Carbohydrate Metabolism by Streptococcus thermophilus : A Review

Area of Science:

• Microbiology
• Dairy Science
• Biochemistry

Background:

• Streptococcus thermophilus is a key starter culture in fermented dairy products.
• It is distinct from other lactic streptococci (Group N) in carbohydrate metabolism.
• Understanding its metabolic pathways is essential for optimizing dairy fermentation.

Purpose of the Study:

• To elucidate the carbohydrate metabolism of Streptococcus thermophilus.
• To differentiate its metabolic processes from Group N streptococci.
• To investigate the reasons behind galactose release and its implications.

Main Methods:

• Comparative analysis of carbohydrate transport systems (phosphotransferase vs. permease).
• Enzymatic assays for Leloir pathway components (galactokinase, etc.).
• Phenotypic characterization of galactose-positive and galactose-negative strains.

Main Results:

• S. thermophilus utilizes a lactose permease, not phosphotransferase, for lactose uptake.
• Glucose is metabolized, while galactose is often released extracellularly.
• Galactose fermentation occurs via the Leloir pathway in specific strains, induced by galactose.

Conclusions:

• S. thermophilus exhibits distinct lactose and galactose metabolism compared to Group N streptococci.
• Galactose release is a common trait, impacting fermentation efficiency.
• Developing S. thermophilus strains that fully ferment both glucose and galactose is a key goal.