Monoterpenes (C₁₀ isoprenoids) are the main components of essential oils and used as precursors for the synthesis of commodity chemicals and high energy density fuels. Plants are major source of these monoterpenes and recently microbial production of monoterpenes has been explored to be a promising alternative. Heterologous expression of the mevalonate (MVA) pathway and several monoterpene synthases in E. coli led to the production of various monoterpenes, but in general, the titer of microbial monoterpene production has not been as high as that of various sesquiterpenes probably due to a limited availability of C₁₀ intermediates (geranyl diphosphate, GPP) as well as the toxicity of GPP and monoterpene products.

To improve microbial monoterpene production, we heterologously expressed the MVA pathway up to GPP production, and also expressed several monoterpene synthases in E. coli. Then we used metabolomics and proteomics tools to optimize the strains. Especially, we engineered the E. coli’s native FPP synthase to improve GPP availability for monoterpene production, and from omics data analysis, we discovered that it is crucial to have a basal level of FPP to maintain growth for high titer monoterpene production as well as to achieve a high level of GPP as a precursor for monoterpenes. From this finding, our engineered strains resulted in high production of the jet fuel precursors 1,8-cineole and linalool.

The engineering strategy developed in this work will enable strains that can be used as a general platform for various monoterpenes production.