A solvent-tolerant whole-cell biocatalyst for chemoselective oxidation of aldehydes to carboxylic acids

The conversion of aldehydes into carboxylic acids through biocatalysis is a promising approach in the fields of green organic synthesis and biotechnology. In this work, we have developed a biocatalytic method for the oxidation of aldehydes to form carboxylic acid in the aqueous phase by using a newly discovered whole D. xibeiensis R13 cell biocatalyst. The whole-cell biocatalyst exhibited excellent organic solvent tolerance and a low biocatalyst/substrate ratio in the selective oxidation of biomass-derived furfural to 2­furoic acid. Under optimal conditions, a yield of 93 % was achieved after 12 h with a conversion of 250 mM furfural substrate. The microbial oxidation of furfural was further scaled up by a fed-batch strategy, with a productivity of 1.3 g/L per hour and a total yield of 83 %. A panel of aldehydes with various reactive moieties was efficiently converted with expected carboxylic acids as the sole product under mild reaction conditions, indicating excellent chemoselectivity (>99 %) and wide substrate scope. The new biocatalytic method avoids the use of toxic transition-metal reagents, representing a green and sustainable alternative to chemical methods.