Unleashing the potential of microbial biosynthesis of monoterpenes via enzyme and metabolic engineering

Monoterpenes (MTPs) are valuable isoprenoids widely used in cosmetics, food flavorings, pharmaceuticals, etc. Compared to plant extraction and chemical synthesis, microbial biosynthesis offers superior sustainability and efficiency in producing natural MTPs, overcoming the limitations of raw material dependency, environmental impact, and racemic mixtures inherent in these methods. This review comprehensively discusses the development of natural or non-natural biosynthetic pathways for producing regular and irregular MTPs, emphasizing the importance of enzyme and metabolic engineering to optimize monoterpene synthases (MTPSs) in various engineered microbial cell factories (MCFs). The advances in functional expression of MTPS to enhance enzyme activity, substrate channeling of MTPS with critical biosynthesis enzymes, protein engineering of MTPS, targeted localization of MTPS in the subcellular organelle, and other favorable engineering strategies are discussed in detail. Leveraging these technologies, the engineered microbes will achieve the production of the defined product profile with higher titer/yield/productivity and improved industrial adaptability. Furthermore, we highlight the important development direction for optimizing MTPS performance and biosynthetic pathways, ensuring the microbial production of natural MTPs in a more efficient and application-specific manner.