Location: Food and Feed Safety Research
Title: Cloning and Characterization of the Aspergillus ochraceoroseus Aflatoxin Biosynthetic Gene Cluster Authors
Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2007
Publication Date: N/A
Technical Abstract: Production of the carcinogenic mycotoxin aflatoxin B1 has been reported from members of Aspergillus section Flavi, Aspergillus section Nidulantes, and a newly proposed section, Aspergillus section Ochraceorosei that consists of Aspergillus ochraceoroseus and the closely related A. rambellii. A. ochraceoroseus (Ao) has been shown to accumulate both aflatoxin (AF) and the aflatoxin precursor sterigmatocystin (ST). Past studies using Southern hybridization of Ao genomic DNA with A. nidulans ST gene probes demonstrated the presence of ST gene homologs in Ao. Knowing that the A. nidulans ST gene cluster is organized quite differently from that of the A. flavus AF gene cluster, we set out to determine the genetic organization of the Ao AF biosynthetic cluster. Sequencing of a number of overlapping Ao genomic DNA lambda clones that hybridized with A. nidulans ST genes allowed the Ao AF gene cluster to be cloned and characterized. Sequence analysis of the Ao AF gene cluster showed that it contained genes that were homologous to those of the A. nidulans ST gene cluster and that, for the most part, the genes were organized in the same manner with respect to gene order and direction of transcription when compared to that of the ST gene cluster. In general, all of the Ao AF cluster genes demonstrated fairly high nucleotide and amino acid identity to their A. nidulans ST cluster gene homologs. No genes sharing similarity to the A. flavus aflQ (ordA) and aflP (omtA) genes that are required for conversion of ST to AF in A. flavus were found within the sequenced regions of the Ao AF gene cluster. Attempts to identify these two gene homologs by either PCR amplification or Northern hybridization (using A. parasiticus aflQ and aflP gene probes) were not successful. Data presented will compare and contrast characteristics of the Ao gene cluster to that of the A. nidulans ST cluster and it will also provide additional insights into the evolution of the AF gene cluster among the known AF-producing Aspergilli.