Lab: Identification Of Fungi
Laboratory Exercise #5
Identification of Fungi
Fungi, like bacteria, may be useful in industry but also problematic. Many produce important products including foods, chemicals, enzymes and pharmaceuticals such as antibiotics and hormones. Molds, however, in particular, are also common contaminants in industry. It is important to be able to recognize and identify them, therefore, in the laboratory.
In today’s laboratory session you will examine some common molds and attempt to identify them. While the identification of bacteria relies heavily on biochemical testing, the identification of molds tends to focus on their structural features. You will examine the appearance of growing cultures of several different molds and then prepare wet …show more content…
mounts of each to examine microscopically. Your instructor will provide you with a ‘key’ which includes information regarding some of the more common molds. You will use this key to identify the lab isolates. You will also prepare wet mounts of a yeast culture and use the ocular micrometer of your microscope to measure these cells for comparison to bacterial cells.
Part A: Molds
Method: 1. Obtain an agar plate culture of an ‘unknown’ mold. All molds have been cultured on Sabouraud’s dextrose agar (SDA).
2.
Visually examine the culture. A dissecting (or stereo-) microscope may be useful for this purpose.
Record: a. colour or pigmentation of the culture b. texture (powdery, viscous, etc.)
3. Obtain a clean microscope slide and add 1-2 drops of lactophenol cotton blue (stain) to it.
4. Obtain a short piece of cellophane tape. Be careful to touch it only at the two ends.
5. Press the ‘sticky side’ down onto the surface of the mold culture. If there are different colours present in the culture, try to ‘pick up’ a portion of each. Spores may be a different colour than the mycelia – usually darker. Remember that you want to keep the reproductive structure (the part of the mold where the spores are located) intact.
6. Place the tape ‘sticky side’ down onto the drop of lactophenol cotton blue on the microscope slide prepared in Step 3. Try to keep the tape smooth; avoid ‘wrinkles’ or folds if possible.
7. Examine the slide using the light microscope. Start by using low and medium power to locate the reproductive structures. Higher magnifications may then be used for more detailed observations.
8. Draw a diagram of the mold structure. Are the mycelia septate or non-septate? Record the stain and magnification
used.
9. Consult the key provide by your instructor. Identify the possible genus (or genera) for each of the provided unknowns.
Part B: Yeast
Method: 1. Obtain a broth culture of Saccharomyces cerevisiae (baker’s yeast).
2. Add a few drops of this culture to a clean microscope slide together with a drop or two of the lactophenol cotton blue dye. Place a cover slip over the preparation.
3. Examine the yeast cells using the light microscope. Can you see any budding cells?
4. Draw a diagram to illustrate the structure of a typical yeast cell.
5. Use the ocular micrometer to estimate the size of the yeast cells. Assume that the length of one ocular division is approximately 2.5 m for the 40x lens and approximately 1.0 m for the 100x (oil immersion) lens. Note that yeast cells are oval; as such, the length and width (diameter) must both be determined. Take the average of three cells.
Complete the provided worksheet
Identification of Fungi
Fungi, like bacteria, may be useful in industry but also problematic. Many produce important products including foods, chemicals, enzymes and pharmaceuticals such as antibiotics and hormones. Molds, however, in particular, are also common contaminants in industry. It is important to be able to recognize and identify them, therefore, in the laboratory.
In today’s laboratory session you will examine some common molds and attempt to identify them. While the identification of bacteria relies heavily on biochemical testing, the identification of molds tends to focus on their structural features. You will examine the appearance of growing cultures of several different molds and then prepare wet …show more content…
mounts of each to examine microscopically. Your instructor will provide you with a ‘key’ which includes information regarding some of the more common molds. You will use this key to identify the lab isolates. You will also prepare wet mounts of a yeast culture and use the ocular micrometer of your microscope to measure these cells for comparison to bacterial cells.
Part A: Molds
Method: 1. Obtain an agar plate culture of an ‘unknown’ mold. All molds have been cultured on Sabouraud’s dextrose agar (SDA).
2.
Visually examine the culture. A dissecting (or stereo-) microscope may be useful for this purpose.
Record: a. colour or pigmentation of the culture b. texture (powdery, viscous, etc.)
3. Obtain a clean microscope slide and add 1-2 drops of lactophenol cotton blue (stain) to it.
4. Obtain a short piece of cellophane tape. Be careful to touch it only at the two ends.
5. Press the ‘sticky side’ down onto the surface of the mold culture. If there are different colours present in the culture, try to ‘pick up’ a portion of each. Spores may be a different colour than the mycelia – usually darker. Remember that you want to keep the reproductive structure (the part of the mold where the spores are located) intact.
6. Place the tape ‘sticky side’ down onto the drop of lactophenol cotton blue on the microscope slide prepared in Step 3. Try to keep the tape smooth; avoid ‘wrinkles’ or folds if possible.
7. Examine the slide using the light microscope. Start by using low and medium power to locate the reproductive structures. Higher magnifications may then be used for more detailed observations.
8. Draw a diagram of the mold structure. Are the mycelia septate or non-septate? Record the stain and magnification
used.
9. Consult the key provide by your instructor. Identify the possible genus (or genera) for each of the provided unknowns.
Part B: Yeast
Method: 1. Obtain a broth culture of Saccharomyces cerevisiae (baker’s yeast).
2. Add a few drops of this culture to a clean microscope slide together with a drop or two of the lactophenol cotton blue dye. Place a cover slip over the preparation.
3. Examine the yeast cells using the light microscope. Can you see any budding cells?
4. Draw a diagram to illustrate the structure of a typical yeast cell.
5. Use the ocular micrometer to estimate the size of the yeast cells. Assume that the length of one ocular division is approximately 2.5 m for the 40x lens and approximately 1.0 m for the 100x (oil immersion) lens. Note that yeast cells are oval; as such, the length and width (diameter) must both be determined. Take the average of three cells.
Complete the provided worksheet