Biotransformation of terpenes by Polyporus brumalis and investigation of related enzyme expression by transcriptome analysis

Abstract

In this study, the biotransformation of the monoterpenes, α-pinene and geraniol, was performed to synthesize valuable compounds. Polyporus brumalis, which is classified as a white rot fungus, was used as a biocatalyst. As the results, α-terpineol, borneol, and fenchol were transformed from α-pinene by P. brumalis. Additionally, the biocatalyst transformed acyclic geraniol to cyclic compounds, such as isopulegol and p-menthane-3,8-diol. The main transformation products, α-terpineol and p-menthane-3,8-diol, are known to be bioactive monoterpenoids. In addition, P. brumalis catalyzed the de-novo synthesis of sesquiterpenoids such as β-eudesmol and elemol, in the absence of specific substrates. The β-eudesmol produced from the P. brumalis has a eudesmane skeleton, which is a difficult target for chemical synthesis. These results indicated the presence of terpene metabolism on mycelium of P. brumalis. This hypothesis was demonstrated via next-generation sequencing of the transcriptome of P. brumalis mycelium. NGS (next generation sequencing) technology provided evidence of catalytic function of P. brumalis in the biotransformation through the prediction of encoded enzymes based on the expressed transcriptomes. Through the Illumina HiSeq TM 2000 sequencing platform, high-quality reads were assembled to yield 23,876 unigenes from P. brumalis. The unigenes were aligned using the NCBR NR database and automatically assigned gene functions based on the corresponding GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway. Terpene metabolism such as monoterpene synthesis, pinene and limonene degradation, sesquiterpene and triterpene synthesis and terpene backbone biosynthesis are related in mycelium of P. brumalis. Especially, two different terpenoid synthesis pathways, the MEA (mevalonic acid) and MEP (2-methyl-D-erythritol-4-phosphate) pathway were expressed in the terpene backbone biosynthesis. The expressions of the MEA and MEP pathways support the biosynthesis of the sesquiterpenoids from the P. brumalis. Thus, the investigation of the pathway of terpene backbone biosynthesis may provide an important means to understand terpene biosynthesis in basidiomycetes. In conclusion, this study demonstrated the chemical modification of terpene compounds and their de novo synthesis by P. brumalis based on the genes identified through a transcriptome analysis.