Aflatoxin biosynthesis gene clusters and flanking regions.
1U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, 1100 Robert E. Lee Boulevard, PO Box 19687, New Orleans, LA 70179, USA. ehrlich@srrc.ars.usda.gov
Journal of Applied Microbiology
|August 20, 2005
Summary
The complete aflatoxin (AF) biosynthetic gene cluster sequences of major AF-producing Aspergillus species are highly conserved, suggesting AFs have adaptive value. This study provides the first complete sequence comparison, aiding understanding of AF biosynthesis regulation.
Area of Science:
- Mycology and Molecular Biology
- Genomics and Bioinformatics
- Biochemistry and Natural Product Synthesis
Background:
- Aflatoxins (AFs) are toxic secondary metabolites produced by Aspergillus species.
- Understanding the genetic basis of AF biosynthesis is crucial for controlling contamination and its impact.
- Comparative genomics of AF biosynthetic gene clusters can reveal evolutionary insights and regulatory mechanisms.
Purpose of the Study:
- To compare the complete nucleotide sequences of the biosynthetic gene clusters responsible for aflatoxin production in key Aspergillus species.
- To establish phylogenetic relationships and assess the evolutionary conservation of these gene clusters.
- To identify conserved and variable regions within the AF gene cluster and infer functional and regulatory implications.
Main Methods:
- Sequencing of fosmid clones selected by homology to Aspergillus parasiticus AF gene cluster.
- Sequence alignment and comparative analysis of gene order and content across different Aspergillus species.
- Phylogenetic analysis using the maximum likelihood method (PAUP) to determine evolutionary relationships.
Main Results:
- Gene order is conserved across the AF gene clusters of Aspergillus nomius, A. parasiticus, A. flavus, and an unnamed Aspergillus sp.
- The A. flavus-type AF gene cluster has been maintained for at least 25 million years, indicating strong selective constraints.
- The ver-1 gene shows distinct evolutionary pressures compared to other pathway genes, and a four-gene sugar utilization cluster is conserved, suggesting functional linkage.
Conclusions:
- The high conservation of AF biosynthesis gene cluster components suggests a significant adaptive advantage for AF production in specific ecological niches.
- This comprehensive comparison of complete AF gene cluster sequences is the first of its kind, offering a foundation for understanding AF biosynthesis regulation.
- The findings will aid in developing strategies to control AF production in both experimental and natural settings.
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