Bacteriology - growth curve-lag ,log , stationary, death phase

1. Lag Phase

Characteristics:

Bacteria are metabolically active but not dividing.

They adapt to the new environment, synthesize enzymes, and prepare for DNA replication.

The duration depends on factors like medium composition, inoculum size, and prior conditions of the bacteria.


Growth: No noticeable increase in the number of cells.

Purpose: Physiological adaptation.



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2. Log Phase (Exponential Phase)

Characteristics:

Bacteria undergo rapid cell division at a constant rate.

Growth is exponential: cell numbers double at regular intervals (generation time).

Nutrients are abundant, and metabolic activity is at its peak.

Cells are most uniform in chemical composition, making this phase ideal for biochemical studies.


Growth: Maximum population growth rate.

Purpose: Exploitation of resources.



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3. Stationary Phase

Characteristics:

Growth rate slows as nutrient depletion, waste accumulation, and limited space occur.

The number of new cells equals the number of dying cells, leading to a stable population.

Secondary metabolites, like antibiotics, are often produced in this phase.


Growth: Plateau—no net increase in cell numbers.

Purpose: Survival under limited resources.



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4. Death Phase

Characteristics:

Cell death exceeds cell division due to extreme nutrient depletion and toxic waste accumulation.

Some cells may enter a viable but non-culturable (VBNC) state.


Growth: Decline in population size; some species form spores.

Purpose: Adaptation or termination of the populations

1. BACTERIOLOGY
Unit IV

2. Growth Curve
Bacteria growth can be take place by binary
fission.
Bacterial growth is regulated by nutritional
environment.
When suitable environment, its growth leads to
increase in number of cells.
The growth curve has got four phases:
1. Lag phase
2. Log phase(logarithmic) or exponential phase
3. Stationary phase
4.Decline phase

4. 1. Lag Phase
After inoculation there is normally a brief period of
adaptation.
Bacteria adapt themselves to growth conditions.
It is the period where the individual bacteria are
maturing and not yet able to divide.
During the lag phase of the bacterial growth cycle,
synthesis of RNA, enzymes and other molecules
occurs.
Length of this phase depend on type of bacterial
species, culture medium, and environmental factors.

5. 2. Log Phase:
The Log (Logarithmic / Exponential) phase
There is a rapid period of growth during this phase due
to:
 Bacteria have developed the necessary enzymes and
there are plenty of nutrients.
 There are few waste products being produced.
The rate of cell division is currently at its maximum
with the number of bacteria doubling.
Exponential growth cannot continue indefinitely
Because the medium is soon depleted of nutrients and
enriched with wastes.

6. 3. Stationary phase:
In stationary Phase the rate of growth levels stop
during this period.
This is because:
1. The nutrients are becoming used up.
2. The amount of waste produced by the bacteria
themselves is increasing.
3. The rate at which new cells are produced is
equal to the rate at which other cells are dying.

7. 4. Death (Decline) Phase:
During this phase more bacteria are dying than
are being produced.
This is because:
1.Very few nutrients are left.
2. Many bacteria are poisoned by the waste
produced by such large numbers
3.Finally, after certain time period all the cells die
and culture becomes sterile.

8. Batch Culture
Batch fermentation is a 'closed system‘
The substrate and producing microorganism are
added to the system at zero time and are not
removed until the fermentation is complete.
Nothing added to or removed from the fermenter
during the process
This is simplest and most commonly employed
method of fermentation for the production of
enzymes
 

9. In a batch fermentation process, all the ingredients
are combined at once, and then undergo reaction
without any further input from outside.
This type of Culture goes through three phases
Lag phase - where the microbial cells adapt to the
environment
Exponential phase - where the cells grow in size
 Stationary phase - where all the nutrients have been
consumed – Product formed and the cells die.
 It is used in industries for the production of enzymes
and bread.

10. Batch fermentation has the advantages
 Low investment costs
Simple control & simple operations
Easy-to-maintain complete sterilization.
Seed culture is needed for each new batch.
Bio-ethanol from corn in the USA is almost
entirely produced using batch fermentation.

11. Batch Culture

12. Batch Culture

13. Synchronized culture
 Synchronized culture is a microbiological culture or
cells that are all in the same growth stage.
 Since numerous factors influence the cell cycle
 Obtaining a culture with a unified cell-cycle stage is
very useful for biological research.
 Since cells are too small for certain research
techniques

 synchronous culture can be treated as a single cell; the
number of cells in the culture can be easily estimated,

14. Synchronous Culture

15. Synchronous cultures can be obtained in several ways:
 External conditions can be changed, so as to arrest
growth of all cells in the culture, and then again to
resume growth.
 The newly growing cells are now all starting to
grow at the same stage, and they are synchronized.
(Ex) For photosynthetic cells light can be eliminated
for several hours and then re-introduced.
Another method is to eliminate an essential nutrient
from the growth medium and later to re-introduce
it.
Cell growth can also be arrested using chemical
growth inhibitors. [ Inhibitor can be easily removed
from the culture and the cells then begin to grow
synchronously.] (Ex) Nocodazole

16. Synchronous Culture