Prokaryotes

Prokaryotes

Overview

  • Prokaryotes are discussed in Chapter 22.
  • Examples include halophiles, methanophiles, Bacillus, Actinobacteria, Spirochaetes, and Thermophiles.
  • Three domains of life: Eukaryota, Archaea, and Bacteria.
  • Eukaryota includes animals, green plants, and fungi.

Characteristics of Prokaryotes

  • First inhabitants of Earth, appearing 3.5 - 3.8 billion years ago.
  • Single-celled organisms.
  • Lack a defined nucleus.
  • Lack some other organelles.
  • Inhabit extreme environments (hot, cold, wet, dry, high pressure, zero oxygen).
  • Live on or in virtually every living thing on Earth.

Prokaryotic Diversity (22.1)

  • Earth is approximately 4.5 billion years old.
  • Prokaryotes appeared approximately 3.8 billion years ago.
  • Early Earth conditions: strong solar radiation, strong volcanic activity, anoxic atmosphere, leading to lots of mutations.
  • Phototrophs appeared approximately 3.5 billion years ago.
  • Cyanobacteria appeared 2.5 billion years ago and began oxygenation of the atmosphere.
  • Oxygenation led to the formation of the ozone layer (O_3), allowing more complex life forms to arise.

Microbial Mats/Biofilms

  • Multi-layered sheet of prokaryotes, mostly bacteria, and some archaeans.
  • Fossil evidence dates back 3.5 billion years.
  • Likely obtained energy from hydrothermal vents until the evolution of photosynthesis.
  • Only a few centimeters thick.
  • Exist where different types of materials meet.

Stromatolites

  • Fossilized remains of microbial mats.
  • Sedimentary structures formed by prokaryotes in microbial mats precipitating minerals out of the water.
  • Still being formed in some places on Earth.

Adaptations to Extreme Environments

  • Prokaryotes are adapted to survive extreme environments with a protective cell wall.
  • Extremophiles:
    • Adapted to survive in harsh environments.
    • Cannot survive in moderate environments.
  • Extremophile conditions for optimal growth:
    • Acidophiles: pH 3 or below
    • Alkaliphiles: pH 9 or above
    • Thermophiles: Temperature 60–80 °C (140–176 °F)
    • Hyperthermophiles: Temperature 80–122 °C (176–250 °F)
    • Psychrophiles: Temperature of -15-10 °C (5-50 °F) or lower
    • Halophiles: Salt concentration of at least 0.2 M
    • Osmophiles: High sugar concentration

Robert Koch & Culturing Bacteria

  • Robert Koch is credited with discovering techniques for culturing bacteria with assistance from Julius Petri.
  • Koch’s study of tuberculosis bacteria aided in the creation of his postulates for identifying bacteria that cause disease.

Koch’s Postulates

  • An organism can be identified as the cause of disease when it is present in all infected samples and absent in healthy samples.
  • An organism can cause infection even after it has been cultured many times.
  • Can only be applied to organisms that can be isolated and successfully cultured in a laboratory.
  • 99% of bacteria and archaea cannot be grown in a laboratory setting due to various unknowns about their environmental needs

Viable But Not Culturable (VBNC)

  • Culturable organisms can become unculturable under stressful conditions, entering a dormant state as a self-preservation mechanism.
  • Triggers for this state are not well understood.
  • “Resuscitation” occurs when environmental conditions improve.

Biofilms - A Microbial Community

  • Most prokaryotes prefer to live in communities (biofilms) that allow them to interact with other prokaryotic organisms.
  • Biofilms typically grow attached to surfaces and are very robust populations.

Structure of Prokaryotes (22.2)

  • Unicellular.
  • Lack membrane-bound organelles (nucleus, mitochondria, etc.).
  • Contain nucleoid - one circular strand of DNA.
  • Protective cell wall.
  • Some have a capsule to aid in attaching to other cells and avoiding desiccation.
  • Some have flagella for movement.
  • Reproduction is asexual.

Reproduction by Binary Fission

  • Chromosome is duplicated and copies separate from each other.
  • Enlarged prokaryote splits at the middle.
  • Results in 2 identical progeny.
  • Typical method of reproduction.
  • Does not allow for genetic diversity.

Introducing Diversity in Prokaryotes

  • Transformation.
  • Transduction.
  • Conjugation.

Transformation

  • Prokaryote takes in DNA shed by another prokaryotic cell in its environment.
  • Incorporates new DNA sequence into its own.
  • Can cause a non-pathogenic prokaryote to become pathogenic.

Transduction

  • Bacteriophages may move short pieces of DNA from one bacteria to another.
  • Results in a recombinant organism.

Conjugation

  • DNA transfer takes place between prokaryotes via a pilus.
  • Brings the organisms into direct contact with each other.

Bacterial Diseases in Humans (22.4)

Important Vocabulary

  • Pathogen: infectious agents that cause disease.
  • Epidemic: a disease that occurs in unusually high numbers of individuals in a population at the same time.
  • Pandemic: a widespread disease, usually worldwide.
  • Endemic disease: a disease that is always present at low rates in a population.
  • Emerging disease: a disease that appears in a population for the first time.
  • Re-emerging disease: a disease that was once under control but is now increasing in occurrence.
  • Zoonoses: diseases that primarily infect animals but can be transferred to humans.

Pathogen-borne Diseases

  • Affected human populations and their ancestors for millions of years.
  • Only really been studied and understood scientifically in the last few hundred years; previously believed to be spiritual ailments.

The History of Bacterial Disease

  • Bacterial infections have been recorded as far back as 3000 BC in both fossilized remains as well as written records.
  • 430 BC - Plague of Athens
    • Thought to be typhoid fever caused by Salmonella enterica.
    • Killed ¼ of Athenian troops in the Peloponnesian War.
    • Identified by information from DNA in teeth of soldiers from a mass gravesite.

Bubonic Plagues - Attacking the Lymph Nodes

  • Plague of Justinian: 541 - 750 AD
    • Decreased the European population by 50%.
  • The Black Death: 1346 - 1361 AD
    • Caused by Yersinia pestis.
    • Reduced the world’s population from approximately 450 million to approximately 350 million.
    • Struck London again in the 1600s.
  • Spread of this disease (and many others) exacerbated by world travel.
  • Approximately 1,000 - 3,000 cases each year now.

Foodborne Disease

  • Prokaryotes typically impact food in the form of a biofilm.
  • Contamination takes place from food processing equipment or from the food itself.
  • 76 million people get sick from foodborne illness each year.

Biofilms & Disease

  • Biofilms are very difficult to destroy due to their antibiotic resistance.
  • Cause an array of human diseases
    • Otitis Media
    • Legionnaire’s Disease
    • Infections in those with Cystic Fibrosis
  • Colonize medical devices (catheters, orthopedic devices, etc.).
  • 65% of all hospital infections are due to biofilms.

Antibiotics

  • A chemical that is produced either by an organism or synthetically that prevents the growth of another organism.

Beneficial Prokaryotes (22.5)

  • Only a few (relatively) Prokaryotes are harmful.

The Nitrogen Cycle

  • Why is nitrogen important?
    • Essential for nucleic acids and proteins.
    • The building blocks of life.
  • Largest pool of Nitrogen is in the atmosphere.
  • Nitrogen has to be “fixed” into an accessible form.
    • Abiotic fixation (industrial production).
    • Biological Nitrogen Fixation (prokaryotes).

Biological Nitrogen Fixation (BNF)

  • THE MOST IMPORTANT BIOLOGICAL PROCESS ON EARTH!
  • N2 + 16ATP + 8e^- + 8H^+ \rightarrow 2NH3 + 16ADP + 16Pi + H_2
  • Accounts for 65% of the nitrogen used in Agriculture.

Prokaryotes Responsible for BNF

  • Cyanobacteria - aquatic environments.
  • Rhizobia - soil environments
    • Various bacterial species.
  • Symbiotic Nitrogen Fixation
    • Legumes
    • Easy and cheap fertilizer
    • Nitrogen > ammonia
    • Crucial agricultural protein

The Carbon Cycle

  • Decomposers break down decaying organic matter & release Carbon Dioxide through cellular respiration.
  • Photosynthesis.
  • Synthesis of fossil fuels.

Prokaryotes in Biotechnology

  • Biotechnology is the use of biological systems, living organisms, or their byproducts in the production of commercial goods.
  • Humans have been using “biotechnology” well before it had a name.
  • Fermented and cultured foods have existed for approximately 7,000 years.

The Human Microbiome

  • Microorganisms are essential to the functioning of many of our body systems.
  • Now believed to be a 1:1 ratio of your cells to microbial cells in your body.

Microbial Bioremediation

  • The use of prokaryotes in pollution cleanup.
    • Agricultural pollution
    • Toxic metals
    • Oil spills
      • Petroleum-consuming bacteria existed pre-spills.

Up Next

  • Chapter 23… Protists!