Prokaryotes

Introduction to Prokaryotes

  • Prokaryotes are organisms in the domains Bacteria and Archaea.

  • They first appeared on Earth 3.5 to 3.8 billion years ago and are found in diverse environments.

Microbial Mats and Stromatolites

  • Microbial mats, formed by prokaryotes, are among Earth’s earliest life forms.

  • Stromatolites are fossilized microbial mats, significant as the oldest records of life.

Earth's Atmosphere and Cyanobacteria

  • Earth's early atmosphere was anoxic, supporting anaerobic organisms.

  • Cyanobacteria evolved from phototrophs and contributed to oxygenating the atmosphere, enabling terrestrial life.

Extremophiles

  • Extremophiles thrive under extreme conditions, such as:

    • Acidophiles (pH < 3)

    • Alkaliphiles (pH > 9)

    • Thermophiles (60-80 °C)

    • Halophiles (high salt concentration)

Prokaryotic Growth and Culturing

  • Over 99% of prokaryotes cannot be cultured in the lab due to unknown growth requirements.

  • Biofilms are microbial communities that enhance resistance to destruction.

Prokaryote Shapes and Structure

  • Prokaryotes come in three shapes: cocci (spherical), bacilli (rod-shaped), spirilli (spiral-shaped).

  • They lack a nucleus and have single circular DNA, usually enclosed by a cell wall.

Reproduction and Gene Transfer in Prokaryotes

  • Prokaryotes reproduce asexually via binary fission.

  • Genetic variation can occur through transformation, transduction, and conjugation.

Differences Between Bacteria and Archaea

  • Bacteria have peptidoglycan in their cell walls; Archaea do not.

  • Archaeal membranes contain ether-linked lipids that differ from bacterial phospholipids.

Prokaryotes in Nutrient Cycles

  • Prokaryotes are crucial to the carbon and nitrogen cycles, facilitating processes like nitrogen fixation and organic carbon cycling.

Disease Implications of Prokaryotes

  • Prokaryotes can cause epidemics; biofilms contribute to chronic infections that resist treatment.

  • Antibiotic overuse has led to the emergence of resistant "superbugs."

Benefits of Prokaryotes

  • Prokaryotes perform essential functions such as nitrogen fixation and bioremediation, and impact human health via the microbiome.