Industrial microbiology — Fungal amylases: In solid (stationary) culture using wheat bran as the substrate, which microorganism is most commonly employed for high-yield amylase production?

Introduction / Context:
Amylases are staple industrial enzymes used in starch liquefaction, brewing, baking, and syrups. Solid-state (stationary) fermentation on agricultural residues such as wheat bran is a classical, cost-effective process to obtain robust fungal amylases.

Given Data / Assumptions:

• Process type: stationary (solid-state) culture on wheat bran.
• Organisms listed: Aspergillus oryzae, Aspergillus niger, Aspergillus flavus, and Saccharomyces cerevisiae.
• Goal: pick the organism most typically used for high-yield, food-grade amylase.

Concept / Approach:
Fungal species vary in enzyme profile, secretion ability, safety status, and historical usage. Aspergillus oryzae is a long-established GRAS organism in food fermentations (koji), optimized for secreting amylases in solid substrates like wheat bran. A. niger also produces amylases but is more famous for glucoamylase and organic acids; A. flavus is disfavored due to aflatoxin risk. S. cerevisiae is primarily a fermentative yeast, not a leading amylase producer in SSF.

Step-by-Step Solution:
Identify processes that favor filamentous fungi in porous, moist solids (wheat bran). Recall that A. oryzae (koji mold) historically dominates solid-state enzyme production. Eliminate toxin-producing or non-enzyme-secreting options. Select A. oryzae as the preferred organism.

Verification / Alternative check:
Textbook and industrial practice consistently cite A. oryzae for SSF amylase on bran due to strong secretion and safe food heritage.

Why Other Options Are Wrong:

• A. niger: capable, but not the canonical choice for wheat-bran SSF amylase.
• A. flavus: safety concern (aflatoxins).
• S. cerevisiae: poor extracellular amylase secretion under SSF.

Common Pitfalls:
Confusing general enzyme producers with the specific, historic SSF organism used on wheat bran.

Final Answer:
A. oryzae