2022 Volume 72 Issue 2 Pages 75-83
The fungal strains belonging to Aspergillus section Nigri such as A. niger and A. tubingensis are industrially important microorganisms. However, some of Aspergillus section Nigri strains are known to produce mycotoxins. In this study, to confirm the non-production of four major mycotoxins (aflatoxins, ochratoxins, fumonisins, and patulin) by citric acid-producing Aspergillus tubingensis (formerly A. niger) WU-2223L, genome sequence analysis and LC-MS/MS analysis were performed. Although short genetic regions homologous to the biosynthetic gene clusters of ochratoxin A and fumonisin B2 were found in the genome of strain WU-2223L, most of the other parts were missing, indicating that a large portion of the gene clusters were deleted. The genome sequence analysis also revealed that the genomic DNA of the strain WU-2223L possessed no gene homologous to biosynthetic gene clusters for aflatoxins and patulin in addition to ochratoxins and fumonisins. Moreover, the LC-MS/MS analysis on the broth of strain WU-2223L grown in three typical media revealed that none of the four mycotoxins were detected (below the detection limit). Therefore, the non-production of the four major mycotoxins by the strain WU-2223L was confirmed not only based on the genome sequence analysis, but also on the analysis of metabolites of the strain. Our findings indicate that A. tubingensis WU-2223L is a safe and promising strain that can be used for industrial production of valuable metabolites such as citric acid.