I. The Unseen Multitudes
  • Microorganisms are single celled organisms that are too small to see without a microscope.
  • A thousand bacteria would fit side by side on the top of the dot of an 11 pt font "i"
  • Viruses are even smaller than bacteria and are measured in nanometers or billionths of a meter.
  • Bacteria far outnumber and out reproduce all other organisms in all the other kingdoms combined.
  • Under ideal conditions bacteria can divide every 20 minutes. In 10 hrs. a single bacteria could have billions of descendents.
  • Bacterial growth is kept in check by the nutrients avaliable and infecting viruses. Bacteria will use up their resources and pollute their environment to the point of stopping their own reproduction.
  • Some bacteria are pathogens. They alter the tissue and cells they invade and cause disease.
  • Most of the bacteria that exists are beneficial and our world would not exists as we know it without them.
II. Characteristics of Bacteria
  • Many thousands of species live in every environment.
  • The oldest species have been surviving for millions of years 2,780 meters below the surface of the Earth.
  • Bacterial cells in your gut outnumber your body cells.
  • Bacteria have the longest evolutionary history and have the greatest diversity in securing resources.
    • Photoautotrophic Bacteria use sunlight to make sugars
    • Aerobic bacteria must use oxygen to survive and usually live in high oxygen rich environments such as on the surface of objects.
    • Anaerobic bacteria can't use oxygen or may even die in its presence.
    • Facultative Anaerobes usually don't use oxygen but can in some cases.
    • Chemoautotropic bacteria use organic compounds as a source of electrons to make sugars
    • Chemolithotrophs use inorganic substances such as sulfur, nitrogen, or a form or iron
    • Photoheterotrophic bacteria use photosynthesis to create sugars, but have to use fatty acids or complex carbohydrates which other organisms produce as a source of carbon instead of carbon dioxide.
    • Chemoheterotrophic bacteria are either parasites or saprobes. Parasites live on or in a living host. Where a saprobes obtain nutrients from products, wastes, or remains of other organisms.bv 2.png
  • Size and Shapes - three basic shapes are common and two types of growth patterns
    • coccus - spherical
    • bacillus - rod shaped
    • spirillum - contains one or more twists
    • staph - bacteria grow in clumps or clusters like grapes
    • strep - bacteria grow in chains or strings
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  • Structural Features
    • Bacteria are prokaryotic (contain no nucleus or membrane bound organelles)
    • Reactions take place in the cytoplasm or along the cell membrane
    • There is usually a cell wall made of peptidoglycan which is made of peptide groups that link many polysaccharides together.
    • Bacteria can be identified as either Gram + or Gram -. This staining technique utilizes the difference in cell wall structure.bv 4.png
    • Many times bacteria contains a glycocalyx which is a sticky mesh. When this mesh is highly organized it is called a capsule. Less organized it is known as a slime layer. The glycocalyx helps bacteria adhere to surfaces such as teeth and underwater rocks.
    • Bacteria use flagella as a structure of motility in a propeller type motion.
    • Pili are short proteins that project above the cell wall and help the bacteria adhere to surfaces, one another, and is used during conjugation.
II. Bacterial Growth and Reproduction
  • The Nature of Bacterial Growth
    • We measure bacterial growth as an increase in the number of cells in a given population. Under ideal conditions each bacteria gives rise to two daughter cells.
    • Each bacterial species grow and reproduce in their own optimal environment. What causes increased growth for one type of bacteria might be lethal to another.
  • Prokaryotic Fission
    • When a bacteria reaches twice its original size it divided and each daughter cell receives a single bacterial chromosome. This is circular and double stranded DNA. The creation of a daughter cell is accomplished by a process of fission.
      • DNA is replicated and the two resulting strands are attached to the plasma membrane at points right next to each other.
      • The membrane between the two strands is increased until the two strands are separated.
      • The two strands are then divided by a growing cell wall and cell membrane until there are two genetically equivalent daughter cells.
  • Bacterial Conjugation
    • Daughter cells may also inherit one ore more plasmids which is a small self-replicating circle of extra DNA that contains a few genes.
    • Some bacteria have the ability to engage in bacterial conjugation because of these genes located on some plasmids.
    • This mechanisms allows a donor cell to transfer plasmid DNA to a recipient cell. A conjugation tube develops between two cells and after this plasmid DNA is transferred through the tube.bv 5.png
III. Bacterial Classification
  • Before the techniques of RNA hybridization and DNA analysis bacteria were classified on how many traits they share such as cell shape, motility, staining attributes of the cell wall, nutritional requirements, metabolic patterns, and the presence of absence of endospores.
  • With the analysis of RNA and DNA, groups that were thought to be unrelated are now showing connections.
  • The major divergence between bacteria is seen in the creation of eubacteria and archaebacteria.
IV. Eubacteria
  • Most of the bacteria that are known are Eubacteria. All of these bacteria have fatty acids incorporated into their plasma membranes and peptidoglycan in their cell walls. This kingdom is huge and extremely diverse.
  • A Sampling based on Nutrition
    • Photoautotrophic Eubacteria
      • Cyanobacteria (aka. blue-green algae) are a great example and are among the most common photoautotrophs on Earth. Most live in ponds and other freshwater habitats and can grow in slimy dense mats on the top of nutrient rich water.
      • Anabaena and other types convert nitrogen gas to ammonia. Sometimes these become heterocysts which can make a nitrogen-fixing enzyme that is then shared with photosynthesizing cells and in return get carbohydrates.
      • Anaerobic photoautotrophs such as green bacteria get electrons from hyddrogen sulfide or hydrogen gas instead of from water.
    • Chemoautotrophc Eubacteria
      • many bacteria in this category are vital to the cycling of nitrogen, sulfur and other nutrients through ecosystems. These are seen in the soil and fix nitrogen into a form that plants can take up through their roots.
    • Chemoheterotrophic Eubacteria
      • Most bacteria fall into this category. Some are decomposers and can even break down pesticides in soil.
      • Lactobacillus is used in the production of pickles, sauerkraut, buttermilk, and yogurt and helps in digestion. Actinomycetes is the source of antibiotics. E. coli
        produces vitamin K and lives in human intestines and breaks down fats and prevents many pathogenic bacteria from growing.
      • Azospirillum is a bacteria that helps sugarcane and corn fix nitrogen and beans, peas, and other legumes have a symbiotic relationship and culture the bacteria Rhizobium in nodules in their roots.
      • Pathogenic strains are also found in this catagory such as pseudomonads which can transfer antibiotic-resistance genes on plasmids. Some strains of E.coli cause food poisoning. Clostridium botulinum is responsible for the toxins that cause botulism which can paralyze and cause death. C.tetani which is a relative to C. botulinum causes the disease tetanus. This bacteria lives in the soil and has the ability to form endospores. Endospores are structures that form around the DNA and some cytoplasm when there is a depletion of a vital nutrient that stops cell growth. These are exceptionally resistant to heat, drought, irradiation, acids, disinfectants, and boiling. They can remain dormant, sometimes for decades. When conditions are again favorable to growth they will generate a single bacterial cell.bv 7.png
      • These chemoautotrophic eubacteria are also transferred from one host to another such as from insect to human as seen in the bacteria Borrelia burgdorferi which causes Lyme disease from a tick bite.bv 6.png
  • The "Simple" Bacteria
    • Eventhough a single bacteria is not complex it is far from simple in its modes of transportation, structure, diversity, and behavior.
    • Some bacteria have the ability to move away substances such as toxins, or harsh heat or light. Some species have magnetic particles that help them locate the center of the earth and swim to oxygen depletes waters deep in the ocean.
    • Some bacteria show collective behavior such as entire colonies secreting enzymes to digest particles that get stuck to the colony and the colony itself can even move an detect food.
    • Some colonies have cells that differentiate and help the entire colony produce spores that are released and go on to establish another colony.
V. Archaebacteria
  • This kingdom is divided into three major groups. The methanogens, halophiles, and extreme thermophiles.
  • These bacteria differ as much from eubacteria and they do from eukaryotic cells due to their unique composition , structure, metabolism and nucleic acid sequences.
  • Many scientists believe that the archaebacteria can withstand such extreme conditions that may have existed on early Earth that they resemble the first living cells.
    • Methanogens or methane makers live in swamps, sewage, stockyards, animal guts, and other oxygen free environments (obligate anaerobes - they die in the presence of oxygen) and humans are more closely related to them than to eubacteria. They metabolize and produce ATP very similar to our anaerobic pathways but instead of lactic acid they produce methane gas. They produce about 2 billion tons of methane every year and help to change the levels of carbon in the environment.
    • Halophiles or salt lovers live in brackish ponds, salt lakes, near volcanic fissures on the seafloor and other high-salinity settings. These bacteria can spoil salted fish, animal hides and comercially produced sea salt.
    • Extreme Thermophiles live in such places as highly acidic soils, hot springs, even coal mine wastes and hydrothermal vents. Scientists use their existence at vents as evidence that life could have originated deep in the ocean.