This technology can be used to develop commercially viable methods for the biosynthesis of isoprenoids, including the valuable chemotherapeutic agent paclitexal (Taxol).
In its early days, paclitaxel was harvested from the bark of the European yew -- a destructive process that results in the death of the tree. Concerns over sustainability and drug availability have fueled interest in alternative sources of paclitaxel, which recently led to the development of microbial strains that possess full biosynthetic pathways for isoprenoids including paclitaxel. However, these pathways have only been implemented in single cells to date. This places a large burden on the gene expression machinery of the host cell, which complicates genetic cloning and limits the utility of such technology for commercial production of isoprenoids. This invention describes a novel approach based on a co-culture that addresses this problem.
This invention describes a method of splitting the biosynthetic pathway for an isoprenoid between two cells, which together make up a co-culture capable of synthesizing isoprenoids from simple carbon sources. In principle, the method can be applied to any isoprenoid with a membrane-permeable metabolic intermediate.
The Inventors have successfully demonstrated this technique as applied to the biosynthesis of an oxygenated taxane (a paclitaxel precursor). In this instance, the co-culture is made up of an E. coli strain engineered to express the biosynthetic pathway needed to produce taxadiene from xylose and an S. cerevisiae strain expressing the yew cytochrome P450 (CYP) required to catalyze the conversion of taxadiene to an oxygenated taxane. A co-culture of these two strains in a fed-batch bioreactor was able to synthesize oxygenated taxanes with a yield of 35 mg/L.
In addition to reducing the cellular stress experienced by each recombinant strain, using a co-culture also enables an additional mode of process control by altering the ratio of the two strains. In this case, the concentration of ethanol was used to manipulate the cell population ratio since it is a carbon source used exclusively by S. cerevisiae.
Allows biosynthesis of isoprenoids with complex biosynthetic pathways by reducing protein expression load experienced by each cell
- Affords additional method of process control by varying cell population ratio