16: TEMPERATURE EFFECTS
- Page ID
- 157084
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Describe how temperature influences the rate of biochemical reactions in bacterial cells.
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Describe the effect of small temperature shifts on bacteria with conditional lethal or non-lethal mutations.
BACKGROUND
Temperature plays a major role in the growth and survival of bacteria because it affects the speed of biochemical reactions—the chemical processes that occur inside living organisms. As temperature increases, these reactions speed up, allowing bacteria to grow and divide more quickly. However, this only continues up to a point.
Biological reactions are controlled by enzymes, which are specialized proteins that speed up chemical reactions. Enzymes have a specific three-dimensional shape that allows them to function properly. If the temperature gets too high, enzymes begin to denature (lose their shape). When this happens, the enzyme can no longer carry out its function. If the enzyme is essential for life, the bacterial cell will die.
Sometimes, the enzyme is not essential. In that case, the bacterial cell may still survive, but it may grow differently or at a slower rate because a specific function is no longer working.
A clear example of enzyme temperature sensitivity in animals can be seen in Siamese cats. These cats are pale cream in color except on their cooler body parts—such as the nose, ears, paws, and tail—which appear dark brown. This difference occurs because one of the enzymes needed to make dark pigment is temperature-sensitive. In the warmer parts of the cat’s body, the enzyme denatures and cannot function. In cooler areas, the enzyme remains active and pigment is produced, resulting in darker fur.
Bacteria also vary in the temperatures they can tolerate. Some grow on snow, while others thrive in hot springs. Each bacterial species has an optimal temperature range (the range in which it grows best). This range can help microbiologists identify and classify bacteria.
In this lab, you will investigate how temperature affects the growth of four different bacteria. Each one has a unique response to temperature:
- One strain has a conditional lethal mutation. A small temperature increase—from 34°C to 37°C—is enough to damage an essential enzyme and cause cell death.
- One is a thermophile, or heat-loving bacterium. It grows well at high temperatures like those found in hot springs. At cooler temperatures, it does not die right away, but it cannot grow.
- A third strain has a conditional non-lethal mutation. When the temperature increases slightly, one of its enzymes becomes nonfunctional. However, because this enzyme is not essential, the cells survive and grow, although they may grow differently.
- The fourth strain is a mesophile. It grows best at moderate temperatures between 25°C and 40°C, which includes room temperature and body temperature.
Your task is to observe the growth patterns of these four organisms at different temperatures to help determine which is which.
MATERIALS (Per Group of 4)
4 different bacterial cultures (A, B, C and D)
4 sterile petri dishes (1 dish per student)
1 30oC incubator
1 38oC incubator
1 55oC incubator
METHODS/PROCEDURES
1. Label your plate with your name, the date, your assigned culture letter and your assigned temperature.
2. T-streak your assigned culture on to your plate. This technique allows for isolation of colonies and will help you recognize any contaminating growth.
3. Place your inoculated plate into the labeled tub that corresponds to your assigned incubation temperature.
4. At the next lab session, your instructor will use the incubated plates to set up a set of class data for you to observe.
Print a hard copy to bring to lab (PDF).
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You are also welcome to print the PDF and turn in a physical copy of the following.
Exercise #21 Temperature Effects
NAME ______________________
EXPECTATIONS
If your culture is a thermophile. What would you expect to see after incubation at 30°C, 38°C, and 55°C? Explain why.
RESULTS
Record your observations in the table below. Record growth as either strong, weak or none. Include notes regarding any physical differences you observe such as color, texture etc.
CONCLUSIONS
1. Which culture showed the best growth at the highest temperature (55°C)? What is the does this suggest about the enzymes in that organism?
2. Which culture failed to grow at 38°C but grew well at 30°C? What type of mutation might this strain have and what is the likelihood of it being a human pathogen?
3. Which culture grew differently at 38°C compared to 30°C but was still viable. What kind of mutation does this represent? How can you tell?
4. Which culture grew well at 38°C and 30°C but did not grow at 55°C? What does this indicate about its temperature tolerance and the likelihood of it being a human pathogen?