Sulfur assimilation determines S-adenosyl-l-methionine flux for enhancing methylation efficiency in heterologous biosynthesis

S-adenosyl-l-methionine (SAM) is not only crucial for cellular physiological processes as a methyl donor and signaling molecule but also a methyl donor for heterologous biosynthesis. Efforts for increasing SAM availability have focused primarily on improving the efficiency of C1 cycle (SAM cycle), while the total flux of SAM has been largely overlooked. Here, we found that sulfur assimilation-specifically, the first reduction step of sulfate catalyzed by MET3, MET14, and MET16-has a determined impact on SAM flux compared with C4 skeleton (activated form of l-homoserine) biosynthesis. These three genes increased the SAM level and further significantly increased the methylation rate of two methylated compounds, bikaverin and ferulic acid. Their titers increased significantly in the overproducing strains, achieving 361.4 ± 8.6 and 552.1 ± 5.4 mg/l, respectively. These findings redefine sulfur assimilation as a key point in SAM metabolism and establish a new paradigm for the enhancement of SAM flux, and they also provide an engineering strategy for optimizing the production of SAM-dependent natural products.