Growth of Microorganisms

1
Growth of Microorganisms

• The Growth Curve

2
The Growth Curve
3
The Growth Curve
4
The Growth Curve

• A plot of log10 (number of organisms) against
  time for a growing culture results in a
  predictable pattern.
• The log value is used as it is easier to plot
  onto a graph.

5
The Growth Curve

• Lag phase
• Short period immediately after inoculation
• Organisms are synthesising the enzymes needed to
  exploit the new medium.
• Cells may grow in size but not usually in number
• (If organisms have been transferred from an
  identical medium, at the same temperature, the
  lag phase may be very short).

6
The Growth Curve

• Exponential phase (log phase)
• Organisms have started to reproduce
• Abundant food, absence of competition and of
  inhibiting factors such as toxic waste products
  allows cell division to occur at a high rate.
• The population doubles at regular intervals.

7
The Growth Curve

• Plotted as arithmetic numbers of cells, the log
  phase would be a curve of ever increasing
  gradient plotted as log10 of cell numbers, it
  gives a straight line.

8
The Growth Curve

• Stationary phase
• In a closed culture food soon runs out or the
  organisms become poisoned by their own
  accumulated wastes
• As a results growth slows down and stops.
• If the population is being measured by a total
  cell count, or by turbidity readings, there may
  be no apparent further change.

9
The Growth Curve

• Death phase
• A viable count will soon show a decline in cell
  numbers as cells die
• This will continue until there are no living
  cells left..