Biosynthesis of adipic acid by a highly efficient induction-free system in Escherichia coli

Adipic acid is an important dicarboxylic acid, which is an essential building block to synthesize nylon 6-6 fiber. Adipic acid is primarily synthesized from chemical plant, however, this process is associated with a number of environmental concerns including heavy pollution, toxic catalyst and harsh reaction conditions. A decent amount of adipic acid was produced by reconstructing the reversed adipate-degradation pathway (RADP) from Thermobifida fusca in Escherichia coli. However, IPTG was used in the previous study, which was not feasible in the fermentation industry. In this study, strong promoter-5'-UTR complexes (PUTR) were chosen to construct a highly efficient induction-free system to produce adipic acid. First, comparisons of various exogenous 5'-UTR Complexes, as well as a series of E. coli host strains, demonstrated that those genes using E. coli K12 MG1655 as the host strain produced the highest titer of adipic acid. Subsequently, optimizations were applied to enhance the titer of adipate biosynthesizing strains. The highest titer of adipate of 57.6 g L^-1 was achieved by fed-batch fermentation. This work offers a better way to enhance the industrial titer of adipate.