# Biosynthesis Progress of High-Energy-Density Liquid Fuels Derived from Terpenes
## 3 Microbial Synthesis of Monoterpene and Sesquiterpene Fuels
### Microbial Synthesis of Sesquiterpenes
The above description shows that remarkable progress has been made in the production of terpene fuels through microbial fermentation using glucose, sucrose or glycerol as the carbon source (Table 2). By using a chassis that can efficiently utilize other types of carbon sources, such as _R. toruloides_[50], _Trichoderma atroviride_[62] and endophytic fungus _Annulophyoxylon_[63], terpene fuels can be produced from non-food biomass like cellulose. Additionally, algae, with their photosynthetic ability and faster growth compared to plants, have gained more attention regarding terpene fuel production [64]. Algae can also grow and reproduce in wastewater or seawater, effectively utilizing nitrogen and phosphorus sources in wastewater, leading to potential applications in bioremediation and reducing freshwater dependency during fermentation [65; 66]. [PERSON] et al. achieved the efficient synthesis of monocyclic limonene in cyanobacteria by regulating the expression of GPP synthase and other synthases involving the MEP pathway, resulting in a limonene titer of 16.4 mg/L after two days of cultivation [67]. However, the production of pineinee in algae is significantly lower compared to limonene. [PERSON] et al. and [PERSON] et al. separately synthesized pinee in _Synechocystis_ sp. PCC 6803, achieving a titer of 40 ug/L at 168 h and 80 ug/L at 21 days, respectively [46; 68]. Researchers have also achieved the synthesis of sesquiterpene in algae. [PERSON] et al. achieved the synthesis of \(\beta\)-caryophyllene by constructing the \(\beta\)-caryophyllene synthetic pathway and enhancing the precursor supply in _Synechocystis_ UTEX 2973, and the production of \(\beta\)-caryophyllene in a photobioreactor reached 212.37 ug/L with high-density cultivation [69]. These studies have laid a solid foundation for the future synthesis of HED fuels using non-food biomass. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Product** & **Chassis** & **Synthetase** & **Conditions** & **Carbon Source** & **Production** & **Ref.** \\ \hline \multicolumn{6}{c}{**Monoterpene**} \\ \hline Limonene & _E. coli_ BL21 (DE3) & Limonene synthase from _Mentha spicata_ & Fed-batch fermentation/3.1 L & Glycerol & 24 h, 3.63 g/L & [45] \\ \hline \multirow{4}{*}{\(\alpha\)-Pinene} & _E. coli_ BW25113 & PS from _Pinus tada_ & Whole-cell biocatalysis/50 mL & Glucose & 28 h, 166.50 mg/L & [47] \\ \cline{2-6}  & _E. coli_ MG1655 & PS from _Abies grandis_ & Shake-flask fermentation/10 mL & Glucose & 48 h, 165.10 mg/L & [48] \\ \hline \multirow{2}{*}{Sabinene} & _E. coli_ BL21(DE3) & SabS1 from _Salvia pomifera_ & Fed-batch fermentation/5 L & Glycerol & 24 h, 2.65 g/L & [49] \\ \cline{1-1} \cline{2-6}  & & & & & \\ \end{tabular}
\end{table} 
Table 2: Summary of microbial synthesis of monoterenes and sesquiterpenes. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Product** & **Chassis** & **Synthetase** & **Conditions** & **Carbon Source** & **Production** & **Ref. ** \\ \hline Myrcene & _E. coli_ MG1655 & \begin{tabular}{c} CsMS from \\ _Camabis sativa_ \\ \end{tabular}  & \begin{tabular}{c} Shake-flask \\ fermentation/10 mL \\ \end{tabular}  & Glucose & 72 h, 510.38 mg/L & [70] \\ \hline \(\gamma\)-Terpinene & _E. coli_ BL21 (DE3) & \ \begin{tabular}{c} \(\gamma\)-Terpinene \\ synthesase _Tymus_ \\ _cularis_ \\ \end{tabular}  & \begin{tabular}{c} Fed-batch \\ fermentation/2 L \\ \end{tabular}  & Glycerol & 72 h, 275.41 mg/L & [71] \\ \hline