Engineering isoprenoid production

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Metabolic Engineering for Enhancing Precursor Supply for Isoprenoid Production... 

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Design and Engineer Natural Products, Methods to Isoprenoids... 

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Where natural production is not at sufficient titre and biotransformation is not a viable approach, microbes must be engineered to produce the desired isoprenoid directly from central carbon intermediates. Here we will review engineering approaches for isoprenoid production, focusing on model organisms but also discussing more unusual production strains. We also review some of the economic and practical considerations for isoprenoid bioprocesses, including issues related to feedstock price/availability (particularly important for bulk bioprocesses) and product toxicity (particularly for isoprenoid hydrocarbons with fuel applications). 

Currently, the highest titres of C5 isoprenoids reported are for isoprene, a hydrocarbon that can be polymerised to produce synthetic rubbers, elastomers and a variety of other products (Table 1). Arotmd 80 g/L can be obtained using highly engineered E. coli strains coupled with optimised bioprocess conditions (Beck et al. 2013). This titre is the highest reported in scientific literamre for any isoprenoid product so far. 

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Figure 12.2 The biosynthesis of the clavulanic acid pathway [77]. (Reproduced by permission from Macmillan Publishers Ltd M.C.Y. Chang and J.D. Keasling. Production of isoprenoid pharmaceuticals by engineered microbes. Nature Chemical Biology 2 (12) 674-682. London Nature Publishing Group. 2006 Macmillan)...

The IPP monomer serves as the universal building block for the production of all isoprenoids, including artemisinine, carotenoids, and Taxol. Thus, an engineered strain with high potential for generating IPP provides a platform for production of a variety of complex isoprenoids. The presence of two IPP synthesis pathways allows two approaches for engineering such strains. One is to introduce a heterozygous pathway and the other is to alter or modify the native pathway. Both approaches have been accomplished in E. coli. 

Lycopene is a carotenoid with anticancer properties. To improve the production of lycopene by increasing the IPP flux in an engineered E. coli, the dxs gene was overexpressed and enhanced lycopene production was obtained [45]. In another example, the native promoters of DXP pathway genes in the E. coli chromosome were replaced with the strong bacteriophage T5 promoter (PTs), and the increase in isoprenoid precursors resulted in improved /3-carotene production (with a titer of 6 mg/g dry cell weight) [44]. 

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