Question

Given below are two statements:
Statement (I) : Leuconostocs are lactic acid bacteria containing phosphoketolase.
Statement (II) : Leuconostocs metabolize lactose through 6-P-gluconate pathway and produce equimolar amount of CO\(_2\), lactate and acetate/ethanol.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Heterofermentative lactic acid bacteria (such as Leuconostoc and certain lactobacilli) contain phosphoketolase.
They always produce a mix of lactic acid, carbon dioxide, and ethanol/acetate from sugar fermentation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Lactic acid bacteria are classified as homofermentative (producing only lactic acid) or heterofermentative (producing lactic acid, carbon dioxide, and ethanol/acetate) based on their carbohydrate fermentation pathways.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Statement (I) discusses the enzyme content of Leuconostoc.
Leuconostoc species are obligate heterofermentative lactic acid bacteria.
The defining metabolic feature of heterofermentative LAB is the presence of the enzyme phosphoketolase, which is essential for cleaving pentose phosphates during fermentation.
Thus, Statement (I) is true.
- Statement (II) discusses the metabolic pathway.
Because they lack the glycolytic enzyme fructose-1,6-bisphosphate aldolase, Leuconostoc species cannot utilize the Embden-Meyerhof-Parnas (glycolytic) pathway.
Instead, they metabolize lactose and glucose via the 6-phosphogluconate pathway (or phosphoketolase pathway).
This pathway yields equimolar amounts of carbon dioxide (\( \text{CO}_2 \)), lactic acid (lactate), and ethanol/acetic acid (acetate) per molecule of glucose fermented.
Thus, Statement (II) is true.
Therefore, both Statement (I) and Statement (II) are true.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are true.