(752c) Engineering of a Highly Efficient Escherichia coli Strain for Mevalonate Fermentation

To reduce the reliance on fossil input, metabolic engineering has been developed to produce environmentally friendly and cost effective bio-chemicals from sustainable materials. However, few of the bio-based chemicals are commercially competitive with the conventional petroleum-derived materials. We engineered an Escherichia coli strain to produce cost effective mevalonate, the precursor of β-methyl-δ-valerolactone for the production of mechanically tunable polyesters. To prevent the extra metabolic burden and genetic instabilities related with plasmid-based fermentation, the mevalonate pathway driven by a constitutive promoter was integrated into the chromosome of E. coli to replace the native fermentation gene adhE or ldhA. The engineered strains (CMEV-1 and CMEV-2) did not require inducer or antibiotic, and showed slightly higher maximal productivities (0.38 ~ 0.43 g/L/hr), and yields (67.8 ~ 71.4 % of the maximum theoretical yield) than those of the plasmid-based fermentation. Since the glycolysis pathway is the first module for mevalonate synthesis, atpFH deletion was employed to improve the glycolytic rate, and the production rate of mevalonate. Shake flask fermentation results showed the deletion of atpFH in CMEV-1 resulted in a 2.1-fold increase in the maximum productivity. Finally, our fed-batch fermentation showed that, with the deletion of atpFH and sucA genes and integration of two copies of the mevalonate pathway genes into the chromosome, the engineered strain CMEV-7 exhibited both high maximal productivity (~ 1.01 g/L/hr) and high yield (86.1 % of the maximum theoretical yield, 30 g/L mevalonate from 61 g/L glucose after 48 hours in shake flask). This result also provides an example on how to tune the carbon flux for optimal production of exogenous chemicals.