Abstract

Aspergillus sojae has long been considered a domesticated strain of Aspergillus parasiticus. This study delineated relationships among the two species and an Aspergillus PWE36 isolate. Of 25 examined clustered aflatoxin genes of PWE36, 20 gene sequences were identical to those of A. sojae, but all had variations to those of A. parasiticus. Additionally, PWE36 developmental genes of conidiation and sclerotial formation, overall, shared higher degrees of nucleotide sequence identity with A. sojae genes than with A. parasiticus genes. Examination of defective cyclopiazonic acid gene clusters revealed that the PWE36 deletion pattern was identical only to those of A. sojae. Using A. sojae SMF134 genome sequence as a reference, visualization of locally collinear blocks indicated that PWE36 shared higher genome sequence homologies with A. sojae than with A. parasiticus. Phylogenetic inference based on genome-wide single nucleotide polymorphisms (SNPs) and total SNP counts showed that A. sojae strains formed a monophyletic clade and were clonal. Two (Argentinian and Ugandan) A. parasiticus isolates but not including an Ethiopian isolate formed a monophyletic clade, which showed that A. parasiticus population is genetically diverse and distant to A. sojae. PWE36 and A. sojae shared a most recent common ancestor (MRCA). The estimated divergence time for PWE36 and A. sojae was about 0.4 mya. Unlike Aspergillus oryzae, another koji mold that includes genetically diverse populations, the findings that current A. sojae strains formed a monophyletic group and shared the MRCA with PWE36 allow A. sojae to be continuously treated as a species for food safety reasons.

摘要

酱油曲霉长期以来一直被认为是寄生曲霉的驯化菌株。这项研究描绘了这两个物种和曲霉菌PWE36 分离株之间的关系。在PWE36的25个检测的黄曲霉毒素簇基因中，20个基因序列与酱油曲霉的基因序列相同，但均与寄生曲霉的基因序列有变异。此外，总体而言，PWE36 分生孢子和菌核形成的发育基因与酱油曲霉基因比与寄生曲霉基因具有更高程度的核苷酸序列同一性。对有缺陷的环匹阿尼酸基因簇的检查表明，PWE36 缺失模式仅与A. 大豆。使用酱油曲霉SMF134 基因组序列作为参考，局部共线块的可视化表明，PWE36 与酱油曲霉的基因组序列同源性高于与寄生曲霉的基因组序列同源性。基于全基因组单核苷酸多态性 (SNP) 和总 SNP 计数的系统发育推断表明，酱油曲霉菌株形成单系进化枝并且是克隆的。两个（阿根廷和乌干达）寄生曲霉分离株（不包括埃塞俄比亚分离株）形成了一个单系进化枝，这表明寄生曲霉种群具有遗传多样性，并且与酱油曲霉相距较远。PWE36 和酱油曲霉拥有最近的共同祖先（MRCA）。PWE36 和A. sojae的估计分歧时间约为 0.4 mya。与米曲霉（另一种包含遗传多样性种群的曲霉）不同，目前的酱油曲霉菌株形成了一个单系群，并与 PWE36 共享 MRCA，这一发现使得酱油曲霉能够出于食品安全原因继续被视为一个物种。