Download - Lecture 8 - Bacterial Growth
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Siti Norbaizura bt Md ZainApplied Science Faculty, UiTM
Lecture 8 02/09/09
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Bacterial Growth Definition
Vegetative growth Cells actively growing and dividing
Microbial growth Population growth as opposed to cell growth Measured by total number of cells
Exponential due to binary fission reproduction
The increase in number of cells, not cell size
Generation time (or doubling time) The time for an individual or a population to double
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Binary fission
Budding
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The bacterial chromosome is duplicatedshortly before binary fission begins.
The duplication usually occurs by the rollingcircle mechanism taking place at the cellmembrane.
The duplicate chromosomes attach to the cellmembrane, which grows and separates thechromosomes.
At this point, the bacterium contains twochromosomes in regions known as nucleoids.
The chromosomes separate, and the cell walland cell membrane begin to form a septum.
The septum becomes complete and the twonew daughter cells separate.
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In yeast, DNA duplication occursand a new cell develops at thesurface of the existing cells
This small cells gathers cytoplasmand organelles (if a eukaryotic cell)and develops and breaks free from
the parent cellThe reproductive process is calledbudding
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Binary Fission
Generation Time (Doubling Time) time required for a cell to divide
most about 1 Hr. To 3 Hrs.E. coli - 20 minutes
Mycobacterium tuberculosis - 24 Hrs.
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E. coli - generation time of 20 min. 20 generations (about 7 hrs.)
1 million cells
30 generations ( about 10 hrs.) 1 billion cells
72 generations ( about 24 hrs.) 1 x 1021
1,000,000,000,000,000,000,000 cells
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If 100 cells growing for 5 hours produced1,720,320 cells:
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Direct methods
Plate counts Filtration MPN Direct microscopic
count Dry weight
Indirect methodsTurbidity Metabolic activity Dry weight
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Plate counts: Perform serial dilutions of a sample
Figure 6.15, step 1
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Inoculate Petriplates fromserial dilutions
Figure 6.16
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Filtration
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Direct microscopic count
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Turbidity
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Bacterial GrowthBacterial Growth
Four phases of growth in a culture
Lag phase
Log phase (or exponential phase)
Stationary phase
Death phase (or decline phase)
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Will encompass several hoursDuring this time the organisms grow in
size, accumulate organic matter andstore large quantities of chemicalenergy such as ATP for biosynthesis
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Microorganisms undergo rapid cell divisionand fulfill their generation time.
The population doubles during eachgeneration time
The population increases in size at alogarithmic or exponential rate Rapid cell growth (exponential growth) population doubles every generation microbes are sensitive to adverse
conditions antibiotics
anti-microbial agents
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During the third phase of a populations history,the rate of cell division decreases and the oldercells begin to die.
During this phase, the number of living cells inthe population remains constant.
Death rate = rate of reproduction cells begin to encounter environmental stress lack of nutrients lack of water not enough space metabolic wastes oxygen pH
Endospores would form now
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During the fourth phase, the death/declinephase, the environment has become difficultfor living and the rate of cell death exceedsthe rate of cell division.
The population declines in numbers and thepopulation may completely die out if theenvironmental stresses are not reversed.
Death rate > rate of reproduction Due to limiting factors in the environment
G ti ti D bli ti
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Generation time = Doubling time
Step 1: Get your growth
curve (straight line with 3points).
Step 2: Pick any pointabove your time zeroreading. Follow across to
intersection of growthcurve then down to time.Record this time.
Step 3: Double thenumber you picked instep two and repeat steptwo.
Step 4: subtract time 1from time 2 = Doubling
time.