microbial growth Flashcards
how do microbes reproduce
binary fission
describe the process of binary fission
cell elongates and DNA is replicated, inward growth of PM and cell wall, septum divides the cell in two, cells separate
other than binary fission, what are some other reproductive strategies for microbes
budding, multiple fission, and exospore production
in what conditions is a bacterial growth curve produced
when cultures are grown in liquid medium in a closed culture system (ie when we don’t supply it with fresh medium)
what are the 5 phases of the bacteria growth curve
lag, log/exponential, stationary, death, long-term stationary
describe any changes in cell number during the lag phase
there is no change in cell number
how long is the lag phase + what affects the length
may be long or short depending on the bacterial species, the history of the culture, and the growth conditions
when might you have a short lag period
if you subculture your cells into a new tube with the same medium it was already using
when might you have a long lag period
if you use an old/injured culture to start, or if you subculture it into a different medium than it was already using
what happens in the exponential phase
lots of bacterial growth
describe the growth in the exponential phase
growth is constant (ie doubles)
how will you get a linear relationship when plotting the exponential phase
plot Log10 number of cells vs time
T or F: in the exponential phase, the bacterial is very sensitive to adverse conditions
true
why is bacteria the most sensitive to adverse conditions in the exponential phase
because they’re the most metabolically active during this phase so many processes are happening at once
describe the growth rate in the stationary phase
growth rate slows down (curve becomes horizontal)
why does the exponential phase stop
nutrients may be lacking, limited space, changes in pH, oxygen solubility
describe the growth rate during the death phase
number of viable cells declines at an exponential rate
describe the growth rate during the long-term stationary phase
number of viable cells remains constant, but there are waves of population sizes
why are there waves of new populations during the long-stationary phase
some bacteria can withstand the flask conditions, but then the conditions change and they decrease, but then a new pop. will adapt, and so on
what is generation time
the time it takes for one cell to divide in two
describe two ways we can plot data to determine generation time
- absorbance vs time
- Log10 number of cells vs time
what machine is used to plot absorbance vs time to determine generation time
spectrophotometer
how do we plot absorbance vs time using a spectrophotometer
inoculate and incubate a culture, take out an aliquot at each time point, then measure the absorbance at each time point
at what phase of the bacterial growth curve can we measure generation time
during the exponential phase ONLY
how do we determine generation time from a graph of absorbance vs time (ie what formula do we use)
t(Afinal) - t(Ainitial)
other than generation time, how can we measure bacterial growth
by using the growth rate constant
what letter denotes the growth rate constant
k
what does the growth rate constant equal to
= number of generations per unit of time
formula for growth rate constant?
k = 1/g (g=generation time)
what are the units of k (growth rate constant)
of generations per hour
