Metabolic engineering of Bacillus subtilis for terpenoids production

Terpenoids represent a large collection of naturally produced chemicals of which many play an important role to produce pharmaceuticals. The antimalarial drug artemisinin and the chemotherapeutic agent paclitaxel (Taxol®) are outspoken representatives of this class of natural products. In order to establish a stable and efficient “cell factory” for the production of terpenoids, the potential of using Bacillus subtilis as a host was researched in this thesis. The effect of systematic overexpression of the genes involved in the methylerythritol phosphate (MEP) pathway, which upregulates the building block for terpenoid compounds, isoprene, was investigated in B. subtilis. It was shown that the production of carotenoids, a C30 terpenoid, can be increased significantly by overexpressing the MEP pathway enzymes. Then, the segregational and structural stability of the B. subtilis host overexpressing the MEP pathway enzymes were further evaluated. A strain overexpressing eight genes of the MEP pathway on a plasmid clearly produced the highest level of C30 carotenoids. The level of transcription for each gene in the operon was analyzed by RT-qPCR analysis. This is the first report of merging and stably expressing this large size operon (complete MEP pathway) from a plasmid-based system in B. subtilis. Moreover, this study demonstrates the possibility to express the terpene cyclase, amorphadiene synthase (ADS), in B. subtilis in combination with overexpression of MEP pathway enzymes leading to the production of a considerable yield of amorphadiene.