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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
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Classification of microbes based on sources of nutritional requirements (Slide 3)
- CARBON SOURCE:
- Autotrophs: CO2 sole or principal biosynthetic carbon source
- Heterotrophs: Reduced, preformed, organic molecules from other organisms
- ENERGY SOURCE
- Phototrophs: Light
- Chemotroph: Oxidation of organic or inorganic cmpnds
- ELECTRON SOURCE
- Lithotrophs: Reduced inorganic molecules
- Organotrophs: Organic molecules
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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Some environmental factors that influence growth (Slide 14)
Osmotic conc, pH, temperature, oxygen levels, pressure
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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
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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
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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)
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