Background
When it comes to microbial growth, temperature is very important because it affects cellular enzymes. When the temperature increases, so does the enzyme activity until the three dimensional configuration of the molecules are lost, due to the denaturation of their protein structure. When temperature decreases near freezing point, enzyme inactivation occurs and cellular metabolism gradually diminishes. Bacteria, as a whole, are capable of growth within an overall temperature range of minus 5 C to 80 C. However, each species requires a narrower range that is determined by the heat sensitivity of its enzyme systems (Cappuccino 115).
Specific temperature ranges consist of the following cardinal (significant) temperature points which includes: Minimum growth temperature, Maximum growth temperature, and Optimum growth temperature. Minimum growth temperature is the lowest temperature that microbial growth will occur and below this temp, enzyme activity is inhibited and the cells are metabolically inactive so that growth is negligible or absent. Maximum growth temperature is the highest in which microbial growth will occur, and anything above this temperature will cause most cell enzymes to be destroyed and the organism will die. At Optimum growth temperature, the rate of reproduction is very rapid, however it is not necessarily ideal for all enzymatic activities of the cell (Cappuccino 115).
All bacteria can be classified into one of three major groups, depending on their temperatures requirements. Bacterial species that will grow within a temperature range of -5 C to 20 C are called Psychrophiles. The next group is called Mesphiles. These bacterial species will grow within a temperature range of 20 C to 45 C. Their distinguishing characteristic is their ability to grow at human body temperature of 37 C and their inability to grow at temperatures above 45 C. The last classification group is the Thermophiles. In this group, bacterial species will grow at 35 C and above and also have two sub groups called Facultative thermophiles and Obligate thermophiles. Facultative thermophiles include organisms that at 37 C, with an optimum growth temperature of 45 C to 60 C, and Obligate thermophiles are organisms will grow only at temperatures above 50 C, with optimum temperatures above 60 C. Therefore, the ideal temperature for specific enzymatic activities may not coincide with the optimum growth for a given organism (Cappuccino 116).
Materials and Methods
To complete this experiment, we used four Trypticase Soy agar plates and E. coli as our organism. We took the plates and made then into quadrant plates by labeling the bottom with the pencil and then labeling the lid of the plates with the name of the organism and the temperature at which the plate would be placed. The temperatures that we used were 55 C, 35 C, 22 C, and 5 C. We then aseptically inoculated each plate, by lighting the inoculation loop on the Bunsen burner and letting it cool, with E. coli, using the quadrant streak method. We repeated this method all four times with each plate. Once all inoculation was complete, we then place each plate into the correct area for the designated temperature and left them there for 24 to 48 hours.
Results
E. coli @ 22 C
E. coli @ 5 C
E. coli @ 55 C
E. coli @ 37 C
The results in this particular experiment showed us that temperature plays a significant part in the growth of an organism. A 5 C the plate was refrigerated and there was no growth on the plate. At 22 C, which was room temperature, there was a large amount of growth on the plate. At 37 C, which was body temperature, a medium amount of growth and it was also the same at 55 C as well.
Conclusion
In conclusion, we’ve learned in this lab that temperature plays a big role in the growth of an organism. We found out that if an organism is refrigerated right away, that minimal or no growth will occur. At room temperature, there was a massive amount growth letting us know that 22 C was the most effective temperature when it comes to E. coli. Growth at 37 C and 55 C were both pretty consistent, and those temperatures were effective with the medium amount of growth on the plates. We now understand the importance of temperature on the growth of an organism and keeping organisms alive.
Review Questions:
1. In the following chart, indicate the types of organisms that would grow preferentially in or on various environments, and indicate the optimum temperature for their growth.
Environment Type of Organism Optimum Temperature
Ocean bottom near shore Mesophile 25 degrees Celsius
Ocean bottom near hot vent Thermophile 35 degrees Celsius
Hot sulfur spring Thermophile 45 degrees Celsius
Compost pile (middle) Mesophiles 37 degrees Celsius
High mountain lake Psychrophiles 5 degres Celsius
Center of an abscess Mesophile 42 degrees Celsius
Antarctic ice Psychrophiles -5 degrees Celsius
2. Explain the effects of temperatures above the maximum and below the minimum growth temperatures on cellular enzymes.
If the temperature is above the maximum then the cellular enzymes run the risk of denaturing. If the temperature is below the minimum growth temperature then the speed of reaction will be diminished due to the slow movement of molecules that participate in the reaction.
3. If an organism grew at 20 degrees Celsius, explain how you would determine experimentally whether the organism was a psychrophile or or a mesophile.
The test would consist of preparing two cultures of the organism on streak plates and incubating one plate at 37 degrees Celsius and the other one at 5 degrees Celsius. If growth occurs at 37 degrees Celsius then the organism is a mesophile. If growth occurs at 5 degrees Celsius then the organism is a psychrophile.
4. Is it possible for a thermophilic organisms to induce infections in warm blooded animals? Explain.
It is possible for a thermophilic organism to induce infections in warm blooded animals since thermophiles can grow at 37 degree Celsius and have optimum growth at 40 to 50 degrees Celsius.
Works Cited
Cappuccino, James, and Natalie Sherman. Microbiology: A Laboratory Manual. Tenth Edition. Boston: Pearson, 2014. Print.
Last updated on 7-April-2014 at 8:01 PM
Microbiology in Review 