Comparing ethanologens: Why does Zymomonas (for example, Zymomonas mobilis) offer advantages over yeast in certain high-sugar ethanol fermentations?
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AIt tolerates higher osmotic pressure from concentrated sugars
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BIt exhibits higher ethanol tolerance under some conditions
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CIt has a higher specific sugar uptake and growth rate (Entner–Doudoroff pathway)
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Zymomonas mobilis is an alternative ethanologen to Saccharomyces cerevisiae. Its physiology offers benefits in specific process scenarios, especially with high sugar concentrations and target high ethanol titers.
Given Data / Assumptions:
- High-gravity fermentations with elevated osmolarity.
- Goal: rapid conversion and high ethanol yield.
- Comparison with conventional yeast performance.
Concept / Approach:Zymomonas uses the Entner–Doudoroff pathway, enabling high specific sugar uptake and ethanol productivity. It can tolerate high osmotic pressures and substantial ethanol concentrations in certain settings, making it competitive for specific substrates and conditions.
Step-by-Step Solution:
List physiological advantages: osmotic tolerance, ethanol tolerance, high specific rates.Confirm they translate to process benefits (productivity, final titer).Select the inclusive option “All of the above.”Verification / Alternative check:Applied microbiology literature documents Zymomonas advantages in high-gravity fermentation, while noting limitations (substrate range, nutrient needs).
Why Other Options Are Wrong:
Individual advantages alone understate the multi-factor benefits.“None” contradicts documented performance features.Common Pitfalls:Assuming Zymomonas universally outperforms yeast; strain engineering and substrate composition matter.
Final Answer:All of the above.