Assessing Aspergillus oryzae as a Fungal Chassis for Cyanobacterial Biosynthetic Gene Clusters via Heterologous Expression of the Lyngbyatoxin Biosynthetic Pathway

Cyanobacterial biosynthetic gene clusters (BGCs) remain difficult to reconstruct in heterologous systems, yet the suitability of fungal hosts for expression of cyanobacterial pathways remains largely unexplored. Here, the well-characterized lyngbyatoxin A (LTXA) biosynthetic gene cluster was used as a model system to evaluate the capacity of Aspergillus oryzae to support cyanobacterial NRPS biosynthesis. The lyngbyatoxin biosynthetic genes (ltxA, ltxB, and ltxC) were individually cloned and expressed in Aspergillus oryzae NSAR1 under the control of an inducible promoter. Metabolite production was assessed by LCMS, while transcriptional analysis was performed using RT-PCR. Codon-optimized constructs and precursor feeding experiments were used to evaluate pathway functionality. No detectable production of LTXA or pathway intermediates was observed following co-expression of ltxA–C despite confirmed transcription of ltxB and ltxC. RT-PCR analysis could not reliably detect ltxA transcripts for unknown reasons. In contrast, expression of a codon-optimized ltxC enabled biotransformation of indolactam V to LTXA in A. oryzae, confirming functional expression of the prenyltransferase. Overall, this work establishes lyngbyatoxin biosynthesis as a useful model system for evaluating fungal chassis compatibility with cyanobacterial BGCs and provides insights for future engineering of fungal platforms for natural product biosynthesis.