Bacterial growth is an orderly increase in the quantity of cellular constituents (i.e cell mass) and number. It depends upon the ability of the cell to form new protoplasm from nutrients available in the environment. When a bacterial cell is inoculated into a flask containing fresh culture medium and incubated, it enters into a rapid growth phase during which the bacterial cell divides and increases its population in the flask medium. Nutrients are substances used in biosynthesis and energy production and therefore are required for bacterial growth. All bacteria require several micro and macro nutrients.

1. BACTERIAL GROWTH &
NUTRITION
Meghna Banerjee
M.Sc Medical Microbiology
Medical College, Kolkata

2. SURVIVAL OF MICROORGANISMS IN THE NATURAL ENVIRONMENT
Population of microbes remains roughly constant.
This is because:
 Growth of microorganisms is balanced by death of
these organisms.
 Survival is influenced by successful competition of
nutrients.

3. The term “GROWTH”
Growth : orderly increase in the
sum of all the components of an
organism.
Cell multiplication is a consequence
of cell division of unicellular
organisms.
Growth leads to an increase in the

5. MEASUREMENT OF
MICROBIAL
CONCENTRATIONS
CELL CONCENTRATION
• The viable cell count is
typically considered the
measure of cell
concentration. For most
purposes, the turbidity of a
culture, measured by
photoelectric means, is
related to the viable count in
the form of a standard curve .
BIOMASS DENSITY
• In principle, biomass can be
measured directly by
determining the dry weight
of a microbial culture after it
has been washed with
distilled water.
• A standard curve is prepared
that correlates dry weight
with turbidity.

6. BACTERIAL
GROWTH
1.When Microorganisms are inoculatedin liquidmedium, they
usually are grown in batch culture.
2. BATCHCULTURE: Microorganisms are incubatedin a closed
culture vessel with a single batch of medium.
3. No fresh medium is providedduring incubation:
 Nutrient concentration decreases
&
 Concentration of waste increases.

7. BACTERIAL
GROWTH
CURVE
The growth of
population of microbes
reproducing by binary
fission in a batch culture
can be plotted as the
logarithm of the number
of viable cells versus the
incubation time.
Resulting Curve has
FOUR distinct phases.
LAG
LOG/
EXPONENTIAL
STATIONARY
DEATH

9. LAG PHASE
• No immediate increase in cell number
occurs.
• Cells are synthesizing new components.
• LAG PHASE can occur for a variety of
reasons:
a) Cells may be old & depleted of ATP,
essential cofactors & ribosome.
b) Medium may be different from the one
the microbes was growing in previously.

10. LOG/ EXPONENTIAL
PHASE
 Microorganisms are growing & dividing
at the maximal rate possible.
 Rate of growth is constant during the
exponential phase.
 They are completing the cell cycle &
doubling in number at regular intervals.

11. ……Log phase (continued)
 uniform population: in terms of
chemical & physiological properties.
 Exponential phase cultures are
used in biochemical & physiological
studies.
 Exponential growth is balanced: all
cellular constituents are
manufactured at constant rate
relative to each other.

12. STATIONARY PHASE
Population growth eventually
ceases & growth curve becomes
horizontal.
 Cell division stops due to depletion
of nutrients & accumulation of toxic
products.
 No. of progeny cells is just enough
to replace the number of cells that

13. ……Stationary phase (continued)
 Entry into stationary
phase in response to
starvation probably often
occurs in nature.
 Some Microbes have
evolved a no. of

14. STARVATION SURVIVAL STRATEGIES
 The action of protein RpoS is
central to starvation survival
strategies.
 RpoS : component of RNA Pol
holoenzyme- binds DNA &
initiates RNA synthesis.
 Directs other enzyme subunits
to the appropriate locations so
that transcription can begin.
 Directs the core enzyme to

15.  Starvation Proteins are made.
 They make cell much more resistant to damage by
starvation.
Increase peptidoglycan cross linking & cell wall
strength.
Dps Proteins protects DNA.
Chaperone proteins prevent protein denaturation&
renature damaged proteins.

16. PHASE OF DECLINE
 Population decreases due to cell
death.
 Cell death may be due to autolytic
enzymes.
 With autolytic bacteria, total count
shows a phase of decline.

17. Viable but non culturable (VBNC)
 Result of genetic response
triggered in starving stationary phase
cells.
 Able to become dormant without
changes in morphology.
 On availability of appropriate
conditions, VBNC microbes resume
growth.

18. PROGRAMMED CELL
DEATH
 A fraction of microbial population
is genetically programmed to die
after growth ceases.
 Cells die and the nutrients they
leak enable the eventual growth of
those that did not initiate cell death.

19. Mathematics of Growth
 During Exponential phase, each
microoragnism is dividing at constant
intervals.
 Thus the population doubles in
number during a specific length of
time: GENERATION (Doubling) TIME.
Mean growth rate: No. of
generations per unit time.

20. Measurement of Microbial
Growth
Direct
Measuremen
t of Cell
Numbers.
Viable
Counting
Methods.
Measuremen
t of Cell
Mass

21. Petroff-
Hausser
counting
chamber
• Direct Counts By using counting chambers.
MFT
• Membrane Filter Technique and the
subsequent use of fluorescent stains.
Flow
cytometry
• Flow Cytometry: creates a stream of cells
that passes through a beam of laser light.

22. 22
Microscopic counts
• Need a microscope, special slides, high power
objective lens
• Typically only counting total microbe numbers, but
differential counts can also be done

23. 23
Viable counts
• Each colony on plate or filter arises from single live cell
• Only counting live cells

24. 24
Direct Count
Pour Plate

25. 25

26. 26
Direct Count
Spread or
Streak Plate

27. 27

28. 28
Turbidity
• Cells act like large particles
that scatter visible light
• A spectrophotometer sends a
beam of visible light through
a culture and measures how
much light is scattered
• Scales read in either
absorbance or %
transmission
• Measures both live and dead
cells

29. CONTINUOUS CULTURE SYSTEM
Cells can be maintained in the exponential
phase by transferring them repeatedly
into fresh medium of identical
composition while they are still growing
exponentially.
This is referred to as continuous culture;
the most common type of continuous
culture device used is a chemostat.
Continuous culture is more similar to
conditions that organisms encountering

30. CHEMOSTATS
 Device consisting of a culture vessel equipped
with an overflow
siphon and a mechanism for dripping in fresh
medium
from a reservoir at a regulated rate.
 The medium in the culture
vessel is stirred by a stream of sterile air; each
drop of
fresh medium that enters causes a drop of culture
to siphon out.

31.  The vessel is inoculated, and the cells grow
until
the limiting nutrient is exhausted; fresh medium
from the
reservoir is then allowed to flow in at such a rate
that the cells use up the limiting nutrient as fast
as it is supplied.
 Under these conditions, the cell
concentration remains constant.
 The growth rate is directly proportionate to
the flow rate

32. The Chemostat

33. Chemostat Dilution Rate & Microbial Growth

34. TURBIDOSTATS
• Consists of photocell measuring
the turbidity of culture.
• Dilution rate varies unlike that in
the chemostat.
• All nutrients are in excess.
• Operates best at high dilution
rates whereas chemostat works
effectively at low dilution rates.

35. Bacterial
Nutrition…!!!

36. FACTORS THAT AFFECT
GROWTH
 Water
Carbon
 Nitrogen & Sulfur
Phosphorus
 trace elements

38. WATER:
• Vehicle for entry of nutrients.
•Elimination of all toxic products.
• Participates in metabolic reactions.
• Gives osmotic stability.
MACROELEMENTS
Carbon, Oxygen, Hydrogen, nitrogen, sulfur,
phosphorus are found in organic molecules
such as proteins, lipids, nucleic acids and
carbohydrates.

39. POTASSIUM:
Required for activity of a no. of
enzymes.
CALCIUM:
Confers heat resistance of bacterial
endospores.
MAGNESIUM:
Serves as cofactor, complexes with
ATP, stabilises ribosomes & cell
membranes.
Iron:
Involved in synthesis of ATP.

42. Microbial Response to Environmental
Factors
• Barophile
• Growth more rapid at high
hydrostatic pressure
Pressure
• small amounts of CO2 required for
growth.
• Capnophilic bacteria require
higher levels of CO2. (5-10%)
• e.g: Brucella abortus
Carbon
dioxide
• Bacteria grow well in the dark.
• Photochromogenic mycobacteria
form a pigment only on exposure to
light..
Light

43. Obligate
Aerobe
Facultative
Anaerobe
Aerotolerant
Anaerobe
Obligate
anaerobe
Microaerophile
Oxygen Concentration

45. TEMPERATURE & MICROBIAL
GROWTH
Psychrop
hile
Psychrotr
oph
Mesophil
e
Thermop
hile
Hyper-
thermophi
le

46. Mesophiles ( 20 – 45C)
Midrange temperature optima
Found in warm-blooded animals and in terrestrial and
aquatic environments in temperate and tropical latitudes
Psychrophiles ( 0-20C)
Cold temperature optima
Most extreme representatives inhabit permanently cold
environments
Thermophiles ( 50- 80C)
Growth temperature optima between 45ºC and 80ºC
Hyperthermophiles
Optima greater than 80°C
These organisms inhabit hot environments including boiling
hot springs, as well as undersea hydrothermal vents that
can have temperatures in excess of 100ºC

49. • Able to grow over a wide
range of water activity or
osmotic concentration.
• e.g: Saccharomyces rouxii
Osmotolerant
• Requires high levels of
NaCl, usually above 0.2
M, to grow.
• e.g: Halobacterium
Halophil
e
Solute & water
activity

50. Acidop
hile
• Growth
optimum
between pH
0 and 5.5.
• e.g:
Sulfobolus
Neutroph
ile
• Growth
optimum
between pH
5.5 and 8.0
• e.g:
Escherichia
Alkalop
hile
• Growth
optimum
between 8.0
and 11.5
• e.g:
Bacillus
alcalophilus
pH & Microbial Growth