L-Malic acid fermentation by mixed culture of Rhizopus arrhizus and Proteus vulgaris.

When Rhizopus arrhizus NRRL 1526 was mix-cultured with Proteus vulgaris AHU 1144, a strain having a high fumarase activity, in a medium containing glucose as a substrate, fumaric acid fermentation was successively converted to L-malic acid fermentation and large amounts of L-malic acid were accumulated as an end product. As an inoculum of P. vulgaris for this fermentation, cells in the stationary growth phase (48 to 72 hr culture) were much more favorable than those in the exponential growth phase (18 hr culture) and malic acid yields in the former case were as high as about 70 to 75% based on initial glucose after 3 to 4 days of the mixed culture.