Investigating Fungal Biosynthetic Pathways Using Heterologous Gene Expression: Aspergillus oryzae as a Heterologous Host

Divergent Biosynthesis of Bridged Polycyclic Sesquiterpenoids by a Minimal Fungal Biosynthetic Gene Cluster

The bridged polycyclic sesquiterpenoids derived from sativene, isosativene, and longifolene have unique structures, and many chemical synthesis approaches with at least 10 steps have been reported. However, their biosynthetic pathway remains undescribed. A minimal biosynthetic gene cluster (BGC), named bip, encoding a sesquiterpene cyclase (BipA) and a cytochrome P450 (BipB) is characterized to produce such complex sesquiterpenoids with multiple carbon skeletons based on enzymatic assays, heterologous expression, and precursor experiments. BipA is demonstrated as a versatile cyclase with (-)-sativene as the dominant product and (-)-isosativene and (-)-longifolene as minor ones. BipB is capable of hydroxylating different enantiomeric sesquiterpenes, such as (-)-longifolene and (+)-longifolene, at C-15 and C-14 in turn. The C-15- or both C-15- and C-14-hydroxylated products are then further oxidized by unclustered oxidases, resulting in a structurally diverse array of sesquiterpenoids. Bioinformatic analysis reveals the BipB homologues as a discrete clade of fungal sesquiterpene P450s. These findings elucidate the concise and divergent biosynthesis of such intricate bridged polycyclic sesquiterpenoids, offer valuable biocatalysts for biotransformation, and highlight the distinct biosynthetic strategy employed by nature compared to chemical synthesis.

Synthetic Biology Tools for Engineering Aspergillus oryzae

For more than a thousand years, Aspergillus oryzae has been used in traditional culinary industries, including for food fermentation, brewing, and flavoring. In recent years, A. oryzae has been extensively used in deciphering the pathways of natural product synthesis and value-added compound bioproduction. Moreover, it is increasingly being used in modern biotechnology industries, such as for the production of enzymes and recombinant proteins. The investigation of A. oryzae has been significantly accelerated through the successive application of a diverse array of synthetic biology techniques and methodologies. In this review, the advancements in biological tools for the synthesis of A. oryzae, including DNA assembly technologies, gene expression regulatory elements, and genome editing systems, are discussed. Additionally, the challenges associated with the heterologous expression of A. oryzae are addressed.