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

For decades micoorganisms have been engineered for the utilization of lignocellulose-based second-generation (2G) feedstocks, but with the concerns of increased levels of atmospheric CO₂ causing global warming there is an emergent need to transition from the utilization of 2G feedstocks to third-generation (3G) feedstocks such as CO₂ and its derivatives. Here, we established a yeast platform that is capable of simultaneously converting 2G and 3G feedstocks into bulk and value-added chemicals. We demonstrated that by adopting 3G substrates such as CO₂ and formate, the conversion of 2G feedstocks could be substantially improved. Specifically, formate could provide reducing power and energy for xylose conversion into valuable chemicals. Simultaneously, it can form a concentrated CO₂ pool inside the cell, providing thermodynamically and kinetically favoured amounts of precursors for CO₂ 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. The engineered strain achieved a one-carbon (C1) assimilation efficiency of 9.2%, which was the highest efficiency observed in the co-utilization of 2G 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 co-utilization of 2G and 3G feedstocks sheds lights on both basic and applied research for the up-coming establishment of 3G biorefineries.