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37 Cards in this Set
- Front
- Back
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Define microbial growth
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def: Growth of a population - an increase in the number of cells
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What is doubling time?
Cells in a culture do not have the same doubling time. G D P 2 new |
Period of time required for cells in a microbial population to GROW, DIVIDE and PRODUCE 2 new cells for each one that existed before.
Tells us how fast a population is growing. Average doubling time of all the cells in the culture. |
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Why is Growth Rate used to describe doubling time?
def: Doubling times per hour |
A LOW VALUE(small amount of of doubling time)=RAPID/FAST growth.
HIGH VALUE of doubling time= SLOW GROWTH |
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How do microorganisms grow exponentially?
# of cells per millileter of culture growing exponentially with a doubling time of 20 min. |
# of doublings
1,2 Min 0,20 Numbers 1000,2000 Scientific Notation 10*3,2X10*3 Logarithm 3.0, 3.3301 |
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Phases in a growth culture
L E S D |
Lag Phase= When cells prepare to grow
Exponential Phase= When cell numbers double at regular intervals Stationary Phase= When growth ceases Death Phase= When numbers of live cells decline |
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What is lag phase?
Cells are preparing to grow Lag phase depends on length of time cells were in stationary or death phases |
Follows innoculation of stationary- or death phase cells into a fresh culture medium. There is a no-growth period, but there is metabolic activity.
Move from poor to rich environment = NO LAG |
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Why can't the exponential phase continue forever?
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b/c nutrients become depleted or toxic products accumulate
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What happens to cells in the stationary phase?
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1. No net increase of mass(growth)
2. cells become smaller 3. Synthesize components that help them survive non-growth periods |
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Why do cells enter the death phase?
How quickly do they die? |
Death usually occurs b/c a cell has used all of its intracellular reserve of ATP.
Cells die exponentially much slower than they grew in the log phase. |
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How do you maintain a continuous culture in the laboratory?
3 |
1. Maintain the concentration of 1 nutrient low enough to limit growth rate.
2. Add nutrients, including the limiting nutrient. 3 Remove cells and end products continuously |
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How does the concentration of limiting nutrient effect the culture.
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It sets the rate of growth of the culture to the rate of loss of cells through the overflow.
Growth rate exceeds Loss Rate = Population increase and limiting nutrient is used up which makes cells stop growing so fast b/c they need the nutrient |
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Define colony
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def: Complex (mass of cells)in a mixture of cells in different phases of growth.
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How does location in a colony affect a cell's phase of growth?
How does location affect its access to oxygen? |
On the surface(edge)= AEROBIC
EXPONENTIAL(growing)have nutrients. In the center = ANAEROBIC/STATIONARY or DEATH No access to nutrients |
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What are nutrients?
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def: Chemicals from the environment that a cell needs to grow.
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Nutritive growth requirements
Carbon Oxygen |
Carbon=Structural basis of biochemicals.
Oxygen=Microbial metabolism 3 areas 1. Nutrient 2. Electron acceptor 3. Generator of toxic products Micoo capable of aerobic respiration use oxygen gas to generate energy |
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Nutritive growth requirements
Nitrogen Sulfur Phosphorus |
Nitrogen=Constituent of proteins / nucleic acids/ metabolites.
Sulfur= Component of 2 amino acids/few types tRNA Phosphorus=nucleic acid/phospholipids(membranes) |
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Nutritive growth requirements
Growth Factors Trace elements |
Growth Factors= Essential compounds required for growth
Amino acids/GATC. Some bacterial can synthesize them. Grow faster if provided. Ribosomes increase in #. Trace elements= Coenzymes= organinc molebules an enzymen need to be active Cofactors= ions an enzyme needs to be active. |
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Toxic oxygen
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def: contains compounds that are by-products of aerobic metabolism.
1. Hydrogen peroxide Free radicals 2. superoxide 3. Hydroxyl radical |
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What is a rich growth environment?
How do micoo exploit a rich growth environment? |
The major elements
Carbon, Oxygen, Nitrogen, Phosphorus, Sulfur, Trace Elements, Growth Factors If growth factors are present micoo will use them even if they are capable of making their own. |
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What are the significant physical factors in a micoo nonnutrient environment?
Chemical factors? |
Temperature
Hydrostatic Pressure pH Osmotic strength |
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Minimum temperature of growth
Maximum Optimum What determines the max and minimum temperatures? |
Lowest temp that will support growth.
Highest that will support growth Temperature at which the micoo grows most rapidly usually few degrees below max The heat stability of an organism's proteins. |
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Thermophile
Mesophile Psychrophiles/ psychotroph |
Above 50 degrees
37 degrees human body temp At or below 5 degrees refrig. |
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Obligate Psychrophiles
Facultative Phsychrophiles |
Cannot grow at or above 20 d
Cold ocean water Can grow above 20 d Soil and water |
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Facultative Thermophiles
Stenothermophiles Extreme Thermophiles |
Can grow below 37 d soil
Cannot grow below 37 d Compost Grow above 80/100 d hot springs |
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What is hydrostatic pressure?
Why can micoo withstand high hydro/pressure? How is hydro/pressure harmful? |
def: Pressure applied to a liquid measured by atmospheres
Does not crush b/c water passes readily through the cell membrane. The pressure inside/outside the cell is equalized. High pressure inhibits chemical reactions that increase molecular volume. |
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What pH levels do bacteria(prokaryotes)prefer?
Fungi? Acidophiles Alkaliphiles Algae/Protazoa |
B. Slightly alkaline
F. Slightly acidic Acid-(acid lovers) thrive in low pH Alka-(base lovers)thrive in high pH Neutral pH |
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How can bacteria exist in enviroments with a wide range of pH?
Range higher than their proteins can tolerate- |
They adjust their intracellular pH by pumping hydrogen ions out or into the cell. They always maintain their internal pH.
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How are halophiles unlike most other bacteria?
How do most bacteria maintain turgor pressure? What is plasmolysis? |
Instead of high osmotic strength preventing growth(bacteria) Halophiles(salt lovers)flurish in water that is saturated in salt.
Pumps potassium ions and/or osmoprotectants into the cell. def: High external osmotic strenght draws water out of the cell, shrinking the cytoplasm |
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Difference btwn total count
and viable count? |
Total count= Contains both live and dead cells(use a Petroff-Hauser counting chamber)
Viable count= Only live cells depends on a cell's ability to grow to form a colony or development of a turbid culture |
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Measuring Mass Dry Weight
Measurement? Advantages? Disadvantages? |
Seperate cells from medium/dry
by centrifugation Mass of cells Sets standard for turbidity test Tedious, time-consuming, insensitive |
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Turbidity
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Measured w/ spectormeter which measures how much light a liquid culture of cells transmits.
Easy Not highly sensitive |
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Metabolic activity
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Rate of formation of metabolic products
ie. gases, acids, Rate of utilization of a substrate ie. oxygen or glucose Rate of reduction of certain dyes |
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Direct microscopic
electronic count |
Counting cells within several squares and averaging the results
Unable to distinguish btwn live/dead cells/ slow process Coulter counter=cells do not conduct electricity as much as the medium-cell goes through a pore and conductivity of the circuit decreases.Expensive equipment needs no foreign particles. |
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Plate count
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Sample of culture is diluted tenfold/hundredfold
Spread or poured on plate Plates btwn 30-300 colonies selected and counted |
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Most probable number (MPN)
A single live cell can develp into a turbid culture |
Several tenfold dilutions, tubes are incubated. Tubes that become cloudy have one or more cells. Number of micoo that were most probably present in original sample computed using MPN table.
eg. 5 3 1 MPN 11.0= 11,000 cells per millileter |
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If you wanted to know how many dead cells were in a culture, what would you do?
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Using a microscope use a vital stain whch can be used to distinguish live cells from dead ones.
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If you wanted to make cells in a chemostat grow more rapidly, what would you do?
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Increase the concentration of the limiting nutrient
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