Propionate acts as carboxylic group acceptor in aspartate fermentation by Propionibacterium freudenreichii

Cells of Propionibacterium freudenreichii ssp. shermanii and ssp. freudenreichii did not show significant growth or product formation in a mineral medium with 10 mM aspartate or 10 mM fumarate, vitamins, and a small amount (0.05% w/v) of yeast extract. In the presence of added propionate, growth with aspartate or fumarate was possible, and depended strictly on the amount of propionate provided, according to the equation: 3 aspartate + propionate 3 succinate + acetate + CO₂+3 NH₃. Cocultures of P. freudenreichii with the succinate-decarboxylating strain Ft2 converted 3 aspartate stoichiometrically to acetate and 2 propionate. High activity of methylmalonyl-CoA: pyruvate transcarboxylase, and lack of methylmalonyl-CoA decarboxylase and oxaloacetate decarboxylase activity in cell-free extracts of aspartate-grown cells indicated that failure to use aspartate as sole substrate was due to the inability of these strains to catalyze a net decarboxylation of C₄-dicarboxylic acids.Dedicated to Prof. Dr. Norbert Pfennig on occasion of his 65th birthday