BIOL 102 Chp 27 PowerPoint Spr10
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BIOL 102 Chp 27 PowerPoint Spr10 BIOL 102 Chp 27 PowerPoint Spr10 Presentation Transcript

  • Chp 27 Bacteria & Archaea Rob Swatski Assistant Professor of Biology HACC – York Campus
  • Overview: Masters of Adaptation • Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • They have an astonishing genetic diversity • There are more in a handful of fertile soil than the number of people who have ever lived!!!
  • Structural & functional adaptations contribute to prokaryotic success • Prokaryotes are divided into two domains: Bacteria & Archaea • Most prokaryotes are unicellular, although some species form colonies • Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Bacteria on Cheek Epithelial Cells - 5500X
  • • Prokaryotic cells have a variety of shapes - the 3 most common shapes are spheres (cocci), rods (bacilli), & spirals
  • 1 µm 2 µm 5 µm (a) Spherical (b) Rod-shaped (c) Spiral (cocci) (bacilli)
  • Cell-Surface Structures • An important feature of nearly all prokaryotic cells is their cell wall - maintains cell shape - provides physical protection - prevents the cell from bursting in a hypotonic environment • Eukaryote cell walls are made of cellulose or chitin • Bacterial cell walls contain peptidoglycan - network of sugar polymers cross-linked by polypeptides Peptidoglycan animation
  • • Archaea contain polysaccharides & proteins but lack peptidoglycan • Using the Gram stain, scientists classify many bacterial species into Gram-positive & Gram- negative groups based on cell wall composition • Gram-negative bacteria: - have less peptidoglycan - outer membrane can be toxic - more likely to be antibiotic resistant (many antibiotics target peptidoglycan & damage cell walls)
  • Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.
  • Peptidoglycan Cell layer wall Plasma membrane Protein (a) Gram-positive: peptidoglycan traps crystal violet. (P = “+” purple)
  • Gram- Gram- positive negative bacteria bacteria 20 µm
  • Fimbriae Cell wall Circular chromosome Capsule Sex pilus Internal organization Flagellae
  • Capsule: polysaccharide or protein layer covers many prokaryotes Capsule
  • Some prokaryotes also have fimbriae (attachment pili) - allows them to stick to substrates or to other individuals in colony Fimbriae, UTI's, & Cranberry Juice Sex pili are longer than fimbriae - allow prokaryotes to exchange DNA Fimbriae
  • Motility • Most motile bacteria propel themselves by flagella - structurally & functionally different from eukaryotic flagella • Many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Chemotaxis!
  • Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane
  • Internal & Genomic Organization Prokaryotic cells usually lack complex compartmentalization But, some do have specialized membranes that perform metabolic functions
  • 0.2 µm 1 µm Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote
  • • The prokaryotic genome has less DNA than the eukaryotic genome • Most of the genome consists of a circular chromosome - the DNA is not surrounded by a membrane & is located in a nucleoid region • Some species of bacteria also have smaller rings of DNA called plasmids
  • Chromosome Plasmids 1 µm
  • Reproduction & Adaptation • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours • Many form metabolically inactive endospores - can remain viable in harsh conditions for centuries
  • Endospore formation in Lyme bacteria Endospore 0.3 µm
  • Prokaryotes can EXPERIMENT evolve rapidly Daily serial transfer 0.1 mL because of their (population sample) short generation times Old tube New tube (discarded (9.9 mL after growth transfer) medium) RESULTS 1.8 1.6 Fitness relative to ancestor 1.4 1.2 1.0 0 5,000 10,000 15,000 20,000 Generation
  • Prokaryotes have considerable genetic variation 3 factors contribute to this genetic diversity: - Rapid reproduction - Mutation - Genetic recombination
  • Rapid Reproduction & Mutation • Prokaryotes reproduce by binary fission - offspring cells are generally identical • Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population • High diversity from mutations allows for rapid evolution Binary Fission in Bacteria
  • Genetic Recombination Prokaryotic DNA from different individuals can be brought together by: - transformation - transduction - conjugation
  • Transformation: a cell takes up & incorporates foreign DNA from the surrounding environment Transformation in Bacteria animation Transduction: the movement of genes between bacteria by bacteriophages (viruses that infect bacteria) Bacteriophage animation
  • Transduction Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell
  • Conjugation: - DNA is transferred between bacterial cells - Sex pili allow cells to connect & pull together for DNA transfer • A piece of DNA called the “F” factor is required for the production of sex pili - the F factor can exist as a separate plasmid or as DNA within the bacterial chromosome
  • Sex pilus 1 µm
  • The “F” Factor as a Plasmid “F” factor is transferable during conjugation as an F plasmid • Cells with the F plasmid function as DNA donors during conjugation • Cells without the F plasmid function as DNA recipients during conjugation
  • Conjugation & recombination of an F plasmid in E. coli F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge Bacterial chromosome F+ cell F– cell The F- cell is the DNA recipient
  • The “F” Factor in the Chromosome • A cell with the F factor built into its chromosomes functions as a DNA donor during conjugation • The recipient becomes a recombinant bacterium, with DNA from 2 different cells
  • Conjugation & transfer of part of an Hfr bacterial chromosome in E. coli Hfr cell Recombinant A+ A+ F– bacterium A+ A+ A– A+ F factor A– A– A+ A– F– cell
  • 4 Major Modes of Nutrition • Photoautotrophy: obtain energy from light • Chemoautotrophy: obtain energy from chemicals • Photoheterotrophy: require CO2 as a carbon source • Chemoheterotrophy: require an organic nutrient to make organic compounds
  • The Role of Oxygen in Metabolism • Obligate aerobes: require O2 for cellular respiration • Obligate anaerobes: are poisoned by O2 & use fermentation or anaerobic respiration • Facultative anaerobes: can survive with or without O2
  • Nitrogen Metabolism • Prokaryotes can metabolize nitrogen in a variety of ways • Nitrogen fixation: convert atmospheric nitrogen (N2) to ammonia (NH3)
  • Metabolic Cooperation • Metabolic cooperation: allows prokaryotes to use environmental resources they could not use as individual cells • In the cyanobacterium Anabaena, photosynthetic cells & heterocytes (nitrogen-fixing cells) exchange metabolic products Cyanobacteria!
  • Photosynthetic cells Heterocyte 20 µm
  • Metabolic cooperation can occur in surface-coating colonies called biofilms Your Own Personal Biofilm! Tooth Biofilm video
  • Look Closer!!!
  • Molecular systematics is illuminating prokaryotic phylogeny Before the late 20th century, systematists based prokaryotic taxonomy on phenotypic criteria Applying molecular systematics to prokaryotic phylogeny has produced dramatic results - has led to a phylogenetic classification of prokaryotes - major new clades have been identified
  • Eukarya Domain Eukaryotes Korarcheotes Domain Archaea Euryarchaeotes Crenarchaeotes UNIVERSAL Nanoarchaeotes ANCESTOR Proteobacteria Domain Bacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria
  • The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes - A handful of soil many contain 10,000 prokaryotic species!!! Horizontal gene transfer between prokaryotes obscures the root of the tree of life
  • PCR Animation
  • Archaea Archaea share certain traits with Bacteria & other traits with Eukarya Eukarya Archaea Bacteria
  • Extremophile Archaea Extremophiles: live in harsh environments • Extreme halophiles: live in very saline environments • Extreme thermophiles: thrive in very hot environments Acid-Loving Archaea
  • <Sniff> <Sniff> ... Do you smell something?
  • • Methanogens live in swamps & marshes - produce methane as a waste product - strict anaerobes & are poisoned by O2 In recent years, genetic prospecting has revealed many new groups of Archaea - some may offer clues to the early evolution of life
  • 54
  • 2.5 µm Rhizobium (arrows) inside a root cell of a legume (TEM)
  • Soil bacterium Nitrosomonas - converts NH4+ to NO2–
  • Slime-secreting myxobacteria Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM)
  • B. bacteriophorus 5 µm Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM)
  • Pathogens - Campylobacter (blood poisoning) - Helicobacter pylori (stomach ulcers) Helicobacter pylori
  • Spirochetes Helical heterotrophs - Treponema pallidum (syphilis) - Borrelia burgdorferi (Lyme disease)
  • Cyanobacteria Photoautotrophs that generate O2 Plant chloroplasts likely evolved from cyanobacteria - endosymbiosis
  • 1 µm Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)
  • Chemical Cycling Chemoheterotrophic prokaryotes: decomposers - break down corpses, dead vegetation, & wastes Nitrogen-fixing bacteria: - add usable N to the environment
  • Ecological Interactions Symbiosis: - larger host - smaller symbiont
  • Mutualism: Commensalism: Parasitism:
  • Pathogenic Prokaryotes
  • Pathogenic prokaryotes typically cause disease by: Exotoxins: - cause disease even if the prokaryotes that produce them are not present Endotoxins: - released only when bacteria die & cell walls break down
  • Prokaryotes in Research & Technology Biotechnology Bioremediation
  • Bioremediation
  • Other Uses of Prokaryotes: - Mining - Vitamin synthesis - Antibiotics & hormone synthesis