Abstract
Isoprenoids are diverse natural compounds, which have various applications as pharmaceuticals, fragrances, and solvents. The low yield of isoprenoids in plants makes them difficult for cost-effective production, and chemical synthesis of complex isoprenoids is impractical. Microbial production of isoprenoids has been considered as a promising approach to increase the yield. In this study, we engineered the model cyanobacterium Synechocystis sp. PCC 6803 for sustainable production of a commercially valuable isoprenoid, limonene. Limonene synthases from the plants Mentha spicata and Citrus limon were expressed in cyanobacteria for limonene production. Production of limonene was two-fold higher with limonene synthase from M. spicata than that from C. limon. To enhance isoprenoid production, computational strain design was conducted by applying the OptForce strain design algorithm on Synechocystis 6803. Based on the metabolic interventions suggested by this algorithm, genes (ribose 5-phosphate isomerase and ribulose 5-phosphate 3-epimerase) in the pentose phosphate pathway were overexpressed, and a geranyl diphosphate synthase from the plant Abies grandis was expressed to optimize the limonene biosynthetic pathway. The optimized strain produced 6.7 mg/L of limonene, a 2.3-fold improvement in productivity. Thus, this study presents a feasible strategy to engineer cyanobacteria for photosynthetic production of isoprenoids.
Highlights
Recent studies have demonstrated the potential of using cyanobacteria as biological platforms to produce fuels and high-value chemicals[1,2]
The methylerythritol 4-phosphate (MEP) pathway is a seven-step pathway that starts with glyceraldehyde 3-phosphate (GAP) and pyruvate, and ends with isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP)
Limonene is a C10 cyclic isoprenoid converted from geranyl diphosphate (GPP)
Summary
Recent studies have demonstrated the potential of using cyanobacteria as biological platforms to produce fuels and high-value chemicals[1,2]. PCC 6803 (hereafter, Synechocystis 6803) for production of a commercially valuable isoprenoid, limonene. Commercially-used isoprenoids are mainly extracted from plants, but the low quantities of these naturally-produced chemicals have become an impediment for cost-effective production. (R)-limonene has a characteristic fragrance of orange, and commonly exists in the rinds of citrus fruits It is commercially used as a fragrance in perfumes or a www.nature.com/scientificreports/. Cyanobacteria use the methylerythritol 4-phosphate (MEP) pathway to produce isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are the building blocks for isoprenoid biosynthesis. The amounts of IPP and DMAPP need to be enhanced by increasing the carbon flux toward the MEP pathway
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