Pyruvate dehydrogenase activity in group N Streptococci.

Pyruvate dehydrogenase activity was detected in whole cells but not in cell-free extracts of Streptococcus lactis. However, the three component enzymes (pyruvate decarboxylase, lipoate acetyltransferase and lipoyl dehydrogenase) of the pyruvate dehydrogenase complex were identified in the cell-free extracts. Whole cells of the three species of group N streptococci formed acetoin and diacetyl only after the pathway forming acetate had become saturated. S. lactis subsp. diacetylactis DRC2 formed more acetoin and diacetyl and less acetate from pyruvate than did S. lactis CW. Strains CIO and DRC2 were able to form acetoin via a-acetolactate or diacetyl and to convert acetoin to butane-2,3-diol. S. cremoris HP was able to form acetoin only via a-acetolactate and could not convert acetoin to butane-2,3cdiol.