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CHAPTER 28 LECTURE SLIDES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The First Cells • Microfossils are fossilized forms of microscopic life – Oldest are 3.5 billion years old – Seem to resemble present-day prokaryotes 2 • Stromatolites are mats of cyanobacterial cells that trap mineral deposits – Oldest are 2.7 billion years old – Modern forms are also known 3 • Biomarkers – Organic molecules of biological origin – Proven difficult to find – Hydrocarbons derived from fatty acid tails of lipids were found in ancient rocks • Indicates that cyanobacteria are at least 2.7 billion years old – Possible origin of life pushed back beyond 3.5 BYA 4 Prokaryotic Diversity • Oldest, structurally simplest, and most abundant forms of life • Abundant for over a billion years before eukaryotes • Less than 10% of species are known • Fall into 2 domains – Bacteria (also called Eubacteria) – Archaea (formerly called Archaebacteria) • Many archaeans are extremophiles 5 • Unicellularity – Most are single-celled – Amy stick together to form associations – Some can form complex biofilms • Cell size – Size varies tremendously – Most are less than 1 mm in diameter • Chromosome – Single circular double-stranded DNA – Found in the nucleoid region of cell – Often have plasmids • Cell division – Most divide by binary fission 6 • Genetic recombination – Occurs through horizontal gene transfer – NOT a form of reproduction • Internal compartmentalization – No membrane-bounded organelles – No internal compartment – Ribosomes differ from eukaryotic form • Flagella – Simple in structure – Different from eukaryotic flagella • Metabolic diversity – Oxygenic and anoxygenic photosynthesis – Chemolithotrophic 7 Bacteria vs. Archaea • Plasma membrane – All prokaryotes have a plasma membrane – Bacterial lipids are unbranched – Archaean membranes are formed on glycerol skeleton • Hydrocarbons may be branched or have rings 8 • Cell wall – All prokaryotes have cell walls – Bacteria have peptidoglycan – Archaea lack peptidoglycan • DNA replication – Both have single replication origin – Archaeal DNA replication is more similar to that of eukaryotes • Gene Expression – Archaeal transcription and translation are more similar to those of eukaryotes 9 Early Classification Characteristics • Relied on staining characteristics and observable phenotypes 1. Photosynthetic or nonphotosynthetic 2. Motile or nonmotile 3. Unicellular, colony-forming, or filamentous 4. Formation of spores or division by transverse binary fission 5. Importance as human pathogens or not 10 Molecular Classification 1. Amino acid sequences of key proteins 2. Percent guanine–cytosine content 3. Nucleic acid hybridization – Closely related species will have more base pairing 4. Gene and RNA sequencing – Especially rRNA 5. Whole-genome sequencing 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Domain Bacteria Domain Archaea Domain Eukarya Common ancestor 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Euryarchaeota Aquificae Bacilli Actinobacteria Spirochaetes 1 µm 1.37 µm Archaea differ greatly from bacteria. Although both are prokaryotes, archaeal cell walls lack peptidoglycan; plasma membranes are made of different kinds of lipids than bacterial plasma membranes; RNA and ribosomal proteins are more like eukaryotes than bacteria. Mostly anaerobic. Examples include Methanococcus, Thermoproteus, Halobacterium. The Aquificae represent the deepest or oldest branch of bacteria. Aquifex pyrophilus is a rodshaped hyperthermophile with a temperature optimum at 85°C; a chemoautotroph, it oxidizes hydrogen or sulfur. Several other related phyla are also thermophiles. 23.80 µm Gram-positive bacteria. Largely solitary; many form endospores. Responsible for many significant human diseases, including anthrax (Bacillus anthracis); botulism (Clostridium botulinum); and other common diseases (staphylococcus, streptococcus). 22.15 µm Some gram-positive bacteria form branching filaments and some produce spores; often mistaken for fungi. Produce many commonly used antibiotics, including streptomycin and tetracycline. One of the most common types of soil bacteria; also common in dental plaque. Streptomyces, Actinomyces. Thermophiles Crenarchaeota Euryarchaeota Aquificae Thermotogae Chloroflexi Gram-positive bacteria DeinococcusThermus Low G/C (Firmicutes) Bacilli Archaea 25.96 µm Long, coil-shaped cells that stain gramnegative. Common in aquatic environments. Rotation of internal filaments produces a corkscrew movement. Some spirochetes such as Treponema pallidum (syphilis) and Borrelia burgdorferi (Lyme disease) are significant human pathogens. Clostridium High G/C Actinobacteria Bacteria 13 a: © SPL/Photo Researchers, Inc.; b; © Dr. R. Rachel and Prof. Dr. K. O. Stetten, University of Regensburg, Lehrstuhl fuer Mikrobiologie, Regensburg, Germany; c: © Andrew Syred/SPL/Photo Researchers, Inc.; d: © Microfi ield Scientifi c Ltd/SPL/Photo Researchers, Inc.; e: © Alfred Paseika/SPL/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cyanobacteria Beta Gamma Delta 25.04 µm 10.57 µm Cyanobacteria are a form of photosynthetic bacterium common in both marine and freshwater environments. Deeply pigmented; often responsible for “blooms” in polluted waters. Both colonial and solitary forms are common. Some filamentous forms have cells specialized for nitrogen fixation. A nutritionally diverse group that includes soil bacteria like the lithotroph Nitrosomonas that recycle nitrogen within ecosystems by oxidizing the ammonium ion (NH4+). Other members are heterotrophs and photoheterotrophs. Gammas are a diverse group including photosynthetic sulfur bacteria, pathogens, like Legionella, and the enteric bacteria that inhabit animal intestines. Enterics include Escherichia coli, Salmonella (food poisoning), and Vibrio cholerae (cholera). Pseudomonas are a common form of soil bacteria, responsible for many plant diseases, and are important opportunistic pathogens. Photosynthetic Spirochaetes Cyanobacteria Chlorobi 750 µm The cells of myxobacteria exhibit gliding motility by secreting slimy polysaccharides over which masses of cells glide; when the soil dries out, cells aggregate to form upright multicellular colonies called fruiting bodies. Other delta bacteria are solitary predators that attack other bacteria (Bdellovibrio) and bacteria used in bioremediation (Geobacter). Proteobacteria Beta Gamma Alpha– Rickettsia Epsilon– Helicobacter Delta 14 f: © Dr. Robert Calentine/Visuals Unlimited; g: © Science VU/S. Watson/Visuals Unlimited; h: © Dennis Kunkel Microscopy, Inc.; i: © Prof. Dr. Hans Reichenbach, Helmholtz Centre for Infection Research, Braunschweig Prokaryotic Cell Structure • 3 basic shapes – Bacillus – Rod-shaped – Coccus – Spherical – Spirillum – Helical-shaped 15 • Cell wall – Peptidoglycan forms a rigid network • Maintains shape • Withstands hypotonic environments • Archaea have a similar molecule – Gram stain • Gram-positive bacteria have a thicker peptidoglycan wall and stain a purple color • Gram-negative bacteria contain less peptidoglycan and do not retain the purple-colored dye – retain counterstain and look pink 16 17 • Capsule – Gelatinous layer found in some bacteria – Aids in attachment – Protects from the immune system • Flagella – Slender, rigid, helical structures – Composed of the protein flagellin – Involved in locomotion – spins like propeller • Pili – Short, hairlike structures – Found in gram-negative bacteria – Aid in attachment and conjugation 18 • Endospores – Develop a thick wall around their genome and a small portion of the cytoplasm – Highly resistant to environmental stress • Especially heat – When conditions improve can germinate and return to normal cell division – Bacteria causing tetanus, botulism, and anthrax 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 0.47µm b. 0.86µm a: © Science VU/S. W. Watson/Visuals Unlimited; b: © Norma J. Lang/Biological Photo Service • Internal membrane – Invaginated regions of plasma membrane – Function in respiration or photosynthesis 20 • Nucleoid region – Contains the single, circular chromosome – May also contain plasmids • Ribosomes – Smaller than those of eukaryotes – Differ in protein and RNA content – Targeted by some antibiotics 21 Conjugation • Plasmids may encode advantageous info – Are not required for normal function • In E. coli, conjugation is based on the presence of the F plasmid (fertility factor) – F+ cells contain the plasmid – F- cells do not 22 cell produces F pilus that connects it to F cell • • Transfer of F plasmid occurs through conjugation bridge • F plasmid copied through rolling circle replication • The end result is two F+ cells F+ 23 Transformation • Natural transformation – Occurs in many bacterial species, including Streptococcus which was studied by Griffith – DNA that is released from a dead cell is picked up by another live cell – Encoded by bacterial chromosome • Not an accident of plasmid or phage biology 24 • R (resistance) plasmids – Encode antibiotic resistance genes – Acquire genes through transposable elements – Important factor in appearance of antibiotic resistant strains of Staphylococcus aureus • Virulence plasmids or transduction – Encode genes for pathogenic traits – Enterobacteriaceae – E. coli O157:H7 strain 25 • Mutations can arise spontaneously in bacteria as with any organism – Radiation and chemicals increase likelihood • Mutations (and plasmids) can spread rapidly in a population – Methicilin-resistant Staphylococcus aureus (MRSA) – Vancomycin-resistant Staphylococcus aureus (VRSA) 26 Human Bacterial Disease • In the early 20th century, infectious diseases killed 20% of children before the age of five – Sanitation and antibiotics considerably improved the situation • In recent years, however, many bacterial diseases have appeared and reappeared 27 Tuberculosis (TB) • • • • • Scourge for thousands of years Mycobacterium tuberculosis Afflicts the respiratory system Thwarts immune system Easily transferred from person to person through the air • Multidrug-resistant (MDR) strains are very alarming 28 • Dental caries (tooth decay) – Plaque consists of bacterial biofilms – Streptococcus sobrinus ferments sugar to lactic acid – Tooth enamel degenerates • Peptic ulcers – Helicobacter pylori is the main cause – Treated with antibiotics 29 Sexually transmitted diseases (STDs) • Gonorrhea – One of the most prevalent communicable diseases in North America. – Neisseria gonorrhoeae – Transmitted through exchange of body fluids – Can pass from mom to baby via birth canal • Chlamydia – Chlamydia trachomatis – “Silent STD” – incidence has skyrocketed – Can cause PID and heart disease 30 • Syphilis – Treponema pallidum – Transmitted through sex or contact with open chancre – Can pass from mom to baby via birth canal – Four distinct stages • Primary – Chancre – highly infectious • Secondary – Rash – infectious • Tertiary – Latency – no longer infectious but attacking internal organs • Quaternary – Damage now evident 31 32 Beneficial Prokaryotes • Decomposers release a dead organism’s atoms to the environment • Fixation – Photosynthesizers fix carbon into sugars • Ancient cyanobacteria added oxygen to air – Nitrogen fixers reduce N2 to NH3 (ammonia) • Anabaena in aquatic environments • Rhizobium in soil 33 • Symbiosis refers to the ecological relationship between different species that live in direct contact with each other – Mutualism – both parties benefit • Nitrogen-fixing bacteria on plant roots • Cellulase-producing bacteria in animals – Commensalism – one organism benefits and the other is unaffected – Parasitism – one organism benefits and the other is harmed 34 • Bacteria are used in genetic engineering – “Biofactories” that produce various chemicals, including insulin and antibiotics • Bacteria are used for bioremediation – Remove pollutants from water, air, and soil – Biostimulation – adds nutrients to encourage growth of naturally occurring microbes • Exxon Valdez oil spill 35