Location: Food and Feed Safety ResearchTitle: Are current Aspergillus sojae strains originated from native aflatoxigenic Aspergillus species population also present in California?
|Chang, Perng Kuang|
|SHENG T. HUA, SUI - Retired ARS Employee|
Submitted to: Mycobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2023
Publication Date: 6/8/2023
Citation: Chang, P.-K., Sheng T. Hua, S. 2023. Are current Aspergillus sojae strains originated from native aflatoxigenic Aspergillus species population also present in California? Mycobiology. https://doi.org/10.1080/12298093.2023.2217495.
Interpretive Summary: The koji mold Aspergillus sojae has long been considered a domesticated strain of aflatoxigenic Aspergillus parasiticus. This study, using a comparative genomics approach, delineated genome similarity and dissimilarity between the two species. It gives insight into the evolutionary origin of A. sojae. An aflatoxigenic isolate, PWE36, has been accessioned to NCBI as A. parasiticus, but has greater phylogenetic distance from A. parasiticus than A. sojae, with whom it shares the most recent common ancestor. Unlike Aspergillus oryzae, another koji mold that includes genetically diverse populations, A. sojae forms a monophyletic group. These findings allow A. sojae, used for food safety reasons, to be treated as an unambiguous species.
Technical Abstract: Genome-wide single nucleotide polymorphisms (SNPs) of three A. sojae and four A. parasiticus isolates including a presumptive A. parasiticus isolate, PWE36, were obtained. SNP counts and concatenated total SNP sequences were used to infer their phylogenetic relationships. The counts consistent with the SNP sequences showed that current A. sojae isolates were clonal strains and formed a monophyletic clade. Two out of the four A. parasiticus isolates, not including PWE36, formed another monophyletic clade, which suggests that A. parasiticus population is genetically diverse. Sequence homology analysis indicated by collinear blocks showed that genome sequences of the A. sojae isolates were highly homologous. Compared to that of A. sojae SMF134, degrees of homology for the A. parasiticus isolates (not including PWE36) were much lower; various sequence translocations also were present. The PWE36 genome sequence was more homologous to those of the A. sojae isolates than to the A. parasiticus isolates. Additionally, deletions in the cyclopiazonic acid gene clusters as well as molecular defects in both the polyketide synthase gene, (pksA/aflC), and the aflatoxin pathway regulatory gene, aflR, indicated that PWE36 and the A. sojae isolates shared a most recent common ancestor and were distant to the A. parasiticus isolates.