Question

1. Compare and contrast homolactic acid fermentation and heterolactic acid fermentation. How do these compare to glycolysis/entner-douderoff pathways?

2. How do lactic acid bacteria affect their environment after they have fermented lots of glucose, and what adaptations might they have to overcome that effect

Answer 1

1.

• Homolactic acid fermentation converts glucose to 2 molecules of lactic acid. Heterolactic acid fermentation converts glucose to lactic acid, ethanol, and CO₂.
• Example for homo-lactic acid fermenter is Lactobacillus delbrueckii. Example for hetero-lactic acid fermenter is Leuconostoc mesenteroids.
• The enzyme aldolase is involved in homolactic acid fermentation. This enzyme is not produced by hetero-lactic acid fermenter.
• Lactic acid fermentation mostly occurs in anaerobic condition. Glycolysis and entner-douderoff pathway takes place mostly in aerobic condition.
• Homolactic fermentation, glycolysis, and entner-douderoff pathway produce 2 molecules of pyruvate as the end product. Heterolactic fermentation produces one pyruvate and one acetaldehyde. These pathways differ in the enzymes involved.
• The entner-douderoff pathway uses 6- phosphogluconate dehydratase and 2-keto-3-deoxy phosphogluconate aldolase. These enzymes are not involved in glycolysis.
• In the entner-douderoff pathway, one glucose molecule yield 1ATP, 1 NADH and 1 NADPH. In glycolysis, one molecule of glucose yield 2 ATP and 2 NADH.

2.

• Lactic acid bacteria produce lactic acid, ethanol, and CO₂. Once it fermented lots of glucose, there will be a change in the pH and nutrient availability.
• There will be an acidic environment, high ethanol concentration and less number of glucose substrate which won't be favorable for the bacteria to live.
• The bacteria begin to adapt to this unfavorable condition. They will become cyst-like dormant cells.
• They make a change in the lipid composition of their membrane. There will be an increased ratio of saturated to unsaturated fatty acids in the membrane in order to resist the acidic condition.
• Also, there will be changes in their metabolic reactions. Due to the starvation stress, they catabolize the amino acids to form long-chain fatty acids.