1 - microbial world and prokaryotic cell anatomy
TRANSCRIPT
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Lecture 1: Microbial World and Procaryotic Cell Anatomy
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Microbes/Microorganisms?
• Too small to see with the “naked” eye• Beneficial
– Ecological: Recycle nutrients• Bioremediation
– Industrial: Food, chemicals, drugs• Fermented Foods• Antibiotics• Ethanol and other chemicals• Enzymes – Cellulase, Peroxidase
• Destructive/Pathogenic– FEW
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Nomenclature
• Scientific Nomenclature– System devised by Linnaeus
• Genus and species– Both italicized or underlined– Genus name Upper-case; species lower-case
– Name describes the organism• Ex. Staphylococcus aureus
– Staphylococcus: cluster of spheres– aureus: golden aura of colonies
– Name honors the scientist• Ex. Escherichia coli
– Escherich: honors the discoverer, Theodor Escherich– coli- describes the habitat – the colon or the small intestine
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Three Domains of Life– Archaea
• prokaryotes• Primarily extremophiles• Not disease-causing
– Bacteria• prokaryotes
– Eukarya• Nucleated organisms• Uni- or multi-cellular• Fungi• Protista• Plants• Animals
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Classification of Microbes
• Archaea• Bacteria• Fungi• Algae• Protozoa• Multicellular Animal Parasites• Viruses
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Classification of Microbes
BacteriaSporangia
Prey
Pseudopods
CD4+ T cell HIVs
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Archaea
• Prokaryotes• No peptidoglycan in cell wall• Habitat
– Extreme environments• Methanogens (methane)• Halophiles (salt)• Thermophiles (heat)
• Not known to cause disease in humans
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Bacteria
• Prokaryotes• Cell structure
– Bacillus, Coccus, Spiral• Cell wall
– Peptidoglycan• Cell Division
– Binary Fission• Metabolism: Energy source
– Inorganic/ organic chemicals– Photosynthesis
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Fungi
• Eukaryotes• Chitin cell walls• Energy Source:
– Organic matter • Multicellular
– Molds and mushrooms • Unicellular
– Yeasts
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Protozoa• Eukaryotes• Unicellular• Motile
– Pseudopodia– Cilia– Flagella
• Shape– Variety of shapes
• Habitat– free entities or parasites
• Energy source– organic compounds
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Algae
• Eukaryotes• Cellulose cell walls• Energy source
– Photosynthesis• Produce molecular oxygen and organic
compounds
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Viruses
• Neither eukaryote or prokaryote• Acellular• Obligate Intracellular Parasites
– Only replicate when present in living host cell• Genetic Material
– Either DNA or RNA• Structure
– Nucleocapsid• Nucleic acid core• Protein coat surrounds core
– Lipid Envelope• Not always present
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Multicellular Animal Parasites
• Eukaryotes• Multicellular• Parasitic flatworms and roundworms.
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Conditions Results
Nutrient broth placed in flask, heated, NOT sealed
Microbial growth
Nutrient broth placed in flask, heated, then sealed
No microbial growth
Louis Pasteur• 1861: Louis Pasteur demonstrated that
microorganisms are present in the air
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Important Events in Microbiology
• Germ Theory of Disease– Germs present in the air cause disease, spoil food
• Louis Pasteur’s work
– Cleaning with disinfectants decreases infection• Joseph Lister’s work
• Vaccination– Jenner – Pasteur (small pox)
• Discovery of Antibiotics and Synthetic Drugs– Fleming – Penicillin– Sulfa drugs
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The Birth of Modern Chemotherapy
• Chemotherapy– Treatment with chemicals
• Treatment of infections– Antibiotics
• Naturally synthesized• bacteria and fungi
– Synthetic Drugs• Artificially synthesized• First Drugs: Sulfa drugs
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A Fortunate Accident—Antibiotics
• 1928: Alexander Fleming discovered the first antibiotic
• Fleming observed that Penicillium fungus made an antibiotic, penicillin, that killed S. aureus
• 1940s: Penicillin was tested clinically and mass produced
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Normalbacterialcolony
Area of inhibition of bacterial growth
Penicilliumcolony
Figure 1.5 The discovery of penicillin.
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Microbes in Human Welfare
• Microbial ecology: – Bacteria recycle inorganic material
• carbon, sulfur, phosphorus • Used by plants and animals
– Turns N to Nitrates and Nitrites so plants can use it
• Bioremediation: – Bacteria degrade organic matter
• Sewage treatment• Detoxify pollutants
– Oil and mercury spills
• Biotechnology
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Biotechnology
• Recombinant DNA technology – Taking parts of DNA and recombining it back into the DNA (E. coli produces purple because
it was engineered then recombined into the DNA to make it happen)
– Engineer viruses, bacteria and fungi• Produce proteins
– Vaccines, enzymes, hormones
– Gene therapy• Replace missing or defective genes in human cells
– Hemophilia– Blindness
– Agriculture• Genetically modified bacteria
– Protect crops from insects and freezing
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Normal Microbiota/ Normal Flora
• Nomenclature– Old: Normal Flora
• Because bacteria initially classified as plants
– New: Normal microbiota• Microbes present on or in the human body
– prevent growth of pathogens– produce growth factors, such as folic acid and
vitamin K
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Biofilms Complex aggregation of microbes Microbes attach to solid surfaces and grow into
masses grow on rocks, pipes, teeth, and medical implants Difficult to treat with antibiotics
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Infectious Diseases
When a pathogen overcomes the host’s resistance, disease results
Emerging infectious diseases (EIDs): New diseases and diseases increasing in incidence
1. Evolutionary2. Increased human exposure in undergoing
ecological changes3. Antimicrobial resistance
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MRSA
• Methicillin-resistant Staphylococcus aureus• 1950s: Penicillin resistance developed• 1980s: Methicillin resistance• 1990s: MRSA resistance to vancomycin
reported– VISA: Vancomycin-intermediate-resistant S. aureus – VRSA: Vancomycin-resistant S. aureus
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Figure 25.12
Escherichia coli O157:H7• Toxin-producing
strain of E. coli• First seen in 1982• Leading cause of
diarrhea worldwide
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Figure 23.21
Ebola Hemorrhagic Fever
• Ebola virus• Causes fever, hemorrhaging, and blood
clotting• First identified near Ebola River, Congo• Outbreaks every few years
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Prokaryotic Anatomy
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Average size: 0.2–1.0 µm in diameter 2–8 µm in length (10^-6 meters)
Most bacteria are monomorphic (single shape)
What can alter shape? Cell wall (membrane or wall)
Prokaryotic Cells: Shapes
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Figure 4.2b-c Bacilli.
Streptobacilli
Diplobacilli
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Figure 4.1ad Arrangements of cocci.
Plane of division
Diplococci
Streptococci
Staphylococci
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Arrangements
• Pairs: diplococci, diplobacilli
• Clusters: staphylococci or staphylobacilli• More than one plane of division
• Chains: streptococci, streptobacilli• One plane of division• Grows in strands
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Vibrio
Spirochete
Spirillum
Figure 4.4 Spiral bacteria.
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Star-shaped bacteria
Figure 4.5a Star-shaped and rectangular prokaryotes.
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Rectangular bacteria
Figure 4.5b Star-shaped and rectangular prokaryotes.
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Figure 4.6 The Structure of a Prokaryotic Cell.
Capsule
Cell wall
Plasmamembrane
Fimbriae
Cytoplasm
Pilus
70S Ribosomes
Plasma membrane
Inclusions
Nucleoid containing DNA
Plasmid
Flagella
CapsuleCell wall
.
Not all bacteria have all the structures shown; only structures labeled in red are found in all bacteria.
Although the nucleoid appears split in the photomicrograph, the thinness of the “slice” does not convey the object’s depth.
© 2013 Pearson Education, Inc.
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Bacterial Cell: Specific Roles
• Capsule: bacterial virulence• Cell Wall or Flagella: bacterial identification• Cell Wall: target for antimicrobial agents• Plasmids: encode genes for production of
toxins– Circular DNA that is independent to all the rest of
the chromosomal DNA. They are not needed for the survival unless an it contains genetics that help it in it’s outside living conditions
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Glycocalyx
Outside cell wall Usually sticky, “sugar coating” (glue) Capsule: neatly organized Slime layer: unorganized and loose (EPS) Extracellular polysaccharide (glycocalyx in
general) allows cell to attach, chemical composition varies by species
Capsules (negative stain [will not stain]) prevent phagocytosis
Example: Streptococcus pneumoniae
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Figure 24.12 Streptococcus pneumoniae, the cause of pneumococcal pneumonia.
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Flagella• Motility
– Propel bacteria (word to move is taxis [move to light=phototaxis])
• Long filamentous appendages– Three basic parts
• Filament (outermost region): globular protein• Hook: different protein• Basal body
• Anchored to cell wall and membrane by the basal body
• Distribution– No Flagella: ATRICHOUS– Evenly distributed: PERITRICHOUS– Polar: at one or both poles/ends
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Figure 4.7 Arrangements of bacterial flagella.
Peritrichous Monotrichous and polar
Lophotrichous and polar Amphitrichous and polar
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Basal body
Peptidoglycan
Hook
Cell wall
Gram-positive
Filament
Flagellum
Plasmamembrane
Cytoplasm
Parts and attachment of a flagellum of a gram-positive bacterium
Figure 4.8b The structure of a prokaryotic flagellum.
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Plasmamembrane
Cell wallBasal body
Gram-negative
Peptidoglycan
Outermembrane
Hook
Filament
Cytoplasm
Flagellum
Parts and attachment of a flagellum of a gram-negative bacterium
Figure 4.8a The structure of a prokaryotic flagellum.
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Motility
• The ability of an organism to move by itself toward a favorable environment (taxis)
• Chemotaxis signals: oxygen, ribose and galactose receptors
• Flagella proteins are H antigens (e.g., E. coli O157:H7)
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Axial Filaments
• Also called endoflagella• In spirochetes• Anchored at one end of a cell• Rotation causes cell to move• Treponema pallidum: syphilis
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Figure 4.10a Axial filaments.
A photomicrograph of the spirochete Leptospira, showing an axial filament
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• Thinner than flagellum• Attachment and DNA transfer • Fimbriae allow attachment: involved in
forming biofilms• What happens if fimbriae are absent (genetic
mutation)?– Becomes less virilant, disallows attachment
Fimbriae and Pili
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Figure 4.11 Fimbriae.
Fimbriae
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Fimbriae and Pili
• Pili – Usually longer than fimbriae – Gliding motility– Twitching motility (like a worm)
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The Cell Wall
• Major function: prevents osmotic lysis• Maintains shape and point of anchorage for
basal bodies• Made of peptidoglycan (in bacteria)• Gram positive and Gram negative
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Peptidoglycan
• Major component of cell wall in bacteria• Polymer of sugars and amino acids
– Form a mesh-like layer – Each strand two sugars linked alternatively
• N-acetylglucosamine• N-acetylmuramic acid
– peptide chain of three to five amino acids. – peptide chain of one strand cross-linked to the peptide chain
of another strand forming the 3D mesh-like layer.
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L-Ala, d-Glu-NH2 etc. are amino acids
This is the cell wall, the more ladders,the thicker the wall is
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• Thick peptidoglycan• Teichoic acids
– makes the wall like crosshairs + where – is peptidoglycan and | is teichoic acids
Gram-PositiveCell Wall
Thin peptidoglycan Outer membrane
Gram-NegativeCell Wall
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Plasmamembrane
Cell wallLipoteichoicacid
PeptidoglycanWall teichoic acid
Protein
Gram-negative cell wall
Lipopolysaccharide
Outer membrane
PeptidoglycanPlasmamembrane
Cell wall
Lipid A Porin protein
Phospholipid
Lipoprotein
Periplasm Protein
Lipid A
Core polysaccharide
O polysaccharide
Parts of the LPS
Core polysaccharide
O polysaccharide
Gram-positive cell wall
Figure 4.13b-c Bacterial cell walls.
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• Many layers (thick) of peptidoglycan • Teichoic acids
– Alcohol and phosphate; negative charge • May regulate movement of cations: cell
growth, preventing extensive wall break down and possible cell lysis
• Polysaccharides provide antigenic variation = identification
Gram-Positive Cell Walls
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• Thin layer of peptidoglycan and an outer membrane
• Lipopolysaccharides (LPS) (outer)• LPS: evade phagocytosis and actions of
immunity, provide barrier to certain antibiotics and enzymes
• Porins: proteins that form channels, selective permeability
Gram-Negative Cell Wall
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Gram-Negative Outer Membrane
LPS Composition: Lipid A – functions as an endotoxin ,
responsible for symptoms associated with gram - infections
Core Polysaccharide – attached to Lipid A, provides stability
O Polysaccharide – functions as an antigen, useful in identification
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The Gram Stain Mechanism
• Crystal violet-iodine crystals form in cell• Gram-positive: Purple
– Alcohol dehydrates peptidoglycan– CV-I crystals do not leave
• Gram-negative: Red– Alcohol dissolves outer membrane and leaves
holes in peptidoglycan– CV-I washes out
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• 2-ring basal body– In the membrane
• Thick Peptidoglycan• Purple Gram Stain• Disrupted by
lysozyme (breaks the bonds between NAM’s and NAG’s
• Penicillin sensitive• Exotoxins
Gram-PositiveCell Wall
4-ring basal body 1 outer 1 wall 2 inner
Thin Peptidoglycan Red Gram Stain Outer Membrane Tetracycline sensitive Exo and Endotoxins
Gram-NegativeCell Wall
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Damage to the Cell Wall
• Exposure to digestive enzyme lysozyme, destroys peptidoglycan (gram positive)
• Penicillin inhibits peptide bridges in peptidoglycan (prevents formation of functioning cell wall)
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The Plasma Membrane
• Contains enzymes for metabolic reactions • Most lack sterols, Mycoplasma is exception• Disruption: membrane’s phospholipids =
antibiotics: polymyxins
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Cytoplasm
• Contains nucleoid, ribosomes and inclusions• 80% water and contains primarily proteins
(enzymes), carbs, lipids, inorganic ions and many lower molecular weight compounds
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The Nucleoid
• Bacterial chromosome: cell’s genetic information• Not surround by a nuclear envelope • Plasmids: not connected to main bacterial
chromosome but have very important functionsAntibiotic resistanceTolerance to toxic metalsProduction of toxins Can be transferred from one bacterium to another
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The Prokaryotic Ribosome
Protein synthesis Consist of two subunits: protein and type of RNA (rRNA) Prokaryotic: 70S ribosomes
50S(subunit = protein plus two molecules of rRNA) + 30S subunits (subunit = protein plus one molecule rRNA)
Antibiotics: inhibit protein synthesis. Examples: gentamicin and streptomycin attach to 30S subunit and interfere with protein synthesis
Erythromycin and chloramphenicol interfere with 50SWhy can these antibiotic drugs work without affecting host cells? Host cells are made up of 80S ribosomes
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Inclusions
• Located within cytoplasm• Reserve deposits: environment is deficient • Some are common to a wide variety of
bacteria• May serve as a basis for identification • Example: C. diphtheriae
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Endospores
• Resting cells: when essential nutrients are depleted
• Resistant to desiccation, heat, chemicals• Bacillus, Clostridium; Gram positive • Sporulation: endospore formation• Germination: return to vegetative state
– Germination <-> Sporulation