What is the microbial source of the enzyme cellulase?

Explanation

**Step-by-Step Text Solution:**

1. **Identify the Enzyme**: The enzyme in question is cellulase, which is responsible for breaking down cellulose into simpler sugars, primarily beta-glucose.

2. **Recognize the Microbial Sources**: Cellulase is produced by various microorganisms, including fungi, bacteria, and protozoans.

3. **Specify the Key Microbial Source**: Among these microorganisms, a notable source of cellulase is the fungus Trichoderma, specifically the species Trichoderma reesei.

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