This document discusses bacterial growth and summarizes key points about the growth cycle of bacteria. It notes that bacterial growth involves an increase in all chemical constituents and occurs through cell multiplication via binary fission. The growth cycle consists of four phases - lag phase, exponential/log phase, stationary phase, and death phase. The log phase is when bacteria multiply at their maximum rate and the time for one division is called the generation time. Population growth increases geometrically with each generation. Quantitative measurement of growth can occur through direct cell counting, measuring cell mass, or assessing cell activity.

1. Bacterial growth
By:
Mrs. Mali Dhanashri R.
Assistant professor,
GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical
Education and Reseach

2. Bacterial Growth
 Growth of Bacteria is the orderly increase of all the chemical
constituents of the bacteria.
 Multiplication is the consequence of growth.
 Death of bacteria is the irreversible loss of ability to reproduce.
 The process of DNA replication proceeds at a fixed rate & it’s
depend on temperature.
 Therefore the time taken to copy of an entire chromosome
depend on the number of base pairs within it & the growth
temperature.
 e.g Escherichia coil growing at 370C will take 45 mints for
replication of chromosome.

3. Generation /doubling time
 Generation time (g) : The time it takes the cells
to double.
 The average generative time is about 20-30
minutes in majority of medically important
bacteria.
 They are some exceptions among pathogenic
bacteria.
 Mycobacterium tuberculosis - 18 hrs.
 Mycobacterium leprae -10-20 days

4.  Length of generative time is in direct
dependence on the length of incubation
period of infections.
 In DNA replication, chromosome segregation
(C-phase) & cell divison (D-phase) occur
sequentially in slow-growing cells with
generation times of greater than 1 hr & are
the final events of the bacterial cell.
 Cells are able to replicate faster than once
every hour by initiating several rounds of
DNA replication at a time.

5. Population growth
 Population growth means an orderly
increase in all cellular constituents.
 Increase of mass may not really reflects
growth because there is only increase in the
size & weight of the cell.
 All actively growing cells mainly multiply by
the binary fission.
 In the binary fission one specific cell
undergoes division to give rise to the
formation of two cells.

6.  Thus, population growth increases, geometrically..
1 2 22 23 24 …. 2n
Where, n = number of generations.
 Assuming that there is no cell death at all, each
succeding generation shall give rise to double its
population.
 Thus, the total population N at the end of a specific
given time period is expressed as….
N = 1 x 2n
 But, under practical condition, it is difficult to
inoculate only one bacteria so formula as..
N = N0 x 2n
 No is the number of bacteria inoculated at time zero.

7.  Taking logarithm on both sides…
log N = log No + n log 2
n = log N – log No
log 2
n = log N – log No/ 0.301
n = 3.3 (log N – log No )
 If we know the initial population & the
population after growth then we can calculate
the number of generation by using the above
formula.
 The actual generation time is calculated by
dividing n into t where t represents the hours
or minutes of exponential growth.

8. Growth Kinetics/ Growth
Curve
 Growth curve of the bacteria obtained by inoculating a small
number of bacterial cells into a suitable culture medium &
counting the bacterial samples at regular intervals.
 When logarithms of the number of bacteria vs times on graph
paper the specific curve found that resulting curve is called
bacterial curve.
 The resulting curve has four distinct phases…
1. Lag phase
2. Log or logarithmic or exponential phase
3. Stationary phase
4. Death or decline phase

10. 1. Lag phase
 Lag phase is the phase or period between
inoculation & the starting the multiplication of
bacteria.
 Immediately following the seeding of a
culture medium.
 A period of adaptation for the cells to their
new environment
 cells are adapting to the high-nutrient
environment and preparing for fast growth.

11.  The lag phase has high biosynthesis rates.
 In that phase bacterial cell are synthesised
the enzymes, coenzymes & other essential
molecules and built up in adequate
quantities for rapid growth & multiplication
to proceed.
 In that phase cells are metabolically &
physiologically very active but do not
divide.
 The length of the lag phase depend upon
nature of medium, species of
microorganism & other factors.

12.  A slight increase in cell mass and volume,
but no increase in cell number.
 Duration of the lag phase varies with
 the species
 size of inoculum - Prolonged by low
inoculum volume, poor inoculum
condition (high % of dead cells)
 age of inoculum
 Nature of the culture medium (Prolonged
by nutrientpoor medium)
 And environmental factors like
temperature, pH etc

13. 2. Log/Exponential growth
phase
 In this phase, the cells have adjusted to their new
 environment and multiply rapidly (exponentially)
 • The bacteria will grow and divide at a doubling time
 characteristic of the strains and determined by the
 conditions during the exponential phase.
 • During this phase, the number of bacteria will
increase to
 2n, in which n is the no.of generations.
 • Balanced growth –all components of a cell grow at
the
 same rate.

14.  In that phase bacteria cells rapidly grow.
 Means in that phase bacteria multiply at their
maximum rate & their number increases
exponentially.
 The time required for one bacterial division during
this phase is known as generation time.
 The number of bacteria present in each generation
period is almost twice that in previous period.
 At this phase the log of number of cells plotted
against time result in a straight line.
 The generation time (g) can be determined from the
number of generations (n) that occurs in particular
time (t)
 g = t/n
 t/n = t / 3.3 (log N – log N0 )

15. Deceleration growth phase
 Very short phase, during which growth
decelerates due to either:
 Depletion of one or more essential
nutrients
 The accumulation of toxic by-products of
growth
 (e.g. Ethanol in yeast fermentations)
 Period of unbalanced growth: Cells
undergo internal restructuring to increase
their chances of survival

16. 3.Stationary phase:
 In stationary phase cells is maintained a balance
between cell division & cell death.
 In that phase multiplication is reduced because
depletion of nutrition, accumulation of toxic waste
products, very high conc. of cells & low partial
pressure of oxygen.
 The bacteria stop growing and enter the
stationary phase.
 At this phase cells consumed reserve food
materials, proportion of ribosomes may be
degraded & enzymes may still be synthesized.

17.  The growth rate equals the death rate – The
number of progeny cells formed is just
enough to replace the number of cells that
die.
 At this phase the log of number of cells
plotted against time result in a no change
in line.
 There is no net growth in the organism
population – The viable count remains
stationary as an equilibrium exists between
the dying cells and newly formed cells.

18. 4. Death Phase
 Phase of decline
 In that phase, the number of bacterial cells
decreases exponentially, essentially the
inverse of growth during the log phase.
 A variety of conditions involved to
bacterial death but mostly responsible are
depletion of nutrition & accumulation of
toxic waste products etc.
 At this phase the log of number of cells
plotted against time result in decline the
line.
 Cell death may also be caused by autolytic
enzymes.

19. Generation times
Sr.
No.
Bacterium Medium Generation
Time
(minutes)
1. Escherichia coli Glucose-salts 17
2. Bacillus megaterium Sucrose-salts 25
3. Streptococcus lactis Milk 26
4. Streptococcus lactis Lactose broth 48
5. Mycobacterium
tuberculosis
Synthetic 792-932
6. Staphylococcus aureus Heart infusion
broth
27-30
7. Lactobacillus
acidophilus
Milk 66-87

20. Growth & Genetic exchange
 For many years it was thought that bacteria, unable to
exchange genetic material and could only adapt and
evolve through mutation of genes.
 The bacteria has profound ability to exchange and share
DNA across diverse genera.
 This is of particular significance because it enables
bacterial populations to adapt rapidly to changes in their
environment,.
 This also help in the deployment of antibacterial
chemicals and antibiotics.
 Three major process involved in genetic exchange….
 Transformation
 Transduction
 Conjugation

21. Transformation
 Discovered by Frederick Griffith in 1928.
 The early work on the transfer of virulence in the
pathogen Streptococcus pneumoniae .
 The stage for the research that first showed that
DNA was the genetic material.
 Griffith found that if he boiled virulent bacteria and
injected them into mice, the mice were not affected
and no pneumococci could be recovered from the
animals.
 When he injected a combination of killed virulent
bacteria and a living nonvirulent strain, the mice
died; moreover, he could recover living virulent
bacteria from the dead mice.
 Griffith called this change of nonvirulent bacteria
into virulent pathogens transformation.

23.  Many bacteria can acquire new
genes by taking up DNA molecules
(ex: plasmid) from their
surroundings.
 When bacteria undergo lysis, they
release considerable amounts of
DNA into the environment.
 This DNA may be picked up by a
competent cell- one capable of
taking up the DNA and undergoing
a transformation.
 To be competent, bacteria must
be in the logarithmic stage of
growth, and a competence
factor needed for the
transformation must be present.

24. Transduction
 It is defined as a phenomenon causes
genetic recombination in bacteria wherein
DNA is carried from one specific bacterium
to another by a bacteriophage.
 Bacterial viruses ( bacteriophages)
transfer DNA fragments from one bacterium
(the donor) to another bacterium (the
recipient).
 The viruses involved contain a strand of
DNA enclosed in an outer coat of protein.

26.  After a bacteriophage enters a bacterium, it
may encourage the bacterium to make copies of
the phage.
 At the conclusion of the process, the host
bacterium undergoes lysis and releases new
phages. This cycle is called the lytic cycle.
 Under other circumstances, the virus may
attach to the bacterial chromosome and
integrate its DNA into the bacterial DNA.
 It may remain here for a period of time before
detaching and continuing its replicative
process. This cycle is known as the lysogenic
cycle.

27.  Under these conditions, the virus does not
destroy the host bacterium, but remains in a
lysogenic condition with it. The virus is called a
temperate phage, also known as a prophage.
 At a later time, the virus can detach, and the
lytic cycle will ensue.
 It will express not only its genes, but also the
genes acquired from the donor bacterium.
 As well as temperate phage will be active once
again at a low frequency & phasing between
temperate & lytic forms ensures the long-term
survival of the virus.

29. Conjugation
 Conjugation is a natural process
representing the early stages in a true
sexually reproductive process.
 In that transcribed to produce singular
viral elements, which cannot assemble
or lyse the host cell. Such DNA strand
are known as plasmids.
 Plasmids are circular & can either be
integrated into the main chromosome,
in which case they are replicated along
with chromosome & passed to daughter
cells or they are separate from it & can
replicate independently.
 The simplest form of plasmid is F-factor
(fertility factor).
 The cells containing an F-factor are
designed F+

30.  The F-pilus is a hollow appendage that is capable of
transferring DNA from one cell to another.
 In its simplest form an unassociated F-factor will
simply transfer a copy to a recipient cell & such a
transfer process is known as cojugation.
 Two bacterial cells come together and mate such that
a gene transfer occurs between them.
 Can only occur between cells of opposite mating types.
 – The donor (or "male") carries a fertility factor (F+).
 – The recipient ("female") does not (F−).
 One cell, the donor cell (F+), gives up DNA; and
another cell, the recipient cell (F−), receives the DNA.

31.  • The transfer is nonreciprocal,
and a special pilus called the
sex pilus joins the donor and
recipient during the transfer.
 The channel for transfer is
usually a special conjugation
tube formed during contact
between the two cells.
 The DNA most often transferred
is a copy of the F factor
plasmid.
 The factor moves to the
recipient, and when it enters
the recipient, it is copied to
produce a double-stranded DNA
for integration.

32. Synchronous growth
 A synochronous or synochronized culture is a microbial
culture or cell culture that are all in the same growth
stage.
 Thus, the entire population is kept uniform with respect
to growth & division.
 But practically it is not possible to determine a single
bacterial cell to obtain the information about growth
behavior.
 Synchronous culture provides the entire cell crop in the
same stage.
 Synchronized culture provides information on
measurement made on such culture are equivalent to the
measurement made on individual cells.

33.  A synchronous population can be generated
either by physical separating cells in the
same stage of division or by forcing a cell
population an identical, physiological
condition by change in the environment.
 physical separation done by centrifugation,
filtration or by periodic changes in
nutritional & environmental conditions
produce synchronously dividing cell
populations.
 The synchrony is generally lost after a few
generation.

35. Continuous growth
 In that technique microbial population is maintained
in the log phase or exponential phase of growth in a
constant environment.
 It is necessary maintained population for research &
industrial process.
 This technique or condition also known as steady
state growth.
 In this apparatus fresh medium flows into growth
chamber at a controlled rate.
 The rate of growth is then controlled by regulating
the inflow rates. Hence in a chemo stat apparatus,
indefinite growth at any constant are can be
maintained.

37. QUANTITATIVE MEASUREMENT
OF BACTERIAL GROWTH
 The term growth as commonly applied in microbiology
refers to the magnitude of the total population.
 Growth in this sense can be determined by numerous
techniques based on one or more of the following types
of measurement:
1. Cell count: Directly by microscopy or by using an
electronic particle counter, or indirectly by a colony count
2. Cell mass: Directly by weighing or by a measurement of
cell nitrogen, or indirectly by turbidity
3. Cell activity: Indirectly by relating the degree of
biochemical activity to the size of the population

38. Direct Microscopic count:
 Bacteria can be counted easily and accurately
 Use Petroff-Hausser counting chamber
 A suspension of unstained bacteria added in the chamber.
 Counting bacteria with help of a phase-contrast
microscope.
 It is rapid and simple method.
 The morphology of the bacteria can be observed as they
are counted.
 Very dense suspensions can be counted by diluting
appropriately.
 Disadv: Suspensions having low numbers of bacteria, e.g.,
at the beginning of a growth curve, cannot be counted
accurately.

39.  This is a special slide accurately ruled into squares that
are 1/400 mm2 in area; a glass cover slip rests 1/50 mm.
above the slide, so that the volume over -a square is
1/20,000 mm 3 (1/20,000.000 cm3).
 If, for example, an average of five bacteria is present in
each rifled square, there are 5 x 20,000;000, or 108,
bacteria per milliliter.

40. Electronic Enumeration of
Cell Numbers
 In this method, the bacterial suspension is placed inside
an electronic particle counter.
 The bacteria are passed through a tiny orifice 10 to 30
gm in diameter.
 As each bacterium passes through the orifice, the
electrical resistance between the two ompartments
increases momentarily.
 This generates an electrical signal which is automatically
counted.
 This method is rapid.
 But requires sophisticated electronic equipment;
moreover, the orifice tends to become clogged.

41.  The main disadvantage of direct counting of cell numbers is that
there is no way to determine whether the cells being counted
are viable.
 To determine the viable count of a culture, we must use a
technique that allows viable cells to multiply, such as the plate-
count method or the membrane-filter method.

42. The Plate-Count Method
 This method allows determination of the number of cells that
will multiply under certain defined conditions.
 A measured amount of the bacterial suspension is introduced
into a Petri dish, after which the agar medium (maintained in
liquid form at 45°C) is added and the two thoroughly mixed by
rotating the plate. When the medium solidifies, the organisms
are trapped in the gel.
 Each organism grows, reproducing itself until a visible mass of
organisms—a colony—develops; i.e., one organism gives rise to
one colony.
 Hence, a colony count performed on the plate reveals the
viable microbial population of the inoculum.

43.  Limitation: Only bacteria that will be counted are those
which can grow on the medium used and under the
conditions of incubation provided.
 Difficult to count a mixture of bacteria.
 Another, each viable organism that is capable of growing
under the culture conditions provided may not necessarily
give rise to one colony.
 The development of one colony from one cell can occur
when the bacterial suspension is homogeneous and no
aggregates of cells are present.
 The cells have a tendency to aggregate, e.g., cocci in
clusters (staphylococci), chains (streptococci), or pairs
(diplococci), the resulting counts will be lower than the
number of individual cells.
 For this reason the counts" are often reported as colony-
forming units per milliliter rather than number of bacteria
per milliliter.

44.  The original sample is usually diluted so that the number
of colonies developing on the plate will fall in the range of
30 to 300.
 Within this range the count can be accurate, and the
possibility of interference of the growth of one organism
with that of another-is minimized.
 Colonies are usually counted by illuminating them from
below (dark-field illumination) so that they are easily
visible, and a large magnifying lens is often used .
 Various electronic techniques
have been developed for
the counting of colonies.
Colony Counter

45.  The plate-count technique is used routinely and with
satisfactory results.
 Used for the estimation of bacterial populations in milk,
water, foods, and many other materials.
 It is easy to perform and cart be adapted to the
measurement of populations of any magpitude.
 Advantage: sensitivity, since very small numbers of
organisms can be counted.
 Theoretically, if a specimen contains as few as one
bacterium per milliliter, one colony should develop upon
the plating of 1 ml.

47. Membrane-Filter Count
 A very useful variation on the plate-count technique is
based on the use of molecular or membrane filters.
 These filters have a known uniform porosity of
predetermined size sufficiently small to trap
microorganisms. T
 his technique is particularly valuable in determining the
number of bacteria in a large sample that has a very small
number of viable cells.
 e.g., the bacteria in a large volume of air or water can be
collected simply by filtering them through an assembly.

49. Turbidimetric Methods
 bacteria in a suspension absorb and scatter the light passing
through them.
 A culture of more than 107 to 108 cells per milliliter appears
turbid to the naked eye.
 A spectrophotometer or colorimeter can be used for
turbidimetric measurements of cell mass.
 It is a simple, rapid method for following growth.
 The culture to be measured must be dense enough to register
some turbidity on the instrument.
 Disadv: It may not be possible to measure cultures grown in
deeply colored media or cultures that contain suspended
material other than bacteria.
 It must also be recognized that dead as well as living cells
contribute to turbidity.

50. Determination of Nitrogen
Content
 The major constituent of cell material is protein.
 Since nitrogen is a characteristic part of proteins, one can measure a
bacterial population or cell crop in terms of bacterial nitrogen.
 Bacteria has average approximately 14 percent nitrogen on a dry-weight
basis.
 This may subject to some variation introduced by changes in cultural
conditions or differences between species.
 First harvest the cells and wash them free of medium.
 Then perform a quantitative chemical analysis for nitrogen.
 It is somewhat laborious and can be performed only on specimens free of all
other sources of nitrogen.
 Furthermore, the method is applicable only for concentrated populations.
For these and other reasons, this procedure is used primarily in research.

51. Determination of the Dry Weight
of Cell
 This is the most direct approach for quantitative measurement of
a mass of cells.
 It can be used only with very dense suspensions, and the cells
must be washed free of all extraneous matter.
 Dry weight may not always be indicative of the amount of living
material in cells.
 E.g. In the Azotobacter, the intracellular reserve material poly-6-
hydroxybutyrate can accumulate at the end or the log phase of
growth and during the stationary phase and finally can comprise
up to 74 percent of the dry weight of the cells.
 Thus, the dry weight may continue to increase without
corresponding cell growth.
 Yet, for many organisms the determination of dry weight is an
accurate and reliable way to measure growth and is widely used in
research.

52. Measurement of a Specific
Chemical Change
 Bacterial population is count on basis of specific
chemical change Produced on a Constituent of the
Medium.
 As an example of this method of estimating cell mass,
we may take a species that produces an organic acid
from glucose fermentation.
 The assumption is that the amount of acid produced,
under specified conditions and during a fixed period of
time, is proportional to the magnitude of the bacterial
population.
 Admittedly, the measurement of acid or any other end
product is a very indirect approach to the
measurement of growth and is applicable only in
special circumstances.

53. Methods for Measuring Bacterial Growth
Sr.
No.
Method Some Applications Growth
Expression
1.
Microscopic count Enumeration of bacteria in
vaccines and cultures
Number of cells
per ml
2.
Electronic
enumeration
Same as for microscopic
count
Number of cells
per ml
3.
Plate count Enumeration of bacteria in
milk, water, foods, soil,
cultures, etc.
Colony-forming
units per ml
4.
Membrane filter Same as plate count Colony-forming
units per ml
5.
Turbidimetjic
measurement
Microbiological assay,
estimation of cell crop in
broth, cultures, or aqueous
suspensions
Optical density
(absorbance)

54. Sr. No. Method Some Applications Growth
Expression
6.
Nitrogen
determination
Measurement of cell
crop from heavy
culture suspensions to
be used for research
in metabolism
Mg nitrogen per
ml
7.
Dry weight
determination
Same as for nitrogen
determination
Mg dry weight of
cells per ml
8.
Measurements of
biochemical
activity, e.g., acid
production by
cultures
Microbiological assays Mllliequlvalents
of acid per ml or
per culture

55. Factors Required for
Bacterial Growth
 The requirements for bacterial growth are:
(A) Environmental factors
(B) Sources of metabolic energy.
 Bacteria required the nutrition's, pH, oxygen &
temperature for growth & multiplication process.
 So, for cultivation of microorganism required
elements such as sodium, potassium, magnesium
& iron.
 As well as in media required contains of source of
carbon, nitrogen, hydrogen, oxygen & phosphorus.

56. Nutrients
 Nutrients in growth media must contain all
the elements necessary for the synthesis of
new organisms.
 Hydrogen donors and acceptors
 Carbon source
 Nitrogen source
 Minerals : sulphur and phosphorus
 Growth factors: amino acids, purines,
pyrimidines; vitamins
 Trace elements: Mg, Fe, Mn.

58. Source of energy:
 Bacteria may obtain energy from sunlighyt
or chemicals.
 Phototrophs bacteria :
 Energy obtained from sunlight .
 e.g. Rhodospirillum rubrum.
 chemotrophs bacteria :
 Energy obtained from chemical reaction.
 e.g. Escherichia coli or E-coli.

59. Source of electrons:
 All bacteria required electrons for metabolism.
1. Lithotrops :
 In that type of bacteria species use the inorganic
compounds as electron donor
 e.g pseudomonas pseudoflava.
2. Organotrophs :
 In that type of bacteria species use the organic
compounds as electron donor
 e.g Escherichia coli or E-coli.
3. Photolithotrophs :
 some phototropic bacteria use inorganic compound
(H2S) as source of electron.
 e.g. Chromatium okenii.

60. 4. Photoorganotrophs:
 some phototropic bacteria use organic compound such
as fatty acids & alcohols as electron donors
 e.g Rhodospirillum rubrum.
5. Chemolithotrophs:
 Some chemotrophic bacteria use inorganic compound as
source of electron.
 e.g. Nitrosomonas europaea.
6. Chemoorganotrophs:
 Some chemotrophic bacteria use organic compound such
as sugar &amino acids as electron donors
 e.g Escherichia coli or E-coli.

61. Source of carbon:
 Microorganism required carbon for synthesizing cell
components.
 Autotrophs:
 some species use CO2 as the major source of carbon
these microorganisms are called autotrophs.
 e.g. Chromatium okenii.
 Heterotrops:
 some species use organic compounds as a source of
carbon such species are called heterotrophs.
 e.g. Escherichia coli or E-coli.

62. Other Nutrients:
 Nitrogen:
 Nitrogen is the major component of protein & nucleic
acids, so that bacteria can use nitrogen from the
atmosphere or from inorganic compounds such as
nitrites, nitrate.
 Sulphur:
 Sulphur is needed for synthesis of amino acids.
 Phosphorus:
 Phosphorus usually supplied in the form of phosphate is
an essential component of nucleotides, nucleic acid
etc.

63.  Water:
 It is the major essential nutrient as it account for
about 80 to 90% of the total weight of cell.
 Mineral salts:
 Bacteria require salts, particularly the anions such
as phosphate & sulphate & the cations as sodium,
potassium, magnesium, iron & calcium.
 These are present in the natural environment or may
be added in cultural media.

64. Temperature
 Microorganisms are sensitive to temperature changes
 Usually unicellular
 Enzymes have temperature optima
 If temperature is too high, proteins denature, including
enzymes, carriers and structural components
 Temperature ranges are enormous (-20 to 100oC)
 Organisms exhibit distinct cardinal temperatures (minimal,
maximal, and optimal growth temps)
 If an organism has a limited growth temperature range =
stenothermal (e.g. N. gonorrhoeae)
 If an organism has a wide growth temperature range =
eurythermal (E. faecalis)

65.  Based on temperature tolerance and its influence on
growth , bacteria may be classified as:
 Psychrophiles
 can grow well at 0oC, have optimal growth at 15oC or
lower, and usually will not grow above 20oC
 Arctic/Antarctic ocean
 Protein synthesis, enzymatic activity and transport
systems have evolved to function at low
temperatures
 Cell walls contain high levels of unsaturated fatty
acids (semi-fluid when cold)

66.  Psychrotrophs or facultative psychrophiles:
 Can also grow at 0oC,
 but have growth optima between 20oC and 30oC, and growth
maxima at about 35oC
 Many are responsible for food spoilage in refrigerators
 Mesophiles:
 have growth minima of 15 to 20oC, optima of 20 to 45oC, and
maxima of about 45oC or lower
 Majority of human patho
 Thermophiles:
 have growth minima around 45oC, and optima of 55 to 65oC
 Hot springs, hot water pipes, compost heaps
 Lipids in PM more saturated than mesophiles.
 Hyperthermophiles
 have growth minima around 55oC and optima of 80 to 110oC
 Sea floor, sulfur vents gens

67. Temperature
optima of
bacteria
Effect of
Temperature

68. pH
 pH is the negative logarithm of the hydrogen ion
concentration
 Each bacterium has definite pH range for growth and
multiplication.
 Depend on pH value microorganism are classified as:
 Acidophiles grow best between pH 0 and 5.5
 Neutrophiles grow best between pH 5.5 and 8.0
 Alkalophiles grow best between pH 8.5 and 11.5
 Extreme alkalophiles grow best at pH 10.0 or higher.
 Sudden pH changes can inactivate enzymes and damage
plasma membrane
 Reason for buffering culture medium, usually with a weak
acid/conjugate base pair (e.g. KH2PO4/K2HPO4 – monobasic
potassium/dibasic potassium)

69. pH profiles for some prokaryotes

70. Oxygen concentration
 Obligate aerobes are completely dependent on
atmospheric O2 for growth
 Oxygen is used as the terminal electron acceptor for
electron transport in aerobic respiration
 Facultative anaerobes do not require O2 for growth,
but do grow better in its presence
 Aerotolerant anaerobes ignore O2 and grow equally
well whether it is present or not.

71.  Obligate (strict) anaerobes do not tolerate O2 and die
in its presence.
 Microaerophiles are damaged by the normal
atmospheric level of O2 (20%) but require lower levels (2
to 10%) for growth

72. Oxygen and growth

73. Water availability
 Water is solvent for biomolecules, and its availability is
critical for cellular growth
 The availability of water depends upon its presence in
the atmosphere (relative humidity) or its presence in
solution or a substance (water activity, (Aw))
 Aw of pure water (100%) is 1.0; affected by dissolved
solutes such as salts or sugars.
 Microorganisms live over a range of aW from 1.0 to 0.7.
 The aW of human blood is 0.99; seawater = 0.98; maple
syrup = 0.90; Great Salt Lake = 0.75. Water activities in
agricultural soils range between 0.9 and 1.0.

74. Effect of salt on growth

75. Pressure
 Barotolerant organisms are adversely
affected by increased pressure, but not as
severely as are nontolerant organisms
 Barophilic organisms require, or grow more
rapidly in the presence of increased
pressure
Light:
 Optimum condition for growth is darkness.

76. Radiation
 Ultraviolet radiation damages cells by causing
the formation of thymine dimers in DNA.
 Ionizing radiation such as X rays or gamma
rays are even more harmful to
microorganisms than ultraviolet radiation
 Low levels produce mutations and may
indirectly result in death
 High levels are directly lethal by direct
damage to cellular macromolecules or
through the production of oxygen free
radicals.

77. (B) Sources of Metabolic
Energy
 Mainly three mechanisms generate
metabolic energy. These are
 Fermentation
 Respiration and
 Photosynthesis.
 An organism to grow, at least one of these
mechanisms must be used.

78. Bacterial Classification
 Bacteria are classified based on various
factors
 shape (morphology)
 Cell wall structure
 Respiration (metabolism)
 type of nutritional source
 characteristic
 environmental factor etc.

79. Bacterial Classification Based on Shapes
 Bacilli: Rod shaped bacteria.
 • Diplobacilli, tetrad , palisade (two cells arranged parallel) or
 sterptobacilli (chain arrangement). e.g. E.Coli and Salmonella
 Coccus: Spherical or oval cells shaped bacteria which is further
 classified as monococcus, diplococci, streptococci, Staphylcocci
 e.g. Staphylococcus and Streptococcus
 Spiral: Spiral shaped bacteria are called spirilla
 e.g. Treponema and Borellia
 sub divided into spirilla (rigid spiral forms) and
 spirochetes(flexible spiral forms).
 Comma shaped: Vibrio
 Branching filamentous forms : Actinomycetes

80. Bacterial Classification Based on
Staining Methods
 Gram positive bacteria :
 Take up crystal violet dye and retain their blue or violet
color.
 Gram negative bacteria :
 Do not take up crystal violet dye, and thus appear red or
pink.
Classification Based on
Respiration
 Aerobic Respiration :
 Sugars are broken down in the presence of oxygen to
produce carbon dioxide, water, and energy.
 Anaerobic Respiration :
 anaerobic respiration breaks down sugars and releases
energy in the absence of oxygen.

81. Classification Based on
Environment
 Mesophiles - which require moderate temp to survive.
 Neutrophiles - require moderate conditions to survive.
 Extremophiles - can survive in extreme conditions.
 Acidophiles - which can tolerate low pH conditions.
 Alkaliphiles - which can tolerate high pH conditions.
 Thermophiles - which can resist high temperature.
 Psychrophiles - can survive extremely cold conditions.
 Halophiles - can survive in highly saline conditions.
 Osmophiles - can survive in high sugar osmotic conditions.

82. Classification Based on Flagella
 Atrichous (no flagella),
 monotrichous (uni flagella)
 amphitrichous (bi flagella)
 polytrichous (more flagella)
Classification Based on Spore
Formation
 spore forming
 non-spore forming

83. Classification Based on their
association with host
 Beneficial
 Pathogenic
 Harmless
Classification Based on Capsule
 Capsulated
 Encapsulated

84. Nutritional Source
 Autotrophs:
 obtain the carbon it requires from carbon dioxide
 Photoautotrophs:
 Directly use sunlight in order to produce sugar from
carbon dioxide.
 Chemoautotrophs :
 Depend on various chemical reactions.
 use inorganic energy sources, such as hydrogen sulfide,
elemental sulfur, ferrous iron, molecular hydrogen, and
ammonia.

85. Nutritional Source
 Heterotrophs :
 Heterotrophic bacteria obtain sugar from
the environment they are in (ex: the living
cells or organisms they are in).
 symbiotic
 saprophytes
 parasite

86. Chemostat
 A continuous culture device that maintains a constant growth
rate by:
 supplying a medium containing a limited amount of an
essential nutrient at a fixed rate
 removing medium that contains microorganisms at the same
rate
 As fresh media is added to the chamber, bacteria are removed
 Limiting nutrients control growth rates
 Cell density depends on nutrient concentration
Turbidostat
 A continuous culture device that regulates the flow rate of
media through the vessel in order to maintain a predetermined
turbidity or cell density
 There is no limiting nutrient
 Absorbance is measured by a photocell (optical sensing device)