Question

Given below are two statements:
Statement (I) : Lactic acid bacteria hydrolyze casein outside the cell by cell wall bound or excreted peptidases
Statement (II) : Lactic acid bacteria hydrolyze oligopeptides into small peptides and amino acids by membrane-bound peptidases
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:

The proteolytic pathway of LAB works in three distinct steps:
1. Extracellular proteinases (cell envelope-bound) cleave casein to oligopeptides.
2. Transporters import oligopeptides into the cell.
3. Intracellular (cytoplasmic) peptidases break them down to amino acids.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lactic acid bacteria (LAB) are fastidious organisms that require pre-formed amino acids for growth.
Because milk contains very low levels of free amino acids, LAB rely on a highly complex proteolytic system to break down milk proteins (caseins) into absorbable peptides and amino acids.

Step 2: Detailed Explanation:
Let us analyze the proteolytic system of LAB:
- Statement (I) describes extracellular casein hydrolysis.
Casein molecules are too large to be transported across the bacterial cell membrane.
LAB utilize extracellular, cell envelope-bound proteinases (CEPs, such as PrtP) to hydrolyze large casein molecules outside the cell into oligopeptides.
Thus, Statement (I) is true.
- Statement (II) describes the hydrolysis of oligopeptides.
Once oligopeptides are formed outside, they are transported into the bacterial cell cytoplasm by specific active transport systems (such as the Opp system).
Once inside the cell, these oligopeptides are hydrolyzed into small peptides and free amino acids by a pool of intracellular (cytoplasmic) peptidases (such as PepN, PepC, PepX), not by membrane-bound peptidases.
Thus, Statement (II) is incorrect.
Therefore, Statement (I) is true but Statement (II) is false.

Step 3: Final Answer:
Statement (I) is true but Statement (II) is false, corresponding to option 3.