Introduction and Background
The enzyme amylase is present in many living things, including bacteria, animals, and humans. The enzyme breaks down the large polysaccharide starch into smaller portions which can be broken down by other enzymes. The ability to produce amylase is not universal among bacteria, the best-known group of bacteria that can are found in the genus Bacillus. To help identify amylase-producing bacteria, Petri dishes containing agar enriched with high amounts of starch are used. Bacteria are grown on the agar and the plate is covered with Iodine after incubation. The Iodine will react with the starch in the agar, causing the Iodine to turn a dark blue color. After treatment with Iodine, the plates are examined for the following results:
- Positive for Amylase – A halo-like clearing will be present around the bacteria. The Iodine would be the normal yellow-brown color in these areas.
- Negative for Amylase – The entire area of the starch agar turns a dark blue color.
Please note that it is easy to be fooled by this experiment. Sometimes the bacterial growth may look like a positive result when you look under the plate, but what is happening is that the Iodine cannot get underneath the bacterial growth and stain the agar. Make sure you are looking on the edges of the bacterial growth for the halo-like clearings.
Laboratory Procedure
A typical procedure for this experiment would involve the following steps:
- Obtain the following materials:
- One starch agar plate
- Inoculation loop
- Bacterial culture
- Inoculate the starch agar by taking one loopful of the bacterial culture and streaking across the surface of the agar in a zig-zag pattern.
- Label the bottom of the plate and incubate the plate for 2-3 days in the designated incubation area.
- After incubation, cover the entire area of agar with Iodine and wait about 5 minutes. After waiting, carefully examine the plate to determine results and do not let the Iodine spill from the plate.
Perform the following data analysis and submit the following answers to the questions below:
Organism Name
- ?? (need name)
2. Growth? (Y/N)
yes
3. Color of medium around colonies after Iodine
dark blue
Starch Hydrolysis? (Y/N)
(yes or no??)
Organism name?
- ?? (need name)
2. Growth? (Y/N)
Yes
3.Color of medium around colonies after Iodine
White
Starch Hydrolysis? (Y/N)
(YES OR NO??)
1. When Amylase breaks down starch, name one product of the reaction.
2. Members of the genus Bacillus are known to produce Amylase. What advantage might producing Amylase provide these bacteria?
