Plasmid pSNA-MrBBS contained IPTG-inducible lac and trc promoters for expression of the complete MVA pathway genes and MrBBS gene, respectively (Fig. 1b). To ascertain the optimal inducer concentration for (−)-α-bisabolol production in E. coli DH5α with pSNA-MrBBS, induction was conducted with varying concentrations of IPTG ranging from 0 to 0.1 mM. Interestingly, leaky expression of the MrBBS and MVA pathway genes in the absence of IPTG showed the highest production of (−)-α-bisabolol (38.9 mg/L). At all other IPTG concentrations (−)-α-bisabolol production decreased as the IPTG concentration increased (Fig. 5b) whereas the growth of E. coli DH5α cells is similar regardless of IPTG concentration (Additional file 1: Figure S3B). This result is compatible with a previous report  that showed lycopene production in E. coli expressing lower MVA pathway genes regulated by the trc promoter decreased under all IPTG-induced conditions. In addition, constitutive promoters controlling the expression of MVA pathway genes showed much lower production of amorphadiene than that from IPTG-inducible lacUV5 and trc promoters . High expression of the MVA pathway and MrBBS genes under IPTG induced conditions could cause a deficiency of FPP for essential cellular metabolism. Furthermore, the accumulation of toxic intermediates of the MVA pathway, including IPP and 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) [32, 35], could cause growth inhibition along with a decrease of (−)-α-bisabolol production. In addition, we investigated the effects of initial pH of the cultivation of E. coli DH5α with pSNA-MrBBS on the production of (−)-α-bisabolol. The optimal pH for (−)-α-bisabolol production was pH 7 (38.2 mg/L, Fig. 5c). To determine the ideal E. coli strains for (−)-α-bisabolol production under the optimized culture conditions, we individually introduced the plasmid pSNA-MrBBS into three different E. coli strains (DH5α, MG1655, or BL21(DE3)) and measured the (−)-α-bisabolol concentration produced from each. E. coli DH5α cells produced the highest amount of (−)-α-bisabolol, and BL21(DE3) showed an approximate 13-fold decrease in (−)-α-bisabolol production compared to DH5α (38.4 mg/L, Fig. 5d). We also measured cell growth during examination of pH effects on (−)-α-bisabolol production in E. coli DH5α expressing MrBBS and entire MVA pathway genes. Although cell growth slightly decreased at a pH 5 or 6, it was similar at all other pHs (Additional file 1: Figure S3C).