Reprogramming yeast metabolism for customized starch-rich micro-grain through low-carbon microbial manufacturing

Starch is a primary food ingredient and bulk industrial feedstock. Producing starch through fermentation-based low-carbon microbial manufacturing serves as an arable land-independent and carbon-neutral/negative approach, while the efficiency of this route is highly dependent on the starch producer. We reconfigure the oleaginous yeast as an efficient cell factory for starch-rich micro-grain production by rewiring the starch biosynthesis and gluconeogenesis pathways and regulating cell morphology. With the CO2 electro-synthesized acetate as the substrate, the strain accumulates starch up to 47.18% of the dry cell weight. Through the cultivation of the micro-grain in fed-batch bioreactors, starch was produced at 19.30 g/L, 29.60% starch content, and spatial-temporal productivity (243.7 g/m2/d), approximately 50-fold higher than that of crop cultivation and an order of magnitude higher rate (160.83 mg/L/h) than the starch production in other microbes. We validated that the starch composition and starch-protein ratio in the micro-grain can be modulated by strain and process engineering. More surprisingly, we found that the engineered artificial strains adopted a cellular resources reallocation strategy to ensure high-level starch production in micro-grain, and could facilitate a highly efficient straw/cellulose-to-starch conversion. Our work lays the foundation for understanding the global cellular machinery for starch biosynthesis and enables a superior-to-nature high-level production of starch with customized composition, aiding the development of efficient and low-carbon production of nutritional resources.