Itaconic acid production from glycerol using Escherichia coli harboring a random synonymous codon-substituted 5'-coding region variant of the cadA gene.

Aspergillus terreus cadA, encoding cis-aconitate decarboxylase, is an essential gene for itaconic acid (IA) biosynthesis, but it is primarily expressed as insoluble aggregates in most industrial hosts. This has been a hurdle for the development of recombinant strategies for IA production. Here, we created a library of synonymous codon variants (scv) of the cadA gene containing synonymous codons in the first 10 codons (except ATG) and screened it in Escherichia coli. Among positive clones, E. coli scvCadA_No8 showed more than 95% of expressed CadA in the soluble fraction, and in production runs, produced threefold more IA than wild-type E. coli in Luria-Bertani broth supplemented with 0.5% glucose. In M9 minimal media containing 0.85 g/L citrate and 1% glycerol, E. coli scvCadA_No8 produced 985.6 ± 33.4 mg/L IA during a 72-h culture after induction with isopropyl β-D-1-thiogalactopyranoside. In a 2-L fed-batch fermentation consisting of two stages (growth and nitrogen limitation conditions), we obtained 7.2 g/L IA by using E. coli by introducing only the scv_cadA gene and optimizing culture conditions for IA production. These results could be combined with metabolic engineering and generate an E. coli strain as an industrial IA producer. Biotechnol. Bioeng. 2016;113: 1504-1510.