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!