Role of pyruvate metabolism in the growth of Streptococcus faecalis in the presence of propionate.

The growth of Streptococcus faecalis is inhibited by propionate, and the inhibition is reversed by lipoic acid or acetate. A study of the role of pyruvate oxidation in S. faecalis showed that propionate inhibited the lipoic acid-dependent aerobic oxidation of pyruvate in resting cells. Pyruvate dehydrogenation with neotetrazolium as a hydrogen acceptor in cell-free extracts also required lipoic acid and was markedly inhibited by propionyl phosphate as well as sodium propionate. Some lipid substances, such as palmitate, oleate, behenate, and lecithin, had a lipoic acid-replacing effect on growth of the organism. Biotin or bicarbonate promoted the lipoic acid-dependent growth. Acetate-2-(14)C added to the medium was mainly incorporated into the lipid fraction of the cells. Evolution of (14)CO(2) from pyruvate-2-(14)C was not observed in resting cells of the organism, even under aerobic conditions. From the above findings, it is concluded that lipid synthesis through pyruvate oxidation plays a very important role in bacterial growth in medium containing propionate.