Microbiology Module 3

  1. Microbial Nutritional Requirements Overview (Slide 2)
    Source of carbon precursor molecules w/electrons that are either already hi-energy or can be energized.

    Movement of hi energy electrons leads to production of ATP and/or proton motive force (PMF)

    Sources of nitrogen, sulfur, phosphorous, iron and others also required to make all cellular bldg blocks from precursors

    Microbes vary in ways in which they obtain nutritional requirements. Used in classification
  2. Classification of microbes based on sources of nutritional requirements (Slide 3)
    • Autotrophs: CO2 sole or principal biosynthetic carbon source
    • Heterotrophs: Reduced, preformed, organic molecules from other organisms

    • Phototrophs: Light
    • Chemotroph: Oxidation of organic or inorganic cmpnds

    • Lithotrophs: Reduced inorganic molecules
    • Organotrophs: Organic molecules
  3. Prokaryotic Transport Systems (Slide 5)
    Uptake of nutrients require special transporters since CM is impermeable to most substances.

    Active transport move solutes into cell against conc. gradient, requires an energy source

    Facilitated diffusion (passive) is not a major mechanism for prokaryotic transport because it requires environment in which conc. of nutrients is higher outside the cell relative to inside
  4. Gradient-Driven Active Transport (Slide 6)
    Cells use energy from electron transfers to generate gradients (respiration) and then use gradients for active transport

    Symport (Sugars, amino acids, anions) occurs when H+ or Na+ and solute both move into cell together

    Antiport occurs when H+ and another cation are transferred in opposide directions

    • NOT used by "fermenting" microbes
    • (cannot generate ion gradients)
  5. ABC (ATP-Binding Cassette) Transporters (Slide 7)
    Sugars, amino acids and many other things transported using this mechanism

    Contain nucleotide binding domain

    Many related ABC transporters all use ATP as driving force but differ in which solute-binding proteins (Periplasmic binding proteins) interact with the membrane-spanning channel
  6. Group Translocation (Slide 8)
    Mechanism for transporting sugars into the cell

    Also called Phosphoenolpyruvate Sugar Phosphotrasferase system (PTS)

    Transported sugar is phosphorylated as soon as it reaches the cytoplasm, sugar-P cant get back out. PEP is initial energy source

    Fermentative bacteria that cannot use symport can use these systems
  7. Measuring Microbial Growth (Slide 9)
    Refers to the determination of number of cells within a population

    Direct methods use microscope to count individual cells (Petroff-Hausser counting chamber)

    Plating techniques count live cells after each cell in a culture has grown to form a colony on an agar plate

    Total conc. of cell mass is measured using a spectrophotometer to assess light scattering

    Growth curves are obtained and used to generate growth rates and doubling times under diff. environmental conditions. Used for Classification
  8. Counting Chamber (Slide 10)
    Microbes can be stained prior to counting

    Requires a microscope and special slides with grids

    Immediate answers can be obtained

    Both lives and dead microbes are usually counted
  9. Turbidity measurements use spectrophotometer (Slide 11)
    Microbes in a culture scatter light and amount of scattered light is a measure of total cellular mass

    Rapid and common technique that is used when a culture must be manipulated at a given cell density during its growth
  10. Dilute and Plate (Slide 12)
    For counting live cells.

    Takes time and effort. Results in 24-48 hours

    Usually used to verify results from other quicker methods

    Used to measure viability in antibiotic-type experiments
  11. Microbial Growth Curve (Slide 13)
    Usually plotted as log [cells] vs. time

    Lag phase is seen when new cultures are inoculated from non-growing cells

    Log (exponential) phase is used to generate growth rates under diff. conditions

    Stationary approx 10^9 cells/ml, happens when cells stop dividing or when growth is balanced by death

    Death phase may be seen using dilute and plate method
  12. Some environmental factors that influence growth (Slide 14)
    Osmotic conc, pH, temperature, oxygen levels, pressure
  13. Classification of microbes based on growth in diff. environments (Slide 15)
    Osmotolerant: able to grown in wide range of hypotonicity

    Halophiles: Grow best under high levels of salt in environment

    Acidophiles: Love acidic environment

    Psychrophiles: Grow best with very cold condition

    Psychrotrophs: Can grow in cold but prefer warmer temperatures

    Mesophiles: Grow on body temperature

    Thermophiles: 60-80 degrees

    Hyperthermophiles: 80+ degrees

    Obligated aerobe: Need oxygen to grow

    Facultative Anaerobe: Does not require oxygen for growth, but growth is facilitated in the presence of oxygen

    Aerotolerant aerobe: Dont care about having or not having oxygen

    Obligate anaerobe: Requires absolutely no oxygen

    Microaerophiles: Requires small amount of Oxygen

    Barophiles: require high hydrostatic pressures
  14. Microbial life at thermal extremes (Slide 16)
    Life likely evolved at higher temps --> thermophiles (that is the norm environment)

    Enzymes and proteins from thermophiles function in same reactions and in same ways, but a few AA differences allow proteins to remain folded at higher temps

    Higher numbers of specific ionic bonds are important for protein structures in thermophiles and hyperthermophiles

    Ionic bonds independent of temperature for bond strength
  15. Microbial Life at thermal extremes (Slide 17)
    CMs of thermophilic bacteria are high in saturated FAs and hopanoids to maintain integrity of lipid bilayer

    C40 units ether-linked to glycerol phosphate are used by hyperthermophiles (all archaea)

    DNA positively supercoiled in hyperthermophiles

    • Psychrophiles have CMs w/higher numbers of PUFAs and hopanoids to maintain fluidity
    • (negatively supercoiled DNA)
Card Set
Microbiology Module 3
Module 3