Modular Pathway Optimization for Production n-Butanol from Red Seaweed in Escherichia coli

Marine biomass, known as the third generation of biomass, has many advantages rather than conventional biomass due to its high biomass productivity, carbon fixation rate, and easy pretreatment process, etc. Especially, red seaweed which is mainly cultivated in Asia, contains galactose and glucose, many bio-chemicals can be produced from these sugars through fermentation process. However, the challenging problem is that galactose is not favored by many industrial microorganisms (for example, Escherichia coli). Slow utilization rate and carbon catabolite repression limits carbon flux and results in low productivity and titer. In this research, we introduced two synthetic modules to utilize sugars from hydrolysate of red seaweed (Gelidium amansii) and to produce n-butanol, one of advanced fuel. The modules with metabolic enzymes under synthetic promoters, rationally designed 5’UTRs (5’untranslated region), and terminators for maximum catalytic activity were assembled, and these modules were optimized by finding maximum productivity with various expression of specific gene. With this approach, the engineered strain showed significantly enhanced sugar utilization and n-butanol production from both red seaweed mimetic media and real hydrolysate. Finally, we could confirm the possibility of marine biomass as carbon source to produce many valuable bio-products instead of fossil fuel.