Comparative genome analysis of Aspergillus flavus clinically isolated in Japan.

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.