Observation of Yeast Morphology and Identification of Live/Dead Cells

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News 16 7 月, 2025

This topic may strike a chord with many. Recently, the internet was abuzz with discussions about “fake yeast”—a term that shocked many and highlighted the unseen risks in microbial products.

Some so-called “fake yeast” products were allegedly mixed with unknown “carriers”—substances with little to no effect—resulting in diluted yeast powders that fail to deliver the expected results when used in normal quantities.

But let’s return to the main focus of this article: how to observe the morphology of yeast cells. Unlike bacteria and actinomycetes, yeast cells differ significantly in size, requiring distinct methods of observation.

1. Principle of the Experiment

Yeasts are unicellular eukaryotic organisms, typically oval or round, reproducing asexually through budding, and sometimes sexually.

Due to their relatively large size, traditional bacterial staining methods can damage yeast cells. Thus, we use direct observation, dilute iodine staining, and methylene blue staining. The methylene blue method is especially useful for distinguishing live from dead yeast cells.

Why? Because live yeast cells have strong reducing activity, which can decolorize methylene blue, making them appear colorless. Dead cells, on the other hand, retain the blue stain—enabling clear identification.

2. Preparation of Staining Solution

0.1% Loeffler’s Alkaline Methylene Blue:

Solution A: Dissolve 0.6g methylene blue in 30mL of 95% ethanol.
Solution B: Dissolve 0.01g KOH in 100mL of distilled water.
Mix Solutions A and B thoroughly.

3. Application

Observe yeast morphology.
Distinguish between live and dead cells.

4. Experimental Procedures

(1) Direct Observation Method

Place one drop of sterile water on a clean slide.
Add a small amount of yeast cells, mix gently.
Place a coverslip at a 45° angle to avoid air bubbles.
Let stand for 3 minutes and observe budding and morphology under a high-power microscope.

(2) Dilute Iodine Staining Method

Place a drop of yeast suspension on a slide.
Cover with a coverslip at a 45° angle.
Add one drop of dilute iodine on one side of the coverslip; draw it through with absorbent paper from the other side.
Let stand for 2 minutes and observe under high-power microscopy.

(3) Methylene Blue Staining Method

Place one drop of methylene blue dye on the slide.
Add a small amount of yeast cells and mix.
Cover with a coverslip, as before.
Let stand for 3 minutes, observe morphology and budding under a high-power microscope.
After 30 minutes, observe again to confirm live/dead cell status.