초록
<P><B>Background</B></P><P>Geraniol is an acyclic monoterpene alcohol, which exhibits good prospect as a gasoline alternative. Geraniol is naturally encountered in plants at low concentrations and an attractive target for microbial engineering. Geraniol has been heterologously produced in <I>Escherichia coli</I>, but the low titer hinders its industrial applications. Moreover, bioconversion of geraniol by <I>E. coli</I> remains largely unknown.</P><P><B>Results</B></P><P>Recombinant overexpression of <I>Ocimum basilicum</I> geraniol synthase, <I>Abies grandis</I> geranyl diphosphate synthase, and a heterotic mevalonate pathway in <I>E. coli</I> BL21 (DE3) enabled the production of up to 68.6 ± 3 mg/L geraniol in shake flasks. Initial fed-batch fermentation only increased geraniol production to 78.8 mg/L. To further improve the production yield, the fermentation conditions were optimized. Firstly, 81.4 % of volatile geraniol was lost during the first 5 h of fermentation in a solvent-free system. Hence, isopropyl myristate was added to the culture medium to form an aqueous-organic two-phase culture system, which effectively prevented volatilization of geraniol. Secondly, most of geraniol was eventually biotransformed into geranyl acetate by <I>E. coli</I>, thus decreasing geraniol production. For the first time, we revealed the role of acetylesterase (Aes, EC 3.1.1.6) from <I>E. coli</I> in hydrolyzing geranyl acetate to geraniol, and production of geraniol was successfully increased to 2.0 g/L under controlled fermentation conditions.</P><P><B>Conclusions</B></P><P>An efficient geraniol production platform was established by overexpressing several key pathway proteins in engineered <I>E. coli</I> strain combined with a controlled fermentation system. About 2.0 g/L geraniol was obtained using our controllable aqueous-organic two-phase fermentation system, which is the highest yield to date. In addition, the interconversion between geraniol and geranyl acetate by <I>E. coli</I> was first elucidated. This study provided a new and promising strategy for geraniol biosynthesis, which laid a basis for large-scale industrial application.</P>