The mutants used in this study, Sphingobacterium sp. M4113/M4115, were originated from a wild-type strain GCG, which was isolated from the sewage of a styrene monomer-manufacturing factory. The culturing medium contains appropriate amounts of K2HPO4, (NH4)2SO4, MgSO4·7H2O, Na-succinate, yeast extract and EDTA–FeCl3 complex. The highest conversion yield was obtained with mutant strain M4115, in which more than 0.560 g of cis,cis-muconic acid was accumulated in 28 h from a Na-benzoate solution of 2.0 g/l (∼28% yield). Growth inhibition appeared as the concentration of Na-benzoate exceeded 3.0 g/l. In addition, an increase of 17% and 6% of cis,cis-muconic acid in yield were observed for M4115 and M4113, respectively, as EDTA–FeCl3 complex was employed. It's believed that this complex can enhance the yield of catechol 1,2-dioxygenase, and therefore, the yield of cis,cis-muconic acid according to β-ketoadipate biosynthesis pathway.
