Effect of temperature on growth of bacteria

Aim

To study the effect of temperature on growth of bacteria

Principle

Temperature is one of the most important physical factors influencing the growth of microorganisms. Bacteria unlike eukaryotes lack homeostatic mechanism and they do not regulate the heat generated by metabolism, thus are affected readily by changes in temperature. Enzymatic reactions have maximum efficiency at optimum temperature which varies with organisms. For every 10⁰C rise in temperature, there is two-fold increase in the rate of enzyme catalyzed reactions for a limited range of temperature. At high temperatures, proteins are irreversibly denatured and there is a total enzyme destruction. At low temperature, the enzyme reactions are merely inactivated and are thus less harmful.

Bacteria are divided into three major groups with respect to their temperature requirements:

1)      Psychrophiles - with optimum temperature between 0 and 20⁰C

2)      Mesophiles - with optimum temperature between 20 and 40⁰C

3)      Thermophiles - with optimum temperature between 40 and 60⁰C

Temperature in the range between 50⁰C and 100⁰C are normally lethal for bacterial cells.  The range of temperature preferred by a bacterial is genetically determined.  Each organism grows within a particular temperature range, that is cardinal temperature points.  The minimum growth temperature is the lowest temperature at which the growth will occur and maximum growth temperature is the highest temperature at which the organism can grow.  The optimum growth temperature is the one at which organism grows fastest.

 

Materials required

1.      Culture of E coli and Bacillus sp

2.      Sterile Nutrient broth tubes

3.      Equipments - bunsen burner, inoculating needle, refrigerator, Incubator

Procedure

1.      Each nutrient broth tube was labelled with the temperature (4⁰C, 20⁰C, 37⁰C, 50⁰C) and organism to be inoculated.

2.      The tubes were inoculated with E coli and Bacillus sp

3.      Tubes were incubated at different temperatures for 24 hours

4.      The tubes were observed and the optical density was recorded at 600 nm

 

Observation and result

The result is tabulated. The bacterial species were found to have different growth patterns at different incubation temperatures.  The optimum temperature with maximum growth was found to be 37⁰C for E coli and 37⁰C for Bacillus sp

 

 

Effect of temperature on bacterial growth (left hand side)

Organism	OD at 600 nm
	40C	200C	370C	500C
E coli	0.005	0.22	0.38	0.00
Bacillus sp	0.00	0.23	0.32	0.01