MCB 2610 Exam 2 Questions And Correct
Answers.
Cultivation independent methods - answerDNA from unculturable bacteria can be amplified
and sequenced by PCR
Sequences can be used to produce fluorescent probes that will bind to complementary DNA
(Fluorescent In Situ Hybridization FISH)
FISH - a...
Cultivation independent methods - answer✔✔DNA from unculturable bacteria can be amplified
and sequenced by PCR
Sequences can be used to produce fluorescent probes that will bind to complementary DNA
(Fluorescent In Situ Hybridization FISH)
FISH - answer✔✔Cells fixed in place
Fluorescently labeled probes consisting of 165 rRNA gene sequence sent to attach to RNA
View in Epifluorescence microscope
Metagenomics - answer✔✔DNA is isolated from an environmental sample and sequenced
Metagenomic information must still be confirmed in cultured organisms
Microbial consortia - answer✔✔Microbes that can't grow on their own
Direct counts - answer✔✔Load known volume into gridded slide
Count under a light microscope
Flow Cytometry - answer✔✔Microbial suspension forced through small orifice with a laser
beam
Movement of microbe through orifice impacts electric current that flows through orifice
Instances of disruption of current are counted
Specific antibodies can be used to determine size and internal complexity
Spread plate technique - answer✔✔used to get a living (viable) cell count
Small amount of sample is pipetted onto a solid medium then spread around that medium
Measured in CFU colony forming units
Pour Plate - answer✔✔Original sample is diluted multiple times and the most dilute ones are
poured into a plate with liquid agar
Calculating CFU/mL - answer✔✔Average cell number / (dilution X volume plated)
What if cells are already very diluted? - answer✔✔A filter apparatus can concentrate cells
Sample is filtered through a membrane filter then the contents that don't go through are
transferred to a medium and incubated
Turbidity - answer✔✔Spetrophotometer sends light through a liquid culture
If the tube is cloudy, light wont reach the other side because it will hit all the bacteria in the tube
This can give a rough estimate of cell density in the tube
Higher absorbance = higher population in culture
Indirect measurements of cell mass - answer✔✔Dry weight - time consuming and not very
sensitive
Quantity of particular cell constituent - DNA protein ATP
Growth - answer✔✔Population growth vs growth of actual cells
Growth Curve - answer✔✔Observed when microorganisms are cultivated in batch culture
(closed culture)
Usually plotted as a logarithm of cell number vs. time
Has 4 distinct fases
Lag phase - answer✔✔Cell synthesizing new compounds
ex. to replenish spent materials, adapt to new conditions or medium
Exponential phase - answer✔✔Rate of growth and division is constant and maximal
Population is most uniform
Stationary phase - answer✔✔Closed system
Population growth eventually ceases
Reasons - nutrient limitation, limited oxygen availability, toxic waste accumulation - can make
environment too acidic
Stationary phase and starvation response - answer✔✔Activate survival strategies:
Morphological changes - endospore formation, decrease in size
Senescence and Death Phase - answer✔✔Number of viable cells declines exponentially
Two alternative hypotheses:
Cells are viable but not culturable (VBNC) - cells alive, but dormant, capable of new growth
when conditions are right (programmed cell sterility)
Programmed cell death - fraction of the population genetically programmed to die so other cells
can live off their nutrients
Prolonging of Death phase - answer✔✔Death phase is not dramatic - population slightly
increases or decreases based on conditions in environment - toxins released by dying cells or
nutrients released by dying cells
Balanced Growth - answer✔✔Cellular constituents manufactured at constant rates relative to
each other
Unbalanced Growth - answer✔✔Rates of synthesis of cell components vary relative to each
other
Occurs under a variety of conditions - shift up (poor to rich medium) shift down (rich to poor
medium)
Demonstrates that microbial growth is under precise coordinated control and that organisms
respond quickly to changes in environmental conditions
Measuring microbial population growth - answer✔✔Generation time - time to double the
population in the exponential phase
Growth rate - number of generations/unit of time (inverse of generation time)
Growth yield - the maximum population density and/or amount of cellular material produced by
the culture
Generation time - answer✔✔time required for a population to double
varies depending on microorganism and environmental conditions
10 minutes for some bacteria days for some eukaryotic microorganisms
The continuous culture of microorganisms - answer✔✔Growth in an open system
Maintains cells in log phase at a constant biomass concentration for extended periods
Achieved using a continuous culture system
No stationary phase - allow exchange of media and removal of toxic waste
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