Hao Luo

Abstract Acetyl-CoA is a fundamental metabolite for all life on Earth, and is also a key starting point for the biosynthesis of a variety of industrial chemicals and natural products. Here we design and construct a Synthetic Acetyl-CoA (SACA) pathway by repurposing glycolaldehyde synthase and acetyl-phosphate synthase. First, we design and engineer glycolaldehyde synthase to improve catalytic activity more than 70-fold, to condense two molecules of formaldehyde into one glycolaldehyde. Second, we repurpose a phosphoketolase to convert glycolaldehyde into acetyl-phosphate. We demonstrated the feasibility of the SACA pathway in vitro, achieving a carbon yield ~50%, and confirmed the SACA pathway by 13 C-labeled metabolites. Finally, the SACA pathway was verified by cell growth using glycolaldehyde, formaldehyde and methanol as supplemental carbon source. The SACA pathway is proved to be the shortest, ATP-independent, carbon-conserving and oxygen-insensitive pathway for acetyl-CoA biosynthesis, opening possibilities for producing acetyl-CoA-derived chemicals from one-carbon resources in the future.

Lignin as a polymer of monomeric aromatic compounds retains great potential to be a source for liquid fuels and valuable chemicals. However, lignin from biomass has been traditionally treated as a waste byproduct and in most applications burned for its heat value. In this work, we report the catalytic conversion of lignin in Miscanthus into aromatic products by using earth-abundant Ni catalyst supported on activated carbon, under relatively mild conditions. The special ferulate linkage in grasses gives methyl ferulate ester and its derivatives, which were not observed for wood biomass substrates. By modification of the reaction conditions, saturated or unsaturated branched products can be obtained selectively. Optimal conditions give over 68% yield of select aromatic products from lignin. Furthermore, after lignin depolymerization and upgrading, the carbohydrates of miscanthus were recovered as a solid residue, which upon treatment with iron chloride produced useful platform chemicals (furfurals and levulinic acid). On the basis of our study, all three major components of biomass (lignin, cellulose and hemicellulose) are effectively utilized, with an overall 55% conversion of total accessible biomass into high value chemicals with 98% mass balance.

Biomass pretreatment methods are commonly used to isolate carbohydrates from biomass, but they often lead to modification, degradation, and/or low yields of lignin. Catalytic fractionation approaches provide a possible solution to these challenges by separating the polymeric sugar and lignin fractions in the presence of a catalyst that promotes cleavage of the lignin into aromatic monomers. Here, we demonstrate an oxidative fractionation method conducted in the presence of a heterogeneous non-precious-metal Co-N-C catalyst and O2 in acetone as the solvent. The process affords a 15 wt% yield of phenolic products bearing aldehydes (vanillin, syringaldehyde) and carboxylic acids (p-hydroxybenzoic acid, vanillic acid, syringic acid), complementing the alkylated phenols obtained from existing reductive catalytic fractionation methods. The oxygenated aromatics derived from this process have appealing features for use in polymer synthesis and/or biological funneling to value-added products, and the non-alkaline conditions associated with this process support preservation of the cellulose, which remains insoluble at reaction conditions and is recovered as a solid.