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Flashcards in lecture 1.9 Deck (20):

What does growth mean?

Growth refers to population growth rather than growth of individual cells


Describe the lag phase

to replenish spent materials
to adapt to new medium or other conditions


Describe the exponential phase?

Also called log phase
Rate of growth and division is constant and maximal
Population is most uniform in terms of chemical and physical properties during this phase


What is balanced growth?

culture conditions need to be essentially constant.
this is an ideal situation
What balanced growth means is that ALL cellular constituents are manufactured at constant rates relative to each other


Generation time=

time required for the population to double in number


Exponential Growth rate=

How fast cells grow in exponential phase


Cell (biomass) yield=

How many cells are produced in a particular culture


why does unbalanced growth happen?

shift-up (poor medium to rich medium)
shift-down (rich medium to poor medium)
change in environmental conditions


Stationary phase=

total number of viable cells remains constant
active cells stop reproducing or reproductive rate is balanced by death rate


What are the reasons for stationary phase?

Nutrient limitation
Limited oxygen availability
Toxic waste accumulation
Critical population density reached


What are some of the responses a cell takes when stressed during the stationary phase?

morphological changes (endospore formation)
decrease in size, protoplast shrinkage, and nucleoid condensation
In E. coli and related bacteria, RpoS protein assists RNA polymerase in transcribing genes for starvation proteins


Describe starvation responses/starvation protiens

increase cross-linking in cell wall
Dps protein protects DNA
chaperone proteins prevent protein damage
increased resistance to stresses: UV, heat, acid pH, high osmolarity, reactive oxygen species
long-term survival
increased virulence


What are the two theories/responses of "death phase"

cells alive, but dormant, capable of new growth when conditions are right
Programmed cell death
fraction of the population genetically programmed to die (commit suicide)


How do you directly count cell numbers

counting chambers
electronic counters – flow cytometry
on membrane filters


How do you do a direct count on membrane filters?

Cells filtered through special membrane that provides dark background for observing cells
Cells are stained with fluorescent dyes
Useful for counting bacteria
With certain dyes, can distinguish living from dead cells


How do you count with flow cytomerty?

Microbial suspension forced through small orifice with a laser light 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


How do you use spread and pour plate to do direct cell counts?

diluted sample of bacteria is spread over solid agar surface or mixed with agar and poured into Petri plate
after incubation the numbers of organisms are determined by counting the number of colonies multiplied by the dilution factor
results expressed as colony forming units (CFU)


What are the three ways you can count by cell mass?

Dry weight
Quantity of a particular cell constituent
e.g., protein, DNA, ATP, or chlorophyll
Turbidometric measures (light scattering



Rate of incoming medium = rate of removal of medium from vessel
An essential nutrient is in limiting quantities



regulates the flow rate of media through vessel to maintain a predetermined turbidity or cell density
dilution rate varies
no limiting nutrient
turbidostat operates best at high dilution rates