The transition from 2G to 3G-feedstocks enabled efficient production of fuelsand chemicals

For decades micoorganisms have been engineered for the utilization of lignocellulose-based second-generation (2G) feedstocks, but with theconcerns of increased levels of atmospheric CO_(2) causing global warming there is an emergent need to transition from the utilization of 2Gfeedstocks to third-generation (3G) feedstocks such as CO_(2) and its derivatives. Here, we established a yeast platform that is capable ofsimultaneously converting 2G and 3G feedstocks into bulk and value-added chemicals. We demonstrated that by adopting 3G substrates such asCO_(2) and formate, the conversion of 2G feedstocks could be substantially improved. Specifically, formate could provide reducing power andenergy for xylose conversion into valuable chemicals. Simultaneously, it can form a concentrated CO_(2) pool inside the cell, providing thermodynamically and kinetically favoured amounts of precursors for CO_(2) fixation pathways, e.g., the Calvin–Benson–Bassham (CBB) cycle.Furthermore, we demonstrated that formate could directly be utilized as a carbon source by yeast to synthesize endogenous amino acids. Theengineered strain achieved a one-carbon (C1) assimilation efficiency of 9.2%, which was the highest efficiency observed in the co-utilization of2G and 3G feedstocks. We applied this strategy for productions of both bulk and value-added chemicals, including ethanol, free fatty acids(FFAs), and longifolene, resulting in yield enhancements of 18.4%, 49.0%, and ~100%, respectively. The strategy demonstrated here for coutilization of 2G and 3G feedstocks sheds lights on both basic and applied research for the up-coming establishment of 3G biorefineries.