Chapter 28: Prokaryotes

Chapter 28: Prokaryotes

1. Vibrio cholerae

   • Vibrio cholerae was the cause of the 2010 cholera outbreak in Haiti that caused the death of an estimated 10000 people. They believe the disease was brought over by the UN peacemakers who had been stationed in Nepal.
   • How cholerae affects the body
     • How it spreads: cholera gets in through contaminated food or water. The bacteria gets in through your stomach and into your large intestine where it multiplies rapidly. The toxin prevents the intestine from absorbing water from digested food causing diarrhea and dehydration. Treatment: cholera is treated with salt solution, intravenous fluids, or antibiotics
   • John Snow
     • John Snow was able to identify the source of a cholera outbreak in Soho London in 1854. He plotted sources of drinking water and cholera outbreaks on a map (he became famous for introducing spatial statistics)from which he determined a link. He was able to identify a single fountain as the source of the outbreak. Removing the handle from the fountain ended the outbreak Before this, people adhered to the miasma theory which said that diseases were caused by bad air.

2. Historic advances in microbiology

   • Antony van Leeuwenhoeck
     • Antony van Leeuwenhock was the first to observe and accurately describe microbial life. He described his first microbe in 1670. He made important advances in microscopes.
     • Robert Hooke
       • Robert Hooke was the first person to identify cells as the fundamental unit of life
       • Louis Pasteur
         • Louis Pasteur, in 1859, refuted the idea that microorganisms arise spontaneously with his experiment. In his experiment, he saw that microbial growth is inhibited when the boiled sample is left sealed, but when broken and exposed to air, the sample becomes contaminated.
         • Robert Koch
           • Robert Koch studied anthrax in detail and cultured the causative agent. From that, he determined the germ theory of diseases.
           • Germ Theory of Diseases
             • 1. Microbe must be present in every case of the disease and absent in healthy individuals 2. Microbe must be able to be isolated and grown in pure culture 3. The same disease must occur when microbe is used to infect a healthy host 4. The same microbe must be able to be isolated again from disease

3. Characteristics of Prokaryotes

   • Unicellular
     • With rare exceptions, all prokaryotes are single-celled
     • Cell size
       • Prokaryote cell size vary tremendously, but most are less than 1 micrometer in diameter..
       • Nucleoid
         • Instead of a nucleus, prokaryotes have a single circular chromosome (cholera has two) and they also have plasmids
         • Cell division
           • Cell division in prokaryotes is done by binary fission. Prokaryotes can also exchange genetic material via horizontal gene transfer.
           • Internal compartmentalization
             • Prokaryotes don't have membrane-bound organelles (which is what makes them prokaryotes). The plasma membrane has been extensively infolded.
             • Flagella
               • Prokaryotes have spin-like propellers that help them move around. These are different from eukaryotic flagella which are more whip-like
               • Metabolism
                 • Prokaryotes use energy stored in inorganic molecules to synthesize carbohydrates
                 • Chemoheterotrophs
                   • Energy and carbon obtained from organic molecules
                   • Photoautotrophs
                     • Energy and carbon obtained from sunlight
                     • Chemolithoautotrophs
                       • Energy is obtained from inorganic materials
                       • Photoheterotrophs
                         • Energy is obtained from sunlight and carbon is obtained from organic molecules
   • Reproduction
     • Binary fission
       • In binary fission, a single, circular chromosome divides creating two identical copies of the chromosome.
       • Horizontal gene transfer
         • Conjugation
           • Conjugation is the transfer of DNA from one bacterial cell to another
           • Transduction
             • Transduction is when DNA is incorporated from bacteriophages
             • Transformation
               • In transformation, DNA is obtained directly from the environment

4. Cell structure of Prokaryotes

   • Prokaryotes have three basic forms: rods, cocci, and spirals
   • S-layer
     • This is found in a prokaryote's cell wall. It is a rigid paracrystalline layer outside the peptodoglycan found in some bacteria and archaes. It has diverse functions.
     • Capsule
       • Prokaryotes have this gelatinous layer that aids in attachment and protects the organism.
       • Endospore
         • A thick wall around the bacteria's genome and a small portion of the cytoplasm. Formation of the endospore happens when the bacteria is under stress. Endospores are highly resistant to environmental stress, especially heat. When conditions improve they can germinate and return to normal cell division. 
         • Plasmids
           • Plasmids encode functions that may be advantageous for the organism. The best known plasmids are F plasmids in e. coli
   • Gram positive vs. Gram negative
     • Gram positive bacteria have a thicker peptidoglycan wall and stain a purple color, while gram negative bacteria contain less peptodyglycan and do not retain the purple dye. 

5. Bacteria vs. Archaea

   • Plasma membrane
     • They have plasma membranes with a fluid mosaic architecture, but archaea have membrane lipids composed of glycerol linked to hydrocarbon chains
     • Cell wall
       • Bacterial cell walls contain peptidoglycan, while archael cell walls do not. (Archae has pseudomurein, which is made with different carbohydrates)
       • DNA Replication
         • Replication has the same origin for both, but archaea's initiation stage is similar to that of eukaryotes.
         • Gene expression
           • Archaea's gene expression (RNA polymerase and translational machinery) is more similar to eukaryotes.

6. Prokaryotes are challenging to classify

   • Historically, simple descriptive traits were used: Gram positive or gram negative Photosynthetic or non-photosynthetic Motile or non-motile Colony formation and morphology Spore formation Importance to humans Molecular approaches include analysis of amino acid sequences, nucleic acid hybridization, gene and RNA sequencing, whole-genome sequencing and analysis of acid-base sequences

7. Good bacteria vs. Bad bacteria

   • Yersinia pestis
     • The Bubonic plague aka the Black death was caused by Yersinia pestis. The disease may have killed half of the people living in Europe at the time.
     • Anthrax
       • Anthrax is bacteria in spore form (endospore). When you inhale it, it creates a nice, warm, moist environment for germination Anthrax targets the chest or muscles. It causes the skin to blister, or can even cause ulcers. 
   • E. coli
     • They inhabit the human gut and produce vitamin K2 which is essential for blood clotting and helps keep bad bacteria in check.
     • Lactobacilli
       • Lactobacilli can produce vitamins and nutrients, boost immunity and protect against carcinogens
       • Bacteria involved in cycling important elements
         • Ex. nitogen-fixing prokaryotes