Affiliation:
1. Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, Louisiana
2. Division of Plant Pathology and Microbiology, Department of Plant Sciences, University of Arizona, Tucson, Arizona
Abstract
ABSTRACT
Aspergillus flavus
isolates produce only aflatoxins B1 and B2, while
Aspergillus parasiticus
and
Aspergillus nomius
produce aflatoxins B1, B2, G1, and G2. Sequence comparison of the aflatoxin biosynthesis pathway gene cluster upstream from the polyketide synthase gene,
pksA
, revealed that
A. flavus
isolates are missing portions of genes (
cypA
and
norB
) predicted to encode, respectively, a cytochrome P450 monooxygenase and an aryl alcohol dehydrogenase. Insertional disruption of
cypA
in
A. parasiticus
yielded transformants that lack the ability to produce G aflatoxins but not B aflatoxins. The enzyme encoded by
cypA
has highest amino acid identity to
Gibberella zeae
Tri4 (38%), a P450 monooxygenase previously shown to be involved in trichodiene epoxidation. The substrate for CypA may be an intermediate formed by oxidative cleavage of the A ring of
O
-methylsterigmatocystin by OrdA, the P450 monooxygenase required for formation of aflatoxins B1 and B2.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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