The physical factors affects the growth of microorganism. 1) Temperature Temperature is the most important factor that influences the rate of enzyme catalysed reactions and rate of growth. For every organisms there is an optimum temperature for growth and minimum temperature for inhibiting the growth. Most extreme the microbes need liquid water to grow.(330C). some algae and fungi grow at 55-60 degreeC. Prokaryotes are grow at 100 degreeC. Based on temperature the microorganisms are classified into two 4.

1. Sijo.A
B.sc.Botany & Biotechnology
Mar ivanios college
Tvm, Kerala

2.  The physical factors affects the growth of microorganism.
1) Temperature
 Temperature is the most important factor that influences the
rate of enzyme catalysed reactions and rate of growth.
 For every organisms there is an optimum temperature for
growth and minimum temperature for inhibiting the growth.
 Most extreme the microbes need liquid water to grow.(330C).
 some algae and fungi grow at 55-60 degreeC.
 Prokaryotes are grow at 100 degreeC.
 Based on temperature the microorganisms are classified into
two 4.

3. i) psychrophiles
 They are grow at zero degree celcius.
 They isolated from arctic and antarctic habitats.
Because 90% is ocean.
 The cell membrane of psychrophilic microorganisms
have high levels of unsaturated fatty acid and remain
semifluid when cold.
 If temperature is more than 15 degree celcius the cell
membrane will disrupts.
 Eg: Pseudomonas vibrio

4. 2) Mesophiles
 They are grow at 20-45 degree C.
 Almost all human pathogens are mesophiles.
 Eg:cyanobacteria(Nostoc, Anabaena, Oscillatoria etc.)
3) Thermophiles
 They are grow at 45-65 degree C.
 They have more heat stable enzymes and protein
synthesis system able to function at high temperature.
 Eg: Thermus aquaticus.
4) Hyper thermophiles
 They are grow at 80-100 degree celcius.
 They found in the hot areas of sea floor.
 Eg: Pyrococcus abysi

5. 2) Oxygen requirements
i) Aerobic bacteria  they require O2 for growth. Eg:
pseudomonas.
ii) Anaerobic bacteria they do not need O2 for growth.
Eg: Streptococcus pyogenes
iii) Facultative anaerobic bacteria they can grow in
presence or absence of oxygen. Eg: Yeast.
iv) Microaerophilic bacteria they require low level of
oxygen. The high level of O2 is toxicant to the microbes.
Eg: campylobacter.

6. 3) pH
 The pH is defined as the negative logarithm of hydrogen
ion concentration.
 Microbial growth and activity are affected by the pH of
the medium.
 Microorganisms frequently change their pH by
producing acidic or basic metabolic waste products.
 Fermentative microorganisms forms organic acids from
carbohydrates, where as chemolithotrophs like
Thiobacillus oxidise reduced sulfur into sulfuric acid.
 Other microorganism make their environment more
alkaline by generating ammonia through aminoacid
degradation.

7.  Based on pH microorganisms are classified into three.
1) Acidophile
 They can survive at pH 0 and 0.5
 Eg: picrophilus.
2) Neutrophile
 They can survive at Ph 5.5 & 8.0
3) Alkalophile
 They can survive at Ph 8.5 & 11.5
 Eg: nitrobacteria.
4) Light
 The photosynthetic microorganisms such as
cyanobacteria, microalgae and photosynthetic bacteria
need light for energy production.

8. 5) salt concentration & water activity
 Based on these factors the microbes are classified into 2.
1) Halphile
 They require high level of Nacl to grow.
 Eg: halobacterium
2) Osmophile
 They require wide range of water activity.
 Eg: Stephallococcus aureus.

9.  THANK YOU…….