bacterial Growth curve and nutrition of bacteria.ppt

The bacterial cell contains water (80% of total weight), proteins, polysaccharides, lipids, nucleic acids, mucopeptides and low molecular weight compounds. For growth and nutrition of bacteria, the minimum nutritional requirements are water, a source of carbon, a source of nitrogen and some inorganic salts.

1. BACTERIAL GROWTH
Roma Goyal

2. Bacterial growth
4-2
Binary fission
Generation time
Phases of growth

3. Binary fission
Figure 4.2
1.Prokaryote cells grow
by increasing in cell
number (as opposed to
increasing in size).
2.Replication is by binary
fission, the splitting of
one cell into two
3.Therefore, bacterial
populations increase by
a factor of two (double)
every generation time.

4. Generation time
4-4
The time required to for a population to double (doubling
time) in number.
Ex. Escherichia coli (E. coli)double every 20 minutes
Ex. Mycobacterium tuberculosis double every 12 to 24
hours

6. Lag Phase: Preparatory phase. Lasts 1 hour to
days. Bact increase in cell size, metabolic
activity, DNA, enzymes.
Log phase: Stage of exponential growth.
Generation time is reduced to minimum. Bact
are susceptible to antibiotics, radiation etc. if
unchecked 1 bact can produce population of
80,000 tons in 24 hrs.

7. Stationary phase: Due to slowing of growth,
increase of wastes, decrease of nutrients &
pH, generation and death equalize. Bact
produce toxins, spores
Stage of decline : Death> birth

8. 1.Bacteria growing in batch cultureproduce a growth curvewith up to four
distinct phases.
2.Batch cultures are grown in tubes or flasks and are closed systemswhere no
fresh nutrients are added or waste products removed.
3.Lag phaseoccurs when bacteria are adjusting to them medium. For example,
with a nutritionally poor medium, several anabolic pathways need to be turned
on, resulting in a lag before active growth begins.
4.In logor exponential phase, the cells are growing as fast as they can, limited
only by growth conditions and genetic potential. During this phase, almost all
cells are alive, they are most nearly identical, and they are most affected by
outside influences like disinfectants.
5.Due to nutrient depletion and/or accumulation of toxic end products,
replication stops and cells enter a stationary phasewhere there is no net
change in cell number.
6.Death phaseoccurs when cells can no longer maintain viability and numbers
decrease as a proportion.
Growth in Batch Culture

9. Mean Generation Time
and Growth Rate
The mean generation time (doubling time) is
the amount of time required for the
concentration of cells to double during the log
stage. It is expressed in units of minutes.
Growth rate (min
-1
) =
Mean generation time can be determined
directly from a semilogplot of bacterial
concentration vstime after inoculation timegeneration mean
1

10. Environmental factors
4-10
Temperature
Oxygen requirement
pH
Water availability

11. Temperature
4-11
Enzymes, the machinery of the cell, are influenced
by external factors and can be shown to have a
range where they function that includes an optimal
value that produces the highest activity.
The range of enzyme activity determines the range
for growth of specific bacteria, analogously leading
to a value for optimal growth rate.
In the case of temperature, bacteria are divided
into categories based on the temperature range
where they can grow and the temperature that
provides optimal growth.

12. Temperature
Psychrophile
0
o
to 18
o
C
Psychrotroph
20°C to 30°C
Important in food spoilage
Mesophile
25°C to 45°C
More common
Disease causing
Thermophiles
45°C to 70°C
Common in hot springs and hot water heaters
Hyperthermophiles
70°C to 110°C
Live at very high temperatures, high enough where water threatens to become
a gas
Usually members of Archaea
Found in hydrothermal vents

13. Oxygen requirements
4-13
• Oxygen is a very reactive molecule and can affect cells in several ways. The effect of oxygen is often determined using
thioglycollate broth, a special medium that contains a reducing agent (thioglycollate) that removes oxygen so that a
gradient occurs within the tube.
• Obligately aerobic bacteriacan obtain energy only through aerobic respiration and have to have oxygen available. Thus,
they will grow only at the surface of thioglycollate broth.
• Obligately anaerobic bacteriadie in the presence of oxygen and can only grow at the bottom of thioglycollate broth.
Some anaerobes are so sensitive to oxygen that even thioglycollate broth is not anoxic enough to provide suitable
anaerobic conditions.
• Microaerophilesrequire oxygen for growth but the 20% in air is too toxic. As a result, they grow near the top but
beneath the surface of thioglycollate broth where the oxygen concentration is typically 4 –10%.
• Facultative anaerobescan use oxygen for aerobic respiration but can switch to fermentative metabolism in the absence
of oxygen. As a result, they will grow throughout thioglycollate broth. (Heavier growth at top.)
• Aerotolerant anaerobesare anaerobic bacteria that can grow in the presence of air. (Not shown in diagram.)

14. pH
4-14
Neutrophiles grow best around neutral pH (7)
Acidophiles grow best at pH < 7
Alkophiles grow best at pH > 7
Acidotolerant grow best at pH 7 but can also grow at
lower pH
Alkotolerant grow best at pH 7 but can also grow at
higher pH

15. Water Activity
Liquid water is essential for life.
Aqueous solutions actually have different amounts of water
available, depending on how many solutes are dissolved in it.
As a very simple model, consider two glasses, one full of pure
water, the other containing the same amount of water plus a
sponge. Which one would be easier to drink? On a much
smaller scale, dissolved solutes act like a sponge, making less
water available.
Water activity (a
w) can be decreased by the addition of any
soluble molecule although salt (NaCl) and sugars are probably
the most common.

16. Water Activity
Microbes that require a high water activity (near or at 1) are
termed nonhalophiles. (Halophile= salt-loving)
Some bacteria require salt to grow and are called halophiles. If a
very high concentration of salt is required (around saturation), the
organisms are termed extreme halophiles.
A nonhalophilethat can grows best with almost no salt but can still
grow with low levels of salt (~ 7%) is called halotolerant.
In general, fungi are more tolerant of low water activity.
(That’s why your jelly is more likely to get contaminated by
fungi than bacteria.)

18. Nutritional Requirements
Growth of prokaryotes depends on nutritional
factors as well as physical environment
Main factors to be considered are:
Required elements
Growth factors
Energy sources
Nutritional diversity

19. Nutritional Requirements
Major elements (CHONPS + K, Mg, Fe, Ca)
Carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus,
potassium, magnesium, iron, and calcium
Essential components for macromolecules
Organisms classified based on carbon usage
Heterotrophs
Use organism carbon as nutrient source
Autotrophs
Use inorganic carbon (CO
2) as carbon source
Trace elements (Co, Cu, Ni, Zn, Se, Mg, Wo)
Cobalt, zinc, copper, molybdenum and manganese
Required in minute amounts
Assist in enzyme function
Nutritional diversity
Different organisms require the same nutrients but may require
different forms of the nutrients

20. Major elements

21. Element % dry wgtSource
Carbon 50 organic compounds or CO
2
Oxygen 20 H
2
O, organic compounds, CO
2
, and O
2
Nitrogen 14 NH
3
, NO
3
, organic compounds, N
2
Hydrogen 8 H
2
O, organic compounds, H
2
Phosphorus 3 inorganic phosphates (PO
4
)
Sulfur 1 SO
4
, H
2
S, S
o
, organic sulfur compounds
Potassium 1 Potassium salts
Magnesium 0.5 Magnesium salts
Calcium 0.5 Calcium salts
Iron 0.2 Iron salts

22. Carbon Source
Organic molecules
Heterotrophs
Inorganic carbon (CO
2)
Autotrophs

23. Nitrogen Source
Organic nitrogen
Primarily from the catabolism of amino acids
Oxidized forms of inorganic nitrogen
Nitrate (NO
3
2-
) and nitrite (NO
2
-
)
Reduced inorganic nitrogen
Ammonium (NH
4
+
)
Dissolved nitrogen gas (N
2
) (Nitrogen
fixation)

24. Phosphate Source
Organic phosphate
Inorganic phosphate (H
2PO
4
-
and HPO
4
2-
)

25. Sulfur Source
Organic sulfur
Oxidized inorganic sulfur
Sulfate (SO
4
2-
)
Reduced inorganic sulfur
Sulfide (S
2-
or H
2S)
Elemental sulfur (S
o)

26. Growth Factors
Some bacteria cannot synthesize some cell
constituents
These must be added to growth environment
Referred to as growth factors
Organisms can display wide variety of factor
requirements
Some need very few while others require many
These termed fastidious
Typical molecules
Amino acids
Nucleotide bases
Enzymatic cofactors or “vitamins”

27. Culture Media
4-27
Complex (contains undefined components)
Chemically defined (all concentrations are known)
Selective (favors the growth of a particular organism or
group of organisms)
Differential (has reactions that give isolates different
appearance)
Anaerobic (oxygen-free)

28. 4-28

29. Characteristics of Media