2 - keto - l - gulonic acid is prepared from 2 , 5 - diketo - d - gluconic acid through microbial conversion . the 2 - keto - l - gulonic acid producing microorganism used for this microbial conversion includes strains which belong to genera of brevibacterium , arthrobacter , micrococcus , staphylococcus , pseudomonas and bacillus . both the incubation of the microorganism in a medium containing 2 , 5 - diketo - l - gluconic acid and the direct contact of any products obtained from the cells with a substrate containing said 2 , 5 - diketo - d - gluconic acid may be used in the disclosed process .