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Temperature Effects On The Growth Of Microorganisms

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Temperature effects on the growth of microorganisms


The purpose of this experiment was to determine the effects that temperature has on three different organisms. Temperature is one of the most important environmental factors affecting growth and survival of microorganismsІ. The three organisms used where Escherichia coli, Pseudomonas fluorescens, and Bacillus stearothermophilis. Most bacteria grow within a particular temperature range. The minimum growth temperature is the lowest temperature at which a bacterium can still grow, while the maximum growth temperature is the highest temperature at which a particular bacterium can still grow. The optimum growth temperature is the temperature at which the bacterium can grow at the highest rateâ„-. The lab group hypothesized that B. stearothermophilis would only grow at 47o C. That E. coli would grow above 13o C but stop growing above 45o C and P. fluorescens would also grow between the temperatures of 13o C and 45o C. Upon completion of incubation, results were collected as growth or no growth for each temperature.

Methods and Materials:

Figure 1a: agar plate


6 nutrient agar plates

media grown overnight in Tryptic Soy Broth

E. coli

P. fluorescens

B. stearothermophi lis

Inoculum loop Divide into 3 sections,

Incubator for 4o, 15o, RT, 30o, 35o, and 47o label each and inoculate

with all 3 organisms


Obtain six nutrient agar plates and divide each into three equal sections. (See figure 1a) Label each dish properly. Use aseptic techniqueÑ- and inoculate each dish with three different organisms. The three organisms are E. coli, B. stearothermophilis, and P. fluorescens. Each plate containing three different organisms is incubated at six different temperatures; 4o C, 15o C, room temperature, 30o C, 35o C, and 47o C for 24 hours. The incubators are controlled by the instructors. The agar plates are placed in the appropriate incubator for the corresponding temperature. After 24 hours of incubation at different temperatures data was collected. Pictures where taken by the lab group and are seen in the results section. Visual data in the form of digital photographs were collected in regards to growth or no growth.


The resulting effects of temperature on the growth of several bacteria are seen in figure 1-6. E. coli did not grow at a temperature of 4o C, however the minimum temperature of growth was 15o C and the maximum temperature was 47o C. Therefore E. coli would be considered a mesophile with the optimal growth temperature around 35o C. A mesophile is an organism living in temperatures ranging from 15o C to 47o C. B. stearothermophilis did not start to grow until 47o C, therefore would be considered a thermophile. A thermophile is an organism that thrives in hot environments. The optimal temperature for a thermophile is around 65o C, and the minimal growth temperature



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