Isoprene production by Escherichia coli through the exogenous mevalonate pathway with reduced formation of fermentation byproducts

Background: Isoprene, a volatile C5 hydrocarbon, is an important platform chemical used in the manufacturing of synthetic rubber for tires and various other applications, such as elastomers and adhesives. Results: In this study, Escherichia coli MG1655 harboring Populus trichocarpa isoprene synthase (PtispS) and the exogenous mevalonate (MVA) pathway produced 80 mg/L isoprene. Codon optimization and optimal expression of the ispS gene via adjustment of the RBS strength and inducer concentration increased isoprene production to 199 and 337 mg/L, respectively. To augment expression of MVA pathway genes, the MVA pathway was cloned on a high-copy plasmid (pBR322 origin) with a strong promoter (P-trc), which resulted in an additional increase in isoprene production up to 956 mg/L. To reduce the formation of byproducts derived from acetyl-CoA (an initial substrate of the MVA pathway), nine relevant genes were deleted to generate the E. coli AceCo strain (E. coli MG1655 Delta ackA-pta, poxB, ldhA, dld, adhE, pps, and atoDA). The AceCo strain harboring the ispS gene and MVA pathway showed enhanced isoprene production of 1832 mg/L in flask culture with reduced accumulation of byproducts. Conclusions: We achieved a 23-fold increase in isoprene production by codon optimization of PtispS, augmentation of the MVA pathway, and deletion of genes involved in byproduct formation.