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Related Experiment Videos

Galactokinase activity in Streptococcus thermophilus.

R Hutkins, H A Morris, L L McKay

    Applied and Environmental Microbiology
    |October 1, 1985
    PubMed
    Summary

    Streptococcus thermophilus possesses galactokinase (galK), an enzyme crucial for galactose metabolism. Enzyme activity is significantly higher in galactose-fermenting strains, suggesting a key role in their ability to utilize this sugar.

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    Area of Science:

    • Microbiology
    • Enzymology
    • Biochemistry

    Background:

    • Streptococcus thermophilus is a key bacterium in dairy fermentation.
    • Galactose metabolism is essential for certain bacterial strains.
    • Understanding galactose utilization pathways is important for optimizing fermentation processes.

    Purpose of the Study:

    • To investigate the presence and activity of galactokinase (galK) in Streptococcus thermophilus.
    • To compare galK activity between galactose-fermenting (Gal+) and non-fermenting (Gal-) strains.
    • To elucidate the regulatory mechanisms of galK expression in S. thermophilus.

    Main Methods:

    • Assessing ATP-dependent phosphorylation of [14C]galactose.
    • Enzyme activity assays for galactokinase (galK).
    • Culturing S. thermophilus strains under different conditions (lactose, galactose) and analyzing enzyme induction/repression.

    Main Results:

    • All 11 tested S. thermophilus strains possessed galactokinase (galK).
    • Gal+ strains exhibited 10-fold higher galK activity compared to Gal- strains.
    • Gal- strains released galactose and could not induce galK, while Gal+ strains showed inducible galK expression linked to galactose availability.

    Conclusions:

    • Galactokinase (galK) is present in S. thermophilus and its activity correlates with galactose fermentation ability.
    • GalK expression in Gal+ S. thermophilus is regulated by an induction-repression mechanism, responsive to substrate availability.
    • Gal- S. thermophilus strains lack the ability to induce galK, hindering galactose utilization.

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