Introductory Microbiology

Factors affecting growth and growth rates

1) Temperature
2) pH
3) Oxygen requirement
4) Osmotic pressure

1) Temperature:
The growth rate of microorganisms falls abruptly at high temperatures is caused by the thermal denaturation of enzymes. Every organisms, has a minimum, maximum and optimum temperature for growth. On the basis of temperature, microorganisms are divided into:
1) The psychrophiles – 0-50C
2) The mesophiles – 20-450C
3) The thermophiles _ > 550CM

2) pH:
• Many yeasts and molds and certain bacteria grow well in acidic media (5.00 or below) while most bacteria require a pH of near neutrality (6.5-8.0) for optimal growth. The pH of the medium profoundly affects the growth of microorganisms, since enzymes are sensitive to alterations in pH.

3) O2 requirement:
• Growth rate of microorganisms depends on optimum aeration conditions. Aerobes depend on O2 whereas anaerobes sensitive to O2 and grow in the absence of O2. In between there are facultative anaerobes which can grow either in the presence or in the absence of O2.

4) Osmotic pressure:
• All organisms do not need a high sugar or salt concentration for optimal growth. Some yeasts and molds grow in medium containing a high concentration of sugar are called as ‘osmophiles’. Certain bacteria of marine origin require high concentration of NaCl (>20%) for their optimal growth and these are termed as’ halophiles’.