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.

Investigating formate tolerance mechanisms in Saccharomyces cerevisiae and its application

Current global energy and environmental crisis have spurred efforts towards developing sustainable biotechnological solutions,such as utilizing CO_(2) and its derivatives as raw materials.Formate is an attractive onecarbon source due to its high solubility and low reduction potential.However,the regulatory mechanism of formate metabolism in yeast remains largely unexplored.This study employed adaptive laboratory evolution(ALE)to improve formate tolerance in Saccharomyces cerevisiae and characterized the underlying molecular mechanisms.The evolved strain was applied to produce free fatty acids(FFAs)under high concentration of formate with glucose addition.The results showed that the evolved strain achieved a FFAs titer of 250 mg/L.Overall,this study sheds light on the regulatory mechanism of formate tolerance and provides a platform for future studies under high concentrations of formate.