Bacterial Anatomy, Nutrition, Growth, Metabolism and Genetics

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Bacterial Anatomy, Nutrition, Growth, Metabolism
and Genetics
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Bacterial anatomy
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Generalized structure of a prokaryotic cell
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Appendages Cell Extensions? The Flagella

• 3 parts
• filament
• long, thin, helical structure composed of
  proteins
• Hook
• curved sheath
• basal body
• stack of rings firmly anchored in cell wall
• rotates 360o
• 1-2 or many distributed over entire cell
• functions in motility

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Flagellar Arrangements

• monotrichous single flagellum at one end
• lophotrichous small bunches arising from one
  end of cell
• amphitrichous flagella at both ends of cell
• peritrichous flagella dispersed over surface of
  cell, slowest

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Polar verse Peritrichous
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Chemotaxis
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Internal Flagella ? Axial Filaments

• aka Periplasmic
• Internal flagella
• enclosed between cell wall and cell membrane of
  spirochetes
• motility

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Appendages for Attachment ? Fimbrae

• fine hairlike bristles from the cell surface
• function in adhesion to other cells and surfaces

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Appendages for Mating? Pili

• rigid tubular structure
• made of pilin protein
• found only in Gram negative cells
• Functions
• joins bacterial cells for DNA transfer
  (conjugation)
• adhesion

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The Bacterial Surface Coating? Glycocalyx

• Coating of molecules external to the cell wall
• Made of sugars and/or proteins
• functions
• attachment
• inhibits killing by white blood cells
• receptor

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The Bacterial Surface Coating? Glycocalyx

• 2 types
• capsule - highly organized, tightly attached
• slime layer - loosely organized and attached

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The Structure of the Cell Wall? Peptidoglycan

• macromolecule composed of a repeating framework
  of long glycan chains cross-linked by short
  peptide fragments
• provides strong, flexible support to keep
  bacteria from bursting or collapsing because of
  changes in osmotic pressure

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The Cell Envelope

• External covering outside the cytoplasm
• Composed of two basic layers
• cell wall and cell membrane
• Maintains cell integrity
• Two generally different groups of bacteria
  demonstrated by Gram stain
• Gram-positive bacteria
• Gram-negative bacteria

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4 Groups Based on Cell Wall Composition

• Gram positive cells
• Gram negative cells
• Bacteria without cell walls
• Bacteria with chemically unique cell walls

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Gram Positive Cell Wall

• Consists of
• a thick, homogenous sheath of peptidoglycan 20-80
  nm thick
• tightly bound acidic polysaccharides
• including teichoic acid and lipoteichoic acid
• cell membrane
• Retain crystal violet and stain purple

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Gram Negative Cell Wall

• Consists of
• an outer membrane containing lipopolysaccharide
  (LPS)
• thin shell of peptidoglycan
• periplasmic space
• inner membrane
• Lose crystal violet and stain red from safranin
  counterstain
• Protective structure while providing some
  flexibility and sensitivity to lysis

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Gram Negative Cell Wall

• LPS
• endotoxin that may become toxic when released
  during infections
• may function as receptors and blocking immune
  response
• contains porin proteins in upper layer
• Regulates molecules entering and leaving cell

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The Gram Stain

• Differential stain
• Gram-negative
• lose crystal violet and stain red from safranin
  counterstain
• Gram-positive
• retain crystal violet and stain purple
• Important basis of bacterial classification and
  identification
• Practical aid in diagnosing infection and guiding
  drug treatment

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Atypical Cell Walls

• Some bacterial groups lack typical cell wall
  structure
• Mycobacterium and Nocardia
• Gram-positive cell wall structure with lipid
  mycolic acid
• pathogenicity
• high degree of resistance to certain chemicals
  and dyes
• basis for acid-fast stain
• Some have no cell wall
• Mycoplasma
• cell wall is stabilized by sterols
• pleomorphic

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Cytoplasm

• dense gelatinous solution of sugars, amino acids,
  salts
• 70-80 water
• serves as solvent for materials used in all cell
  functions

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Chromosome

• single, circular, double-stranded DNA molecule
• contains all the genetic information required by
  a cell
• DNA is tightly coiled around a protein
• dense area called the nucleoid

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Plasmids

• small circular, double-stranded DNA
• free or integrated into the chromosome
• duplicated and passed on to offspring
• not essential to bacterial growth metabolism
• may encode antibiotic resistance, tolerance to
  toxic metals, enzymes toxins
• used in genetic engineering- readily manipulated
  transferred from cell to cell

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Site of Protein Synthesis? Ribosomes

• prokaryotic differ from eukaryotic ribosomes in
  size number of proteins
• site of protein synthesis
• all cells have ribosomes

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Storage Bodies? Inclusions Granules

• intracellular storage bodies
• vary in size, number content
• Examples
• Glycogen
• poly-b-hydroxybutyrate
• gas vesicles for floating
• sulfur
• polyphosphate granules

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Endospores

• resting, dormant cells
• produced by some G genera
• Clostridium, Bacillus Sporosarcina
• have a 2-phase life cycle
• vegetative cell
• endospore
• sporulation
• formation of endospores
• Germination
• return to vegetative growth
• withstand extremes in heat, drying, freezing,
  radiation chemicals

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Endospores

• resistance linked to high levels of calcium
  certain acids
• longevity verges on immortality
• 25 to 250 million years
• pressurized steam at 120oC for 20-30 minutes will
  destroy

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Microbial nutrition, growth, and metabolism
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Microbial Nutrition

• nutrition
• process by which chemical substances (nutrients)
  are acquired from the environment and used for
  cellular activities
• essential nutrients
• must be provided to an organism
• Two categories of essential nutrients
• macronutrients
• micronutrients or trace elements

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Microbial Nutrition

• macronutrients
• required in large quantities
• role in cell structure and metabolism
• proteins, carbohydrates
• micronutrients or trace elements
• required in small amounts
• involved in enzyme function and maintenance of
  protein structure
• manganese, zinc, nickel

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Nutrients

• Inorganic nutrients
• atom or molecule that contains a combination of
  atoms other than carbon and hydrogen
• metals and their salts (magnesium sulfate, ferric
  nitrate, sodium phosphate), gases (oxygen, carbon
  dioxide) and water
• Organic nutrients
• contain carbon and hydrogen atoms and are usually
  the products of living things
• methane (CH4), carbohydrates, lipids, proteins,
  and nucleic acids

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Chemical Composition of Cytoplasm

• 70 water
• Proteins
• 96 of cell is composed of 6 elements
• Carbon
• Nitrogen
• Oxygen
• Hydrogen
• Phosphorous
• Sulfur

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Obtaining Carbon

• Heterotroph
• organism that obtains carbon in an organic form
  made by other living organisms
• proteins, carbohydrates, lipids and nucleic acids
• Autotroph
• an organism that uses CO2 (an inorganic gas) as
  its carbon source
• not dependent on other living things

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Important Mineral Ions

• Potassium
• Sodium
• Calcium

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Important Mineral Ions

• Magnesium
• Iron

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Growth Factors

• organic compounds that cannot be synthesized by
  an organism must be provided as a nutrient
• essential amino acids, vitamins
• Nutritional types
• Chemo-
• Chemical compounds
• Photo-
• light

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Other Heterotrophs

• Saprobes
• decompose dead organisms
• recycle elements
• release enzymes to digest materials
• Parasites
• utilize tissues and fluids of a living host
• cause harm

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Extracellular Digestion

• digestion of complex nutrient material into
  simple, absorbable nutrients
• accomplished through the secretion of enzymes
  (exoenzymes) into the extracellular environment

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Environmental Influences on Microbial Growth

• 1. temperature
• 2. oxygen requirements
• 3. pH
• 4. Osmotic pressure
• 5. UV light
• 6. Barophiles

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1. Temperatures

• Minimum temperature
• lowest temperature that permits a microbes
  growth and metabolism
• Maximum temperature
• highest temperature that permits a microbes
  growth and metabolism
• Optimum temperature
• promotes the fastest rate of growth and metabolism

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Temperature Adaptation Groups

• Psychrophiles
• optimum temperature below 15oC, capable of growth
  at 0oC
• Mesophiles
• optimum temperature 20o-40oC, most human
  pathogens
• Thermophiles
• optimum temperature greater than 45oC

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2. Oxygen Requirements

• Aerobe
• requires oxygen
• Obligate aerobe
• cannot grow without oxygen
• Facultative anaerobe
• capable of growth in the absence OR presence of
  oxygen
• Microaerophile
• does not grow at normal atmospheric tensions of
  oxygen
• i.e., the soil, water or the human body

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2. Oxygen Requirements

• Anaerobe
• does not require oxygen
• Capnophiles
• Higher CO2
• Aerotolerant anaerobes
• does not utilize oxygen but can survive and grow
  to limited extent in its presence

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3. pH

• The pH Scale
• Ranges from 0 - 14
• pH below 7 is acidic
• H gt OH-
• pH above 7 is alkaline
• OH- gt H
• pH of 7 is neutral
• H OH-

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3. pH

• Alkaphiles
• optimum pH is relatively to highly acidic
• Neutrophiles
• optimum pH ranges about pH 7 (plus or minus)
• Acidophiles
• optimum pH is relatively to highly basic

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4. Osmotic Pressure

• Bacteria 80 water
• Require water to grow
• Sufficiently hypertonic media at concentrations
  greater than those inside the cell (such as 20
  sucrose) cause water loss from the cell
• Osmosis
• Fluid leaves the bacteria causing the cell to
  contract
• Causes the cell membrane to separate
• Plasmolysis
• Cell shrinkage
• extreme or obligate halophiles
• Adapted to and require high salt concentrations

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5. UV Light

• Great for killing bacteria
• Damages the DNA (making little breaks)
• in sufficient quantity can kill the organisms
• in a lower range causes mutagenisis
• Spores tend to be resistant
• can survive much longer exposures

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6. Barophiles

• Bacteria that grow at moderately high hydrostatic
  pressures
• Oceans
• Barotolerants
• Grows at pressures from 100-500 Atm
• Barophilic
• 400-500
• Extreme barophilic
• Higher than 500

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Microbial Associations

• Symbiotic
• organisms live in close nutritional
  relationships
• Mutualism
• Obligatory
• Dependent
• Both members benefit
• Commensalism
• One member benefits
• Other member not harmed
• Parasitism
• Parasite is dependent and benefits
• Host is harmed

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Microbial Associations

• Non-symbiotic
• organisms are free-living
• relationships not required for survival
• Synergism
• members cooperate and share nutrients
• Antagonism
• some member are inhibited or destroyed by others

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Microbial Growth

• Binary fission
• one cell becomes two
• basis for population growth
• Process
• parent cell enlarges
• duplicates its chromosome
• forms a central septum
• divides the cell into two daughter cells

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Population Growth

• Generation / doubling time
• time required for a complete fission cycle
• Length of the generation time is a measure of the
  growth rate of an organism
• Some bacteria species a population can grow from
  a small number of cells to several million in
  only a few hours!!

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Growth Curve

• Predictable pattern in the population of an
  organism over time
• Four phases
• Lag phase
• Initial stage with little growth
• Exponential growth phase
• Period of maximum growth
• Continues as long as cells have adequate
  nutrients and favorable environment
• Stationary phase
• Rate of cell growth equals rate of cell death
• Caused by depleted nutrients and O2, excretion of
  organic acids and pollutants
• Death phase
• As limiting factors intensify, cells die
  exponentially in their own wastes

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Growth Curve
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Other Methods of Analyzing Population Growth

• Turbidity
• Direct microscopic count
• Coulter counting

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Turbidity
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Direct Microscopic Count
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Electronic Counting
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Microbial genetics
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The DNA Code

• Nucleic acids are made of nucleotides
• each nucleotide consists of 3 parts
• a 5 carbon sugar (deoxyribose or ribose)
• a phosphate group
• a nitrogenous base (adenine, thymine, cytosine,
  guanine, and uracil)

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Significance of DNA Structure

• Maintenance of code during reproduction
• Constancy of base pairing guarantees that the
  code will be retained
• Providing variety
• Order of bases responsible for unique qualities
  of each organism

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DNA replication is semiconservative because each
chromosome ends up with one new strand of DNA and
one old strand
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Flow of Genetic Information
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DNA Recombination Events

• Genetic recombination
• occurs when an organism acquires and expresses
  genes that originated in another organism
• 3 means for genetic recombination in bacteria
• Conjugation
• Transformation
• Transduction

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Transmission of Genetic Material in Bacteria
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1. Conjugation

• Conjugation
• transfer of a plasmid or chromosomal fragment
  from a donor cell to a recipient cell via a
  direct connection
• Gram positive and gram negative
• Gram-negative
• cell donor has a fertility plasmid (F plasmid, F'
  factor) that allows the synthesis of a
  conjugation (sex) pilus
• recipient cell is a related species or genus
  without a fertility plasmid
• donor transfers fertility plasmid to recipient
  through pilus
• F and F-

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Physical Conjugation
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2. Transformation

• Transformation
• chromosome fragments from a lysed cell are
  accepted by a recipient cell
• the genetic code of the DNA fragment is acquired
  by the recipient
• Donor and recipient cells can be unrelated
• Useful tool in recombinant DNA technology

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Insert figure 9.23 transformation
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3. Transduction

• Transduction
• Bacteriophage serves as a carrier of DNA from a
  donor cell to a recipient cell
• Two types
• generalized transduction
• random fragments of disintegrating host DNA are
  picked up by the phage during assembly
• any gene can be transmitted this way
• specialized transduction
• a highly specific part of the host genome is
  regularly incorporated into the virus

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Generalized Transduction
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Specialized Transduction
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Transposons

• Special DNA segments that have the capability of
  moving from one location in the genome to another
  
• jumping genes
• Can move from
• one chromosome site to anotherr
• chromosome to a plasmid
• plasmid to a chromosome
• May be beneficial or harmful
• Changes in traits
• Replacement of damaged DNA
• Transfer of drug resistance