Lecture 8 - Bacterial Growth

8/2/2019 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.

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Lecture 8 - Bacterial Growth