for diseases like syphilis.
- Gram-positive bacteria: Include those producing antibiotics and endospores.

Characteristics: Thrive in extreme environments; categorized into:
- Extreme Halophiles: Tolerate or require high salinity.
- Extreme Thermophiles: Thrive at high temperatures (60-80°C).
- Methanogens: Produce methane in anaerobic conditions.

Play an essential role in recycling elements, decomposition of organic matter, and nitrogen fixation, contributing significantly to the health of ecosystems.

Types of Symbiosis:
- Mutualism: Both organisms benefit.
- Commensalism: One benefits, the other is unaffected.
- Parasitism: One benefits at the expense of the other (pathogens).

Rapid evolution of antibiotic resistance has become a significant concern in healthcare, with many bacteria developing resistance quickly, outpacing the development of new treatments.