Microbial production of limonene and its derivatives: Achievements and perspectives.

Limonene and its derivatives have great market potential with diverse applications in food, pharmaceuticals, cosmetics, etc. Commercial production of limonene and its derivatives through extraction from plants suffers from the unstable market supply, while chemical synthesis of these compounds is hindered by high energy consumption and pollutant emission. Microbial biosynthesis provides a promising alternative approach for the sustainable supply of limonene and its derivatives. However, low efficiency and specificity of the biosynthetic enzymes and pathways in heterologous hosts make it still challenging for the commercialization of microbial limonene production. On the other hand, the limonene toxicity heavily reduces cellular fitness, which poses a serious challenge for improving limonene titer. Here, we critically review the recent progresses in engineering microbes for limonene biosynthesis and derivation with the emphasis on enzyme characterization and pathway optimization. In particular, we introduce the current trends in microbial limonene decoration for the biosynthesis of bio-active molecules such as α-terpineol and perillyl alcohol. We also discuss the feasible strategies for relieving limonene toxicity and enhancing the robustness of microbial cell factories.