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Transcript
The old way: When scientists first started to classify life, everything was designated as either an animal or a plant (Aristotle). But as new forms of life were discovered and our knowledge of life on Earth grew, new categories, called "Kingdoms," were added (Linnaeus). There eventually came to be five Kingdoms in all - Animalia, Plantae, Fungi, Protista, and Bacteria. These were all categorized as either Eukarya, or Prokarya. The new way: New insight into molecular biology changed this view of life. A type of prokaryotic organism that had long been categorized as bacteria turned out to have DNA that is very different from bacterial DNA. This difference led microbiologist Carl Woese of the University of Illinois to propose reorganizing biological taxonomy into three separate Domains: Eukarya, Eubacteria (true bacteria), and Archaea. Depending upon the resource, you still may see these referred to in the “old” way. Sometimes, the eubacteria and archaebacteria are classified together in the “old” kingdom, Monera. Today, as already stated, science recognizes three Domains. Within those three, bacteria comprise two! All other life forms (kingdoms Protista, Fungi, Plantae, and Animalia) are from the Domain Eukarya. The single unifying characteristic of all organisms within this bacterial “group” is that they are all prokaryotes. • They lack true nucleus, and other membrane-bound organelles • They contain a single, “naked” chromosome consisting of a DNA molecule •Some contain “plasmids” (small, circular DNA molecules, in addition to the major chromosome) •Most have a cell wall containing peptidoglycans (a polysaccharide modified with polypeptides) (Most other organisms containing this structure, have cellulose/chitin-based cell walls.) The cell wall distinguishes two broad groups of bacteria. Gram-Positive Contain a thick peptidoglycan cell wall, which stains darkly when subjected to gram-stain A: E.coli (gram negative) B. Staphylococcus epidermidis (gram positive) c. Bacillus cereus (gram positive) Gram-Negative Contain a thin peptidoglycan wall covered with a layer of lipopolysaccharides, which doesn’t absorb the gram-stain Capsule: a sticky gelatinous coating surrounding the cell wall. A bacterium with a capsule more than likely causes disease. Flagellum: Some have long whiplike protrusions that enable them to move Nucleoid: Central region where the bacterial cell’s DNA is generally located…not a true nucleus Pilus: Extensions of the plasma membrane, help bacterium to stick to a surface, and sometimes used in the exchange of genetic material during sexual reproduction Cell Wall: surrounding the plasma membrane, it gives the cell its shape. The cell wall also prevents the osmosis of water into the cell, as bacteria typically live in a hypotonic environment. Contains less dissolved particles than inside the bacteria…so which way would water flow? Many bacteria have the ability to move. •Flagella: Consists of globular protein flagellin, arranged in helical chains (not tubulin found in eukaryotes with flagella) that rotate like screws Some species of bacteria (such as Spirochetes) have a specialized type of flagellum called an "axial filament" that is located in the periplasmic space, the rotation of which causes the entire bacterium to move forward in a corkscrew-like motion. Still others glide through slimy material that they secrete…called slime-gliding appropriately enough! • Flagella: the most common mechanism for movement. Flagella can be spread over the entire cell or concentrated at one or both ends. What globular protein makes up bacterial flagella? • Spiral Motion: In helix shaped bacteria. Moves similar to a cork screw. • Slime gliding: Cells secrete slimy threads that anchor to the host. As the cell continues to secrete a slime layers build up and the bacteria is able to glide around. • Some bacterial have no movement Autotrophs: manufacture their own organic compounds. • photoautotrophs: use sun’s energy • chemoautotrophs: use energy obtained from chemical substances (chemosynthesis) Hydrogen sulfide (H2S), ammonia (NH3), nitrite (NO2), and nitrate (NO3) • Heterotrophs: obtain their energy by consuming organic substances produced by autotrophs. • parasites: obtain energy from living host • saprobes: (saprophytes) obtain energy from dead and decaying matter. (decomposers) Obligate aerobes: Bacteria which require an oxygen environment to live Mycobacterium tuberculosis Obligate anaerobes: Bacteria which are killed in an oxygen environment. Clostridium tetani Facultative anaerobes: Grow in the presence of oxygen, but when oxygen is absent, can switch to anaerobic metabolism Staphylococcus aureus Archaebacteria Extremists: habitats where little else can live. • oxygen-free environments, producing methane Methanogens Anaerobic, living in mud and swamps, the guts of cows, humans, termites, and others • concentrated salt water Halobacterium salinarium Halophiles can cause spoilage in salted foods, and while most are heterotrophic, some are autotrophic and contain the pigment bacteriorhodopsin • hot acidic waters of sulfur springs and hydrothermal vents Thermophiles, and thermoacidophiles Eubacteria • True bacteria •Heterotrophs/parasites •Saprobes or saprotrophs •Autotrophs • cyanobacteria • chemosynthetic bacteria (Nitrifying bacteria, which turn nitrite into nitrate) •nitrogen-fixing bacteria (living mutualistically with plants) •spirochetes (use their internal flagella to move in a spiral, or corkscrew motion) Cocci: spherical shaped Bacilli: rod shaped Spirillum: spiral shaped Diplo: Arrangements of two Diplococcus Strepto: Arrangements of long chains Streptococcus Stroptobacillus Staphylo: Arrangements of grape-like clusters Staphylococcus Bacterial Shapes and Arrangements Bacteria have evolved the ability to reproduce in many different ways. • Binary Fission: A means of asexually reproducing whereby each of the two daughter cells are genetically identical to the parent Would you rather have $10 every 20 minutes for 13 hours, or one penny, doubled every 20 minutes for 13 hours? The first choice will get you $400 The second choice will get you $5 million! The growth rate for bacteria as they undergo asexual reproduction is like the second example. This kind of growth pattern is known as exponential Binary Fission in bacteria In addition to binary fission, bacteria can sexually recombine their genetic material, in a process known as conjugation. Conjugation: is NOT sexual reproduction, as one bacterium transfers all or part of its genetic material to another bacteria through the pilus. Usually, a bacterial plasmid (circular DNA) is conferred to the recipient, which benefits that bacteria. Often the plasmid contains the code for antibiotic resistance. Then, the bacteria receiving the new genetic code can reproduce by binary fission. Some bacteria, when faced with unfavorable environments produce endospores. Endospores are tiny structures that contain a bacterium’s DNA and a small amount of its cytoplasm, enclosed by a tough outer covering that is resistant to drying out, extreme temperatures, and chemical conditions. Bacillus anthracis • Nitrogen Fixation Bacteria have the ability to convert N2 into ammonia (NH3) in this process. Then other bacteria convert the ammonia into nitrite (NO2) and nitrate (NO3). Plants can use these forms of nitrogen. Humans and other heterotrophs eat the plants and receive the nitrogen in that way. Nitrogen is important because it is a component in protein, DNA, and RNA. If it weren’t for these nitrogen-fixing bacteria, all the nitrogen in the atmosphere would be unusable to life on Earth. • Recycling of nutrients Without the action of decomposing bacteria, organic materials would never break down. We would be buried in waste. As a decomposer, bacteria play a vital role in the food chain. Autotrophic bacteria also help to replenish the oxygen in Earth’s atmosphere. • Food and medicines • Streptomycin • Erythromycin Cheeses, pickles, and yogurt all rely on the action of bacteria for a variety of distinctive flavors and aromas Many types of bacteria also produce antibiotics that destroy other types of bacteria. • Neomycin Completely by accident, in 1928 Sir Alexander Fleming discovered that the airborne mold, Penicillium notatum inhibited the growth of the bacterium he was culturing. He never knew how it worked. Years later, it was discovered that the penicillin interfered with the ability of some bacteria to make cell walls. • During reproduction, cell walls developed holes • Osmosis occurred, and cells burst, killing the bacterium Don't be alarmed about the bacteria in yogurt. Everyone has bacteria inside their bodies; especially in the stomach and intestines where food is broken up and digested. When you eat yogurt, it encourages the good types of bacteria to multiply in your digestive track. These "friendly" bacteria also protect your body systems against harmful microorganisms which cause digestive upset and other infections. To put the size of the big bacterium in perspective, it is a true giant in the world of the very small. It is a huge (for the bacterial world) ¾ mm in size. Scientists, drawing an analogy, said if the largest of the newly discovered bacteria was the size of a blue whale, the typical bacterium would be the size of a new-born mouse. Into what category would you place this newly discovered bacterium? Streptococcus Thiomargarista namibiensis