Lecture 18 Microbial Growth Flashcards
Microbial growth
an increase in the number of cells, not cell size
What bacterial growth occurs through
binary fission
Steps of binary fission
- cell elongates & DNA is replicated
- cell wall and plasma membrane constrict; DNA gets pulled to two ends
- cross-wall forms, completely separating the two DNA copies
- cells separate
True or False: bacterial cells can age
TRUE
Four stages of bacterial growth
lag phase, log phase, stationary phase, and death phase
Lag phase
intense preparation for population growth with NO increase in population
Log phase
exponential/logarithmic increase in population
Stationary phase
period of equilibrium; deaths equal to production of new cells
Death phase
population decreases at a logarithmic rate
Growth phase with a highly variable length
lag phase
Growth phase with a short length
log phase
Best growth phase for experiments
log phase (cells are most active)
What occurs inside the cell during the lag phase
adaption to new medium; re-synthesis of damaged cell constituents; turning genes on/off
calculation to determine the number of bacteria in the fifth-generation
2^5 = 32
Why do we graph in log instead of exponential?
better representation; fits the graph better as exponential gets too large too quickly
During what growth stage are endospores produced?
stationary phase
What is growth limited by during the growth stage?
nutrient availability, toxic metabolites, and limited space
Dying cells =
dividing cells (viable count doesn’t change)
True of False: generation time varies by species of bacteria
TRUE
Generation time
the time it takes a bacterium to do one binary fission (aka doubling time)
Formula to calculate the number of generations a culture has undergone
log # of cells (end) - log # of cells (start) / 0.301
Formula to calculate the generation time for a population
hrs x 60 min/hr / number of generations
Three methods used to measure growth
direct microscopic count, turbidity measurement, viable cell count
Drawbacks of direct microscopic count
doesn’t distinguish dead and live cells, difficult to see small and unstained cells, labor intensive, difficult to count motile bacteria
