Geranyl diphosphate synthase: an important regulation point in balancing a recombinant monoterpene pathway in Escherichia coli.

The expression level of geranyl diphosphate synthase (GPPS) was suspected to play a key role for geraniol production in recombinant Escherichia coli harboring an entire mevalonate pathway operon and a geraniol synthesis operon. The expression of GPPS was optimized by using ribosomal binding sites (RBSs) designed to have different translation initiation rates (TIRs). The RBS strength in TIR window of 500 arbitrary unit (au)-1400 au for GPPS appears to be suitable for balancing the geraniol biosynthesis pathway in this study. With the TIR of 500 au, the highest production titer of geraniol was obtained at a level of 1119mg/L, which represented a 6-fold increase in comparison with the previous titer of 183mg/L. The TIRs of GPPS locating out of range of the optimal window (500-1400 au) caused significant decreases of cell growth and geraniol production. It was suspected to result from metabolic imbalance and plasmid instability in geraniol production by inappropriate expression level of GPP synthase. Our results collectively indicated GPPS as an important regulation point in balancing a recombinant geraniol synthesis pathway. The GPPS-based regulation approach could be applicable for optimizing microbial production of other monoterpenes.