Ethanol manufacture: Production from starch-rich and raw sugar feedstocks commonly employs selected strains of which microorganism?

Introduction / Context: Commercial alcohol production relies on robust ethanologens capable of high ethanol yields, osmotolerance, and inhibitor tolerance. The organism choice depends on substrate (starch vs sugars) and process conditions.

Given Data / Assumptions:

• Feedstocks include starch-derived hydrolysates and raw sugars such as molasses.
• We are to identify the standard industrial organism used worldwide.

Concept / Approach: Saccharomyces cerevisiae is the classic yeast for brewing and fuel ethanol. It efficiently ferments glucose, fructose, and sucrose, tolerates high ethanol, and operates over a broad pH and temperature range. Candida species have niche uses (e.g., lactose fermentation or SCP), but are not the mainstream choice for starch/sugar ethanol plants.

Step-by-Step Solution: Match core industrial trait: high ethanol yield and tolerance → S. cerevisiae. Candida utilis: renowned for single-cell protein, not primary ethanol fermenter from these feedstocks. Candida pseudotropicalis: specialized lactose fermentations; less common in standard sugar/starch plants. Therefore select Saccharomyces cerevisiae.

Verification / Alternative check: Distillery and fuel ethanol literature consistently cites S. cerevisiae for molasses and starch hydrolysates; Zymomonas mobilis is used in select processes but is not the default in many industrial molasses/starch operations.

Why Other Options Are Wrong: They lack the broad, routine industrial deployment for these substrates or are used for different purposes.

Common Pitfalls: Overgeneralizing niche organisms; industrial constraints (tolerance, contamination resistance) favor Saccharomyces.

Final Answer: Saccharomyces cerevisiae.