De novo biosynthesis and gram-level production of m-cresol in Aspergillus nidulans

The industrially important meta -cresol ( m -cresol, 3-methylphenol) is mainly produced from fossil resources by chemical methods. The microbial production of m -cresol was rarely investigated. Herein, we constructed a platform for the overproduction of m -cresol in a modified fungus Aspergillus nidulans FGSC no. A1145 ∆ST∆EM , which gave a gram-level titer using starch as carbon resource. For the biosynthesis of m -cresol, the 6-methyl salicylic acid synthase (MSAS)-encoding gene patK and 6-methyl salicylic acid decarboxylase-encoding gene patG from A. clavatus were co-expressed in the host A. nidulans . Multiple strategies, including promotor engineering, gene multiplication, and fed-batch fermentation, were applied to raise the production of m -cresol, which resulted in the titers of 1.29 g/L in shaking flasks and 2.03 g/L in fed-batch culture. The chassis cell A. nidulans A1145 ∆ST∆EM was proved to possess better tolerance to m -cresol than yeast, as it could grow in the liquid medium containing up to 2.5 g/L of m -cresol. These results showed that A. nidulans has great potential to be further engineered for industrial production of m -cresol. Key points • m-Cresol was de novo biosynthesized by a fungal chassis cell Aspergillus nidulans. • Promoter engineering and gene multiplication implemented the fine-tuned genes expression. • The titer of m-cresol reached 2.03 g/L via fed-batch culture. Graphical abstract