Identification of a Biosynthetic Gene Cluster for the Production of the Blue-Green Pigment Xylindein by the Fungus Chlorociboria aeruginascens.

Xylindein is a blue-green pigment produced by the fungi Chlorociboria aeruginascens and Chlorociboria aeruginosa. Its stunning color and optoelectronic properties make xylindein valuable for textiles and as a natural semiconductor material. However, producing xylindein from culture broths remains challenging because of the slow growth of the Chlorociboria species and the poor solubility of xylindein in organic solvents. An alternative production route for obtaining pure xylindein is heterologous expression of the xylindein biosynthetic genes. Here, we resequenced the genome of C. aeruginascens and C. aeruginosa, and subsequent genome mining and phylogenetic dereplication identified a unique candidate biosynthetic gene cluster with a nonreducing polyketide synthase (nrPKS). RNA sequencing during xylindein production revealed that the core gene XLNpks is co-regulated with eight other genes at the locus. Among those, XLNfas1 and XLNfas2 encode a putative fatty acid synthase, which likely provides the starter unit to XLNpks. Attempts to heterologously express in Aspergillus oryzae XLNpks alone or in combination with XLNfas1 and XLNfas2 did not yield any intermediate, but expression of the closely related viriditoxin nrPKS (VdtA) produced the expected intermediate. Based on our results, we propose a biosynthetic route to xylindein and suggest that the obtained A. oryzae transformants open ways to further study xylindein biosynthesis.