Affiliation:
1. Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, Louisiana 70124
2. National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan
Abstract
ABSTRACT
In aflatoxin biosynthesis, the pathway for the conversion of 1-hydroxyversicolorone to versiconal hemiacetal acetate (VHA) to versiconal (VHOH) is part of a metabolic grid. In the grid, the steps from VHA to VHOH and from versiconol acetate (VOAc) to versiconol (VOH) may be catalyzed by the same esterase. Several esterase activities are associated with the conversion of VHA to VHOH, but only one esterase gene (
estA
) is present in the complete aflatoxin gene cluster of
Aspergillus parasiticus
. We deleted the
estA
gene from
A. parasiticus
SRRC 2043, an
O
-methylsterigmatocystin (OMST)-accumulating strain. The
estA-
deleted mutants were pigmented and accumulated mainly VHA and versicolorin A (VA). A small amount of VOAc and other downstream aflatoxin intermediates, including VHOH, versicolorin B, and OMST, also were accumulated. In contrast, a VA-accumulating mutant, NIAH-9, accumulated VA exclusively and neither VHA nor VOAc were produced. Addition of the esterase inhibitor dichlorvos (dimethyl 2,2-dichlorovinylphosphate) to the transformation recipient strain RHN1, an
estA
-deleted mutant, or NIAH-9 resulted in the accumulation of only VHA and VOAc. In in vitro enzyme assays, the levels of the esterase activities catalyzing the conversion of VHA to VHOH in the cell extracts of two
estA
-deleted mutants were decreased to approximately 10% of that seen with RHN1. Similar decreases in the esterase activities catalyzing the conversion of VOAc to VOH were also obtained. Thus, the
estA
-encoded esterase catalyzes the conversion of both VHA to VHOH and VOAc to VOH during aflatoxin biosynthesis.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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