Flashcards in Bacterial Growth Curve Deck (26)
The definition of growth
1. increase in cell size
2. increase in cell numbers leading to overall increase in biomass
what is the most widely used measure of bacterial growth?
to determine the number of cells at any given moment
what two techniques can be used to determine the number of cells?
1. plate count technique
2. spectrophotometric method
limits of plate count technique?
is able to measure a very small number of cells per ml
when to use spectrophotometric method?
requires >100,000 cells per ml and is easier to use
How does growth begin?
begins with a cell adjusting to a new environment and new nutrients
What happens to a cell before cell division when it begins adjusting to its new environment?
it expresses enzymes
and increases in size
what is a lag phase of growth?
This is the initial growth phase where bacterial concentration is low
There are plenty of nutrients so the bacteria are actively synthesizing proteins and they are growing quickly
The cell divisions occurs a little more rapidly and the next faster yet.
What is exponential/log phase?
Bacterial cell density is high and the nutrient levels are still high enough to support rapid growth here.
The division rate here will reach a constant.
Why is it called exponential/log phase?
each cell divides into two, thus the number of cells increases exponentially
What is stationary phase?
bacteria are at a very high cell density and the nutrients have been mostly used up.
the decline in nutrients/increase of metabolic products results in the division rate slowing down.
This causes the cell number to reach a constant.
this constant number may be the result of an end of division altogether
NUMBER OF CELL DEATHS = NUMBER OF NEW CELLS FORMED
the cell number may remain stable for a long time with only a slow decline
What is death phase?
cell number declines exponentially.
True or false, cell numbers decline to zero
False, it rarely does
why is it useful to calculate teh rate of growth during the exponential phase?
because this is the most reproducible measure of the bacterial response to the environmental conditions
What is generation time and which phase is this in?
Cells divide at a constant interval and its in the exponential phase.
What does the length of the interval of the generation time depend on?
1. bacterial species
2. type of medium
What is generation time also known as? why is it called that? give an example
doubling time; because the population of cells doubles over one generation. for example, one cell of E.coli placed in a complex medium will divide every 20 minutes. after 1 hour of growth, (three generations) that one cell will have become Eight. ( 1->2 2->4 4->8).
how would a linear increase of division occur?
if the increase in cell number over time rose by a fixed amount after every generation
how to calculate for the number of generations that an exponential culture undergoes in a given time period?
n = log10(Nt - No)/0.301
No = number of cells at start of the period
Nt= number of cells at the end of the period
Limits of exponential growth?
exponential growth occurs only for a short period when all nutrients are in full supply and the concentration of waste products has not become a limiting factor
What can the rate of exponential growth be expressed as
it can be expressed as the mean growth rate constant (k)
Which is the number of generations per unit time
True or false: we need to know the generation time to calculate the mean growth rate constant
False we dont need to know it
What do we need to know to calculate the mean growth rate constant?
1. the number of organisms at time zero (No)
2. number of organisms after incubation time (Nt)
Formula to calculate the mean growth rate constant?
k = n/t = (log10Nt - Log10No)/0.301t
How to calculate for the mean generation time? (g) in hours