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

## TL;DR

Scientists identified a gene cluster in a fungus that produces a blue-green pigment called xylindein, which could be useful for textiles and semiconductors.

## Contribution

The study identifies a biosynthetic gene cluster for xylindein production in Chlorociboria fungi and explores heterologous expression in Aspergillus oryzae.

## Key findings

- A unique biosynthetic gene cluster containing a nonreducing polyketide synthase (nrPKS) was identified in Chlorociboria fungi.
- RNA sequencing showed that the core gene XLNpks is co-regulated with eight other genes during xylindein production.
- Heterologous expression of the related viriditoxin nrPKS in Aspergillus oryzae produced an expected intermediate, but not for xylindein.

## Abstract

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.