## 4 Common Strategies for Optimizing Sesquietpenol Biosynthesis
### The Strategies for the Regulation of the Synthesis Pathway
#### 4.2.2 The Enhancement of the Central Carbon Flux  
Within complex metabolic networks, multiple biosynthetic pathways coexist, often depleting central carbon flux and leading to by-product accumulation. Acetyl-CoA, a key metabolic intermediate in cellular processes, is essential for producing biotransformation-derived bio-based chemicals, and serves as a central node in microbial carbon metabolism. In yeasts, where sesquiterpenol biosynthesis primarily relies on the cytosolic acetyl-CoA pool as the starting substrate for the MVA pathway, enhancing acetyl-CoA availability is a strategic approach to improve production (Figure 5b, Table 2). Acetyl-CoA primarily originates from two sources: mitochondrial generation via ATP-citrate lyase in the TCA cycle and the cytoplasmic pyruvate dehydrogenase (PDH) bypass pathway [117]. Current enhancement strategies mainly focus on overexpressing ATP-citrate lyase (ACL) and optimizing the PDH bypass. In squalene-producing systems, heterologous expression of _Salmonella enterica_ acetyl-CoA synthase (acs*) and endogenous yIACL1 increased cytosolic acetyl-CoA levels by over 50% [118]. [PERSON] et al. used a strong promoter to overexpress ADH2 and ACS2, which encode acetyl-CoA synthase in _S. cerevisiae_. This enhanced the PDH bypass and endogenous acetyl-CoA flux, boosting patchouloid production by 1.34-fold to 151.27 \(\pm\) 4.77 mg/L [76]. The peroxisomal \(\beta\)-oxidation pathway also significantly contributes to the acetyl-CoA pool. [PERSON] et al. optimized this pathway in \(\alpha\)-bisabolol-producing strains by balancing acetyl-CoA partitioning between endogenous lipid metabolism and heterologous biosynthesis, achieving 364.23 mg/L \(\alpha\)-bisabolol production [70]. Recent advancements include the development of synthetic acetyl-CoA (SACA) pathways. These artificial biosynthetic pathways enable acetyl-CoA synthesis from formaldehyde through three enzymatic steps. This is the first engineered acetyl-CoA pathway and the shortest known biosynthetic route to acetyl-CoA, offering promising applications for sesquiterpenol bioproduction [119]. Collectively, these efforts demonstrate that strategically enhancing acetyl-CoA supply is an effective approach to improving sesquiterpenol biosynthesis efficiency.  
Enhancing acetyl-CoA supply can boost central carbon flux and target compound biosynthesis. However, static methods often disrupt cellular homeostasis and fail to achieve central carbon flux distribution between cell growth and product synthesis. Recent advances in synthetic biology are driving the development of increasingly sophisticated dynamic regulation strategies [120]. Emerging solutions integrate biosensors [121] and genetic circuits for real-time flux control, coupled with genome-scale metabolic models (GEMs) [122] for in silico pathway optimization through computational simulations and mathematical modeling. These intelligent systems dynamically coordinate cellular growth phases with production stages, facilitating adaptive resource allocation. This technological convergence between dynamic regulation and predictive modeling is poised to revolutionize terpenoid biomanufacturing. It offers unparalleled metabolic engineering precision and enhances the fundamental capabilities of synthetic biology platforms.