Question:
Which of the following lactic acid bacteria are capable of utilizing both leloir and tagatose pathway for their energy metabolism?
Which of the following lactic acid bacteria are capable of utilizing both leloir and tagatose pathway for their energy metabolism?
Show Hint
The Leloir pathway metabolizes free galactose, while the Tagatose-6-phosphate pathway metabolizes galactose-6-phosphate (from PEP-PTS transport). Only highly versatile dairy bacteria like Lactococcus lactis and Lacticaseibacillus casei possess both systems.
Updated On: Aug 5, 2026
- Streptococcus thermophilus and Lactobacillus helveticus
- Leuconostoc lactis and Lactococcus lactis
- Lactococcus lactis and Lacticaseibacillus casei
- Leuconostoc lactis and Lacticaseibacillus casei
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Galactose is a primary hexose sugar derived from the cleavage of lactose in milk.
Lactic acid bacteria metabolize galactose through two main biochemical pathways: the Leloir pathway and the Tagatose-6-phosphate pathway.
The pathway utilized depends on the mode of sugar transport into the bacterial cell.
Bacteria possessing both pathways have greater metabolic flexibility, allowing them to utilize free galactose and lactose-derived galactose efficiently.
Step 2: Detailed Explanation:
The Leloir pathway is the standard metabolic route for free galactose.
In this pathway, free galactose is transported into the cell and phosphorylated by galactokinase to galactose-1-phosphate, which is then converted to glucose-1-phosphate.
The Tagatose-6-phosphate pathway is active when lactose is transported via the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS).
This transport yields lactose-6-phosphate, which is cleaved into glucose and galactose-6-phosphate.
Galactose-6-phosphate is then metabolized through the tagatose pathway to form triose phosphates.
Lactococcus lactis and Lacticaseibacillus casei (formerly Lactobacillus casei) possess the complete genetic systems for both the Leloir and Tagatose-6-phosphate pathways.
This dual capability enables these species to ferment free galactose and lactose-derived galactose under varying environmental conditions.
In contrast, species like Streptococcus thermophilus are often galactose-negative or utilize only the Leloir pathway.
Step 3: Final Answer
Lactococcus lactis and Lacticaseibacillus casei are capable of utilizing both the Leloir and Tagatose-6-phosphate pathways.
Galactose is a primary hexose sugar derived from the cleavage of lactose in milk.
Lactic acid bacteria metabolize galactose through two main biochemical pathways: the Leloir pathway and the Tagatose-6-phosphate pathway.
The pathway utilized depends on the mode of sugar transport into the bacterial cell.
Bacteria possessing both pathways have greater metabolic flexibility, allowing them to utilize free galactose and lactose-derived galactose efficiently.
Step 2: Detailed Explanation:
The Leloir pathway is the standard metabolic route for free galactose.
In this pathway, free galactose is transported into the cell and phosphorylated by galactokinase to galactose-1-phosphate, which is then converted to glucose-1-phosphate.
The Tagatose-6-phosphate pathway is active when lactose is transported via the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS).
This transport yields lactose-6-phosphate, which is cleaved into glucose and galactose-6-phosphate.
Galactose-6-phosphate is then metabolized through the tagatose pathway to form triose phosphates.
Lactococcus lactis and Lacticaseibacillus casei (formerly Lactobacillus casei) possess the complete genetic systems for both the Leloir and Tagatose-6-phosphate pathways.
This dual capability enables these species to ferment free galactose and lactose-derived galactose under varying environmental conditions.
In contrast, species like Streptococcus thermophilus are often galactose-negative or utilize only the Leloir pathway.
Step 3: Final Answer
Lactococcus lactis and Lacticaseibacillus casei are capable of utilizing both the Leloir and Tagatose-6-phosphate pathways.
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