Abstract
Ochratoxin A (OTA), a potentially carcinogenic mycotoxin which contaminates grains, is produced by several Aspergillus species. A comparative sequence analysis of the OTA-producing Aspergillus ochraceus fc-1 strain and other Aspergillus species was performed. Two new OTA-related polyketide synthase (PKS) (AoOTApks) genes were identified. The predicted amino acid sequence of AoOTApks-1 displayed high similarity to previously identified PKSs from OTA-producing A. carbonarius ITEM 5010 (67%; [PI] No. 173482) and A. niger CBS 513.88 (62%; XP_001397313). However, the predicted amino acid sequence of AoOTApks-2 displayed lower homology with A. niger CBS 513.88 (38%) and A. carbonarius ITEM 5010 (28%). A phylogenetic analysis of the β-ketosynthase and acyl-transferase domains of the AoOTApks proteins indicated that they shared a common origin with other OTA-producing species, such as A. carbonarius, A. niger, and A. westerdijkiae. A real-time reverse-transcription PCR analysis showed that the expression of AoOTApks-1 and -2 was positively correlated with the OTA concentration. The pks gene deleted mutants ∆AoOTApks-1 and ∆AoOTApks-2 produced nil and lesser OTA than the wild-type strain, respectively. Our study suggests that AoOTApks-1 could be involved in OTA biosynthesis, while AoOTApks-2 might be indirectly involved in OTA production.
Highlights
Ochratoxin A (OTA) is one of the most important mycotoxins produced by several species of Aspergillus and Penicillium that naturally occur in a variety of food commodities prior to harvest or, more commonly, during storage
The key pks genes associated with OTA biosynthesis in A. ochraceus, designated AoOTApks, were predicted by a comparative genomic analysis based on the genome-wide sequencing of A. ochraceus fc-1
Two pks genes, designated AoOTApks-1 and AoOTApks-2, which are probably involved in OTA biosynthesis, were identified
Summary
Ochratoxin A (OTA) is one of the most important mycotoxins produced by several species of Aspergillus and Penicillium that naturally occur in a variety of food commodities prior to harvest or, more commonly, during storage. According to the OTA structure and its proposed biosynthetic pathway, OTA synthesis requires several proteins, including a polyketide synthase (PKS). The key portion of these biosynthetic reactions is a repetitive decarboxylative condensation similar to the chain elongation step in fatty acid biosynthesis [12]. Based on their protein architectures, PKSs are classified into three basic types. In this study, based on the sequenced genome of A. ochraceus, two pks genes, designated AoOTApks-1 and AoOTApks-2, were predicted to be involved in OTA biosynthesis. Understanding the mechanistic differences between the two pks genes can help us to explore the OTA biosynthetic pathway and develop novel gene diagnostic strategies, based on pks genes, to prevent OTA contamination
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