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Pyruvate dehydrogenase activity in group N streptococci
Australian Journal of Biological Sciences
|March 1, 1980
Summary
Streptococcus lactis whole cells show pyruvate dehydrogenase activity, but cell-free extracts lack it. Different strains exhibit varied acetoin and diacetyl production from pyruvate, impacting acetate formation.
Area of Science:
- Microbiology
- Enzymology
- Biochemistry
Background:
- Pyruvate metabolism in Streptococcus lactis is crucial for dairy fermentation.
- The pyruvate dehydrogenase complex (PDC) plays a key role in pyruvate conversion.
- Understanding enzyme localization and activity is vital for optimizing starter cultures.
Purpose of the Study:
- To investigate the localization of pyruvate dehydrogenase activity in Streptococcus lactis.
- To characterize the pyruvate metabolism pathways in different Group N streptococci strains.
- To determine the factors influencing acetoin and diacetyl production.
Main Methods:
- Enzyme assays on whole cells and cell-free extracts of Streptococcus lactis.
- Identification of pyruvate dehydrogenase complex component enzymes.
- Analysis of metabolic end products (acetate, acetoin, diacetyl, butane-2,3-diol) from pyruvate.
- Comparative studies across different strains including S. lactis subsp. diacetylactis and S. cremoris.
Main Results:
- Pyruvate dehydrogenase activity was present in whole Streptococcus lactis cells but absent in cell-free extracts.
- The individual enzymes of the pyruvate dehydrogenase complex were detected in cell-free extracts.
- Acetoin and diacetyl production in Group N streptococci occurred only after acetate formation pathways were saturated.
- S. lactis subsp. diacetylactis DRC2 produced more acetoin/diacetyl and less acetate from pyruvate compared to S. lactis C10.
- Strain-specific differences in acetoin formation (via alpha-acetolactate or diacetyl) and conversion to butane-2,3-diol were observed.
Conclusions:
- Pyruvate dehydrogenase activity in Streptococcus lactis is likely cell-associated, despite the presence of its component enzymes in cell-free extracts.
- Metabolic flux towards acetate saturation influences acetoin and diacetyl production in these streptococci.
- Distinct metabolic capabilities exist among Group N streptococci strains, affecting flavor compound formation in fermented dairy products.