Here is presentation of how physical conditions like temperature PH and other factors affect bacterial growth. Culturing conditions for bacterial which factors are important for bacterial growth what we take in consideration for bacterial growth

1. Physical conditions required
for bacterial growth
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2. Cultivation of bacteria
•Nutritional requirements
•Nutritional types of bacteria
•Bacteriological Media
•Physical conditions required for growth
•Choice of media and incubation conditions

3. Why we cultivate bacteria
•A microbiological culture or microbes culture is
a method of multiplying microorganisms by
letting them reproduce in predetermined culture
medium under controlled laboratory conditions.
•It is also used to determine type of organisms.
•It is also use to determine abundance of
organisms in sample being tested.

4. Physical conditions
• Just as nutritional requirements bacteria physical conditions
physical conditions for growth of bacteria are also diverse.
• Bacteria show different responses to physical conditions such
as:-
• Temparature
• Gases
• PH
• Salt concentration and acidity of water

5. Temperature
•As rate of all the chemical reactions that are
important for growth of bacteria are really
influenced by temperature.
•Temparature at which bacterial growth increase
rapidly during short period of time is the
optimum growth temperature of that bacteria.

6. Optimum temperature
•Optimum temperature is actually range within
which bacteria will grow.
•It can be seen that maximum temperature at
which growth occur is usually quite close to
optimum temperature.
•While minimum temperature for growth is much
less than optimum temperature.

8. Groups of bacteria on basis of temperature
relationship
•Psychrophiles:-
•These bacteria are able to grow at 0 degree
temperature or lower.
•Though they grow best at higher temperature.
•Mostly microbiologist restrict this psychrophiles
term to organisms that can grow at 0 degree
celcius temperature but have optimum
temperature of 15 degree celcius

9. •Maximum temperature for psychrophiles is 20
degree celcius
•Facultative psychrophiles or psychrotrophs are
those that are able to grow at 0 degree celcius but
grow best at 20 or 30 degree celcius.

10. Isolation of strict psychrophiles
•It becomes necessary to maintain source sample at
cold temperature from the time they are collected
also to chill media before attempting isolation
•Maintaining cold temperature is necessary because
strict psychrophiles usually die if they are even
temporary exposed to room temperature.
•Even at optimum temperature these bacteria takes
two or three weeks for development.

11. Physiological factors for low temperature
maxima of strict psychrophiles
•Some factors that are responsible for low
temperature maxima of these bacteria are
•Heat instability of ribosomes
•Heat instability of enzymes
•Increased leakage of cell components
•Impared transport of nutrients above maximum
temperature

12. •Mesophiles:-
•These bacteria grow best within temperature
range of approximately 25 to 40 degree celcius.
•For example all bacteria that are pathogenic for
humans are mesophiles
•All warm blooded animals are mesophiles
•So these grow best at body temperature of 37
degree celcius.

13. •Thermophiles:-
•These bacteria grow best at temperature of about
45 degree celcius.
•Facultative thermophiles are those bacteria that
have growth range extended to mesophilic region
•Obligate thermophiles are those that can’t grow
in mesophilic region these are also known as true
or steno-thermophiles

14. Physiological factors responsible for ability of
these bacteria to grow at high temperature
•There are certain factors responsible for this
ability of bacteria these are as follows:-
•Increased thermal stability of ribosomes.
•Increased thermal stability of membrane and
certain enzymes.
•Loss of fluidity that exists within lipid bilayer of
cytoplasmic. membrane may be factor governing
minimum temperature.

15. Certain examples:-
•Seratia marcescens form blood red to orange
pigment when cultured at 25 degree celcius but
no pigment or produce little pigment when grow
at 37 degre celcius.
• Lactobacillus plantarum does not require amino
acid phenylalanine for growth when cultured at
25 degree celcius but require this amino acid
when cultured at 37 degree celcius.

16. Gaseous requirements
• The physical gases that affect bacterial growth are carbon
dioxide and oxygen.
• Bacteria are divided into four groups:-
• Aerobic bacteria require oxygen for growth and can grow
when incubated in air atmosphere.
• Anaerobic bacteria they can’t grow when incubated in air
atmosphere. Some can tolerate low levels of oxygen are
nonstringent or tolerant anaerobes but others that can’t
tolerate even low level of oxygen are stringent or strict
anaerobes.

17. •Facultative anaerobes bacteria do not require
oxygen for growth also they use oxygen for
energy production. They are not inhibited by
oxygen as well grow well in atmospheric oxygen
as they do in absence of oxygen.
•Microaerophilic bacteria require low levels of
oxygen for growth but can’t tolerate level of
oxygen present in air atmosphere.

18. Oxygen toxicity
• Oxygen is both beneficial and poisonous to living
organisms.
• Oxygen is beneficial because it has strong oxidizing
ability.
• It is excellent terminal electron for for energy yielding
process known as respiration.

19. • However oxygen is also a toxic substance.
• Aerobic and facultative organisms develop protective
mechanism that mitigate toxicity.
• Microaerophilic and anaerobic are deficient in these
mechanisms and restricted to habitat where little or no
oxygen.

20. Factors that implicate in oxygen toxicity
• Oxygen inactivates enzymes molecular oxygen can directly
oxidize essential reduced groups such as thiol(-SH) group or
enzyme results in in activation of enzymes.
• For example enzyme complex nitrigenase responsible for
nitrogen fixation is irreversibly destroyed by small amount of
oxygen
• Demage due to toxic derivatives of oxygen:- various enzymes
catalyze chemical reactions involves molecular oxygen these
reactions involve addition of single electron to oxygen
molecule to form super oxide.
• O2+e=o2

22. • Superoxide radicals can inactivate vital cell component they
further react to form hydrogen peroxide and hydroxyl radical.
• O2+2H>o2+H2O2
O2 + H2O2> O2 + OH-
• Hydroxyl radical amoung most reactive free radical and can
damage almost every kind of molecules found in living cells.
• Hydrogen peroxide is not free radical but it is a powerful
oxidizing agent that is highly toxic.

23. Protective mechanism for oxygen toxicity
• Aerobic and facultative organisms have developed protective
mechanism against toxic form of oxygen.
• One enzyme is known as super oxide dismutase which
eleminates superoxide radical by increasing rate of reaction.
• Hydrogen peroxide produced by this reaction can in turn be
dissipated by catalase and peroxide enzyme.
• H2o2 > 2H20 + O2

26. Cultivation of Aerobic Bacteria
• To grow aerobic and facultative bacteria in flasks or tubes
then incubate the medium under normal atmospheric
conditions.
• However when aerobic organisms are be grown in
atmosphere by dispensong media in shallow layers for which
special containers are available.
• Aeration can also be increased by shaking the inoculated
liquid culture.

27. Cultivation of anaerobic bacteria
• Stringent anaerobes can be grown only by taking special
precautions to exclude all atmospheric oxygen from medium.
• Such environment can be established by using following
methods:-
• Prereduced media
• Anaerobic chamber

28. Anaerobic jar
• Media are inoculated and then placed
in jar.
• Water is then added to gas pack
generator envelope cause evolution
of hydrogen and carbon dioxide.
• Hydrogen and oxygen react at
surface to form water to create
anaerobic condition.
• Carbon dioxide add in growth of
these bacteria.
• Indicator slip is present that change
color from blue to Colourless in
absence of oxygen.

30. Acidity or alkalinity (PH)
• For most bacteria optimum PH for growth lies between 6.5
and 7.5 while limits lie in between 5 to 9.
• However a few bacteria prefer extreme PH.
• For example Thiobacillus thiooxidan has optimum PH 2.5 to
3 however can grow in between 0.5 to 6.0 PH.
• An unclassified bacterium isolated from a stream In california
was found to grow best at PH range of 9.0 to 9.5 while could
grow within range of 8.0 to 11.4.

32. Buffer solution
• Buffer is a mixture of weak acid and conjugate base.
• Radical shift in PH can be prevented by incorporating buffer
in medium.
• Such mixtures have maximum buffering capacity at PH
where concentration of acid equals to conjugate base this PH
value is called PKa that is negative logarithm of dissociation
constant of acid.

33. • Phosphate buffer have PKa of 6.6 is widely used in
bacteriological media.
• Some nutritional ingredients such as peptones also posses
buffering capacity.
• So radical shift in PH can be prevented by incorporating
buffer.

34. Miscellaneous physical requirements
• Some bacteria have additional requirements:-
• For example photographic bacteria must be exposed to source of
illumination as light is source of energy for them.
• Bacterial growth is also influenced by hydrostatic pressure.
• As have been isolated from Deepest ocean trenches where pressure is
measured in tons per square inches.
• Many of these will not grow in laboratory conditions unless media is
subjected to similar pressure.

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