Aerobic Formation of Acetate From Pyruvate by Lactobacillus Bulqaricus

The pathway of formation of acetate from pyruvate in the homofermentative organism L. bulgaricus was studied. Three pathways for the formation of acetate were investigated. These were the formation of acetyl CoA by the pyruvate dehydrogenase (lipoate) system, the formation of acetaldehyde by pyruvate decarboxylase, and the formation of acetyl phosphate by pyruvate oxidase. The first two pathways were eliminated when it was found that the formation of acetate was not inhibited by arsenite and that acetaldehyde was not converted to acetate by L. bulgaricus. The formation of acetyl phosphate and acetate by dialysed cell-free extracts indicated the presence of pyruvate oxidase in L. bulgaricus. The pyruvate oxidase system, unlike the pyruvate dehydrogenase (lipoate) system, was not inhibited by unsaturated fatty acids. The organism was shown to possess both acetate kinase and phosphate acetyltransferase which suggested that acetyl phosphate could be converted to acetate or acetyl CoA.