Comparative genome analysis of Aspergillus flavus clinically isolated in Japan
Takahito Toyotome1,2,3,4, Saho Hamada1, Satoe Yamaguchi3
1Department of Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
Abstract:
Aspergillus flavus is an important zoonotic pathogen and a well-known aflatoxin producer. Aspergillus flavus strains that are prevalent in Japanese environments are reported to be non-aflatoxigenic, although their aflatoxin productivity, especially among clinical isolates, has not been thoroughly investigated to date. In this study, we sequenced the genomes of ten strains of A. flavus isolated in Japan and compared their sequences with each other as well as with those of Aspergillus oryzae RIB40 and A. flavus NRRL3357. The phylogenetic analysis based on identified SNPs indicated that five strains were closer to A. oryzae RIB40 than to A. flavus NRRL3357. In contrast, of those isolates that were closer to A. flavus NRRL3357 than to A. oryzae RIB40, three were found to possess either the entire or partial aflatoxin biosynthesis gene cluster of NRRL3357-type. Furthermore, two of the three actually produced either aflatoxin B1 or an intermediate of the reaction leading to aflatoxin formation. Three of the ten strains we isolated were identified to possess part of the aflatoxin gene cluster, while five others retained the A. oryzae RIB40-type cluster. The genome data thus obtained may be further explored and utilized for comparative analysis of aflatoxin production in environmental and clinical isolates of A. flavus.
Insights
Japanese Aspergillus flavus strains were analyzed for aflatoxin production. Some clinical isolates possess the aflatoxin gene cluster and produce aflatoxins, challenging previous assumptions about environmental strains.
Area of Science:
- Mycology
- Genomics
- Food Safety
Background:
- Aspergillus flavus is a significant zoonotic pathogen and a known producer of aflatoxins.
- Japanese environmental strains of A. flavus are often considered non-aflatoxigenic, but their aflatoxin productivity, especially in clinical settings, requires further investigation.
Purpose of the Study:
- To investigate the aflatoxin productivity of Japanese Aspergillus flavus isolates.
- To compare the genomes of Japanese A. flavus strains with known aflatoxigenic and non-aflatoxigenic strains.
Main Methods:
- Whole-genome sequencing of ten Japanese A. flavus strains.
- Phylogenetic analysis using single nucleotide polymorphisms (SNPs).
- Comparison with Aspergillus oryzae RIB40 and A. flavus NRRL3357 genomes.
Main Results:
- Phylogenetic analysis revealed five strains were more closely related to A. oryzae RIB40.
- Three strains closer to A. flavus NRRL3357 harbored the aflatoxin biosynthesis gene cluster.
- Two of these three strains produced aflatoxin B1 or its intermediates.
Conclusions:
- Some Japanese Aspergillus flavus clinical isolates possess the genetic capacity for aflatoxin production.
- This finding necessitates a re-evaluation of aflatoxin risk associated with environmental A. flavus strains in Japan.
- Genome data provides a basis for further comparative studies on aflatoxin production.
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