Cell-free extracts of group D streptococci incorporated14CO2into aspartate. Pyruvate was the acceptor of CO2forStreptococcus faecium; phosphoenolpyruvate was the CO2acceptor forS.bovis; and both substrates were CO2acceptors forS.faecalis. The enzymes, by which the CO2fixation was effected, appear to be pyruvate carboxylase forS.faecium, phosphoenolpyruvate (PEP) carboxykinase and PEP carboxylase forS.bovis, and pyruvate carboxylase and PEP carboxykinase forS.faecalis.