127. A microbial community has grown on starch anaerobically and it produced a mixture of metabolites with the
following composition: glucose, disaccharides, acetate, butyric acid, butanol and carbon dioxide. This
microbial community is comprised of:
1. E. coli, Clostridium, Methanosarcina
2. E. coli, Bacillus, Saccharomyces
3. Acetobacter, Bacillus, Methanosarcina
4. Methanosarcina, Methanococcus, E. coli

Question Recap

A microbial community growing anaerobically on starch produces:

• Glucose

• Disaccharides

• Acetate

• Butyric acid

• Butanol

• Carbon dioxide

Which of the following communities best explains this mixture?

Step-by-Step Analysis

1. Starch Breakdown

• Starch is a polysaccharide made of glucose.

• Initial breakdown by amylases releases glucose and disaccharides.

• This step is common in many bacteria including E. coli and Clostridium.

2. Fermentation Products

The key anaerobic products observed:

• Acetate, butyric acid, butanol, CO₂

  • These are classic products of anaerobic fermentation by Clostridium spp.

  • Clostridium is known for its butyric acid and butanol production (e.g., Clostridium acetobutylicum).

3. Carbon Dioxide

• A common by-product of fermentation.

• Supports activity of both fermentative bacteria and methanogens.

4. Methanosarcina

• An archaeon involved in methanogenesis, typically found in anaerobic microbial consortia.

• Can use acetate or CO₂ to produce methane, indicating it’s part of a syntrophic anaerobic system.

5. E. coli

• Facultative anaerobe.

• Can survive anaerobic environments and contribute to disaccharide/glucose fermentation, though it’s not a major butyric acid or butanol producer.

✅ Correct Answer: 1. E. coli, Clostridium, Methanosarcina

• E. coli: Initial starch hydrolysis and basic fermentation

• Clostridium: Produces acetate, butyric acid, and butanol

• Methanosarcina: Utilizes by-products for methanogenesis, completing the anaerobic cycle

Conclusion

The observed metabolite profile strongly suggests a syntrophic community:

• Clostridium handles the heavy anaerobic fermentation.

• E. coli initiates breakdown.

• Methanosarcina finalizes the process with methane production (though not mentioned explicitly, its role is inferred by presence of CO₂ and acetate).

This synergy is essential in anaerobic digestion systems, like those in biogas production or anaerobic wastewater treatment.