Whole-cell biocatalysis of HMF into BHMF by Aspergillus niger: Process development and identification of key genes

The conversion of 5-hydroxymethylfurfural (HMF), a key platform chemical derived from lignocellulosic biomass, into value-added products such as 2,5-bis(hydroxymethyl)furan (BHMF) is of great interest for sustainable biorefineries. In this study, a whole-cell biocatalytic system using Aspergillus niger M13 was developed for the selective reduction of HMF to BHMF. Through systematic optimization, a minimal reaction medium composed solely of sterile water and glucose was developed. The highest catalytic activity was obtained with cells harvested after 72 h of cultivation and used at a concentration of 120 mg/mL, resulting in 100% HMF conversion and a BHMF yield of 84.1% within 12 h. Fed-batch and sequential-batch strategies enabled sustained BHMF production, with the cells being reused for 21 cycles in repeated-batch mode at an average BHMF yield of 76.8%. Furthermore, regeneration of inactivated cells extended the catalytic lifespan by 43%. Transcriptomic analysis under HMF stress revealed several significantly upregulated oxidoreductase genes, including alcohol dehydrogenases and aldehyde dehydrogenases, providing genetic targets for future strain engineering. The A. niger M13-based system operates under mild conditions, requires simple components, and aligns with green chemistry principles, offering an efficient and sustainable biocatalytic platform for upgrading biomass-derived HMF into valuable furan chemicals.