Pyruvate-decarboxylase (Pdc)-negative Saccharomyces cerevisiae has been reported to grow in batch cultures on glucosecontaining complex media, but not on defined glucose-containing media. By a combination of batch and chemostat experiments it is demonstrated that even in complex media, Pdc 3 S. cerevisiae does not exhibit prolonged growth on glucose. Pdc 3 strains do grow in carbon-limited cultures on defined media containing glucose-acetate mixtures. The acetate requirement for glucose-limited growth, estimated experimentally by continuously decreasing the acetate feed to chemostat cultures, matched the theoretical acetyl-CoA requirement for lipid and lysine synthesis, consistent with the proposed role of pyruvate decarboxylase in the synthesis of cytosolic acetyl-CoA. z

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