EXAM 2- Chapter 7- part 3 Flashcards
What does growth refer to?
population growth rather than growth of individual cells
Cells can grow in what kinds of systems?
open or closed
When is growth curve observed?
When microorganisms are cultivated in batcch culture
Closed system
Four phases of growth curve
lag phase
exponential/log phase
stationary phase
death phase
What is the growth curve?
graphical representation of the change in bacterial population size over time
Semi-log graph
Lag phase
cell synthesizing new components
replenishes spent materials and adapts to new environment
Log phase
rate of growth and division is contant and maximal
What phase is population most uniform?
log phase
Stationary phase
population growth eventually stops in a closed system
rate of division=rate of death
What are the reasons for stationary phase?
nutrient limitation
oxygen availability
toxic waste accumulation
Death phase
number of viable cells declines exponentially
logrithmic death
Starvation response- stationary phase
cells activate survival strategies to remain in stationary phase
What are strategies used to remain in stationary phase?
morphological changes
Rpos protein assists RNA polymerase in transcribing genes for starvation proteins
starvation proteins
bind to different macromolecules to prevent damage
What are morphological changes associated with starvation response?
endospore formation
decreasing in size- smaller cells require less nutrients
express flagella- can move to find new food source
What triggers sporulation?
nutrient deprivation
What are hypothesis for why some cells do not die in death phase?
Viable but not culturable
programmed cell death
Viable but not culturable (VBNC)
cells are alive but dormant
can resuscitate upon change in environment/correct conditions
Programmed cell death
fraction of the population is genetically programed to die
When cells die they release things that remaining cells can use
Why are VBNC cells problematic?
assays tend to be based on ability to culture
VBNC can be problematic for assays used for food contamination- contamination can go unnoticed
Prolonged stationary phase
prolonged decline in cell numbers
takes place after traditional death phase
Get waves of increasingly adapted cells
How long can cells hang out in prolonged stationary phase?
months to years
Balanced growth
have everything they need in perfect timing
cellular constituents manufactured at constant rates
Example of balanced growth
log growth
Unbalanced growth
rate of synthesis of cell components vary relative to each other
When does unbalanced growth occur?
change in nutrient level
T/F cells can shift back to balanced growth
TRUE
once cells adjust to change in environmental change they can shift back
Unbalanced growth: Shift-up
poor medium to rich medium
What happens to growth during a shift up?
undergoes a period of log growth but faster
Unbalanced growth: shift-down
rich medium to poor medium
What happens to growth during shift down?
undergoes period of log growth but slower
What does unbalanced growth demonstrate?
Microbial growth is under precise coordinated control
Microorganisms respond quickly to changes in environment
What are 3 things we can find using growth curve?
generation time
growth rate
growth yield
Generatio time/ doubling time
the time to double the population during exponential phase
Growth rate
number of generations per unit of time
slope of the line
growth yield
maximum population density/the amount of cellular material produced
How to calculate doubling time?
- look at the number of cells: want to find points where cell count doubles
- look at time of first number and time of second (doubled) number
- difference between the two is generation time
What is the importance of a semi log scale
linear scale will not make log phase obvious
semi-log allows exponential phase to be a straight line
makes it easier to find slope
What is continuous culture and what does it do?
growth in an open system
maintains cells in log phase at a constant biomass concentration for extended periods
Two types of continuous culture systems
Chemostat
Turbidostat
What is the importance of continuous culture?
Can study growth at very low nutrient concetration
Study interactions under conditions resembling aquatic environments
Food and industrial microbiology- can exploit and harvest byproducts
Closed system
nothing else is being added or remove
has four phases of growth
Open system
maintians log phase for extended periods
Chemostat
rate of incoming medium= rate of removal
Flow rate is set constant
1 essential nutrient is kept at limited quantity
What keeps chemostat system in steady state?
1 essential nutrient kept at limited quantity
Turbidostat
photocell- regulates the flow rate of media to maintain a predetermined turbidity
No limited nutrients- all in excess
Dilution rate varies
What keeps turbidostat in log phase?
variation of dilution rate to keep predetermined turbidity
T/F turbidostat operates best at low dilution
FALSE- best at high dilution
If absorbance is too high machine will increase dilution
opposite for low absorbance
