Microbial processes for ascorbic acid biosynthesis: a review.

L-Ascorbic acid is an important product currently made using the Reichstein process, which is mainly chemical. Recently, bacteria have been identified that are able to transform in a very efficient way glucose to 2,5-keto-D-gluconic acid and this product to 2-keto-L-idonic acid, precursor of L-ascorbic acid. When the corresponding strains are used together, it is possible to get 2-keto-L-idonic acid directly from glucose. Moreover, new strains have been constructed by introducing a gene from a strain responsible for the second step into a strain responsible for the first step. By using one of the new strains, the transformation can be performed in a single step with only one strain. However, the classical process still remains the most competitive.