Production of citric acid from methanol by a fluoroacetate-resistant mutant of Candida sp. Y-1

Summary Fermentative production of citric acid from methanol by an isolated yeast, Candida sp. Y-1, was investigated using a medium containing fluoroacetate, a potential inhibitor of aconitase. Culture conditions were optimized, and the results showed that efficient production of citric acid required several factors; (1) the optimum concentration of fluoroacetate, (2) an addition of yeast extract with corn steep liquor, (3) a low nitrogen source concentration, and (4) strictly aerobic conditions. We then isolated a fluoroacetate-resistant mutant strain MA92 with threefold higher citric acid productivity than the wild strain. This mutant strain had lower aconitase activity than the wild strain and produced 4.6 g/l citric acid from methanol after 4 days of culture. Offprint requests to: Y. Tani