New application of Aspergillus versicolor in promoting plant growth after suppressing sterigmatocystin production via genome mining and engineering

Abstract

Aspergillus genus is a key component in fermentation and food processing. However, sterigmatocystin (STE)-a mycotoxin produced by several species of Aspergillus-limits the use of some Aspergillus species (such as Aspergillus versicolor, Aspergillus inflatus, and Aspergillus parasiticus) because of its toxicity and carcinogenicity. Here, we engineered an STE-free Aspergillus versicolor strain based on genome mining techniques. We sequenced and assembled the Aspergillus versicolor D5 genome (34.52 Mb), in which we identified 16 scaffolds and 54 biosynthetic gene clusters (BGCs). We silenced cytochrome P450 coding genes STC17 and STC27 by insertional inactivation. The production of STE in the Δstc17 mutant strain was increased by 282% but no STE was detected in the Δstc27 mutant. Metabolites of Δstc27 mutant exhibited growth-promoting effect on plants. Our study makes significant progress in improving the application of some Aspergillus strains by restricting their production of toxic and carcinogenic compounds.

FIGURE 1

Genome analysis of Aspergillus versicolor D5. (A) Assembly of Aspergillus versicolor D5 genome. From the inside out, circle 1 showed the scaffolds of D5 genome, circle 2–4 showed all genes position, circle 5 showed the position of different types BCGs. (B) KEGG analysis of predicted genes in Aspergillus versicolor D5 genome.

FIGURE 2

Phylogenetic tree of Aspergillus versicolor D5 and other related Aspergillus genera in MycoCosm.

FIGURE 3

Analysis and modification of STE‐related gene cluster in Aspergillus versicolor D5. (A) Predicted genes in STE‐related gene cluster. (B) Heatmap of expression levels of the genes in STE‐related gene cluster. (C) HPLC analysis of the fermentation products produced by mutant strains and wild strains. STE, STE reference standard; D5, wild strain; Δstc17‐1 and Δstc27‐4, the mutant strain that silenced STC17 and STC27 respectively.

FIGURE 4

Analysis of the activity of STE‐free strain products on plant growth. Error bars indicate SD (n = 36); the statistical significance was determined by Student's t‐test (*p < 0.05, two‐sided). (A) Amaranthus retroflexus L; (B) Nicotiana tabacum; (C) Glycine max.