Identification of O-methylsterigmatocystin as an aflatoxin B1 and G1 precursor in Aspergillus parasiticus
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Abstract:
An isolate of Aspergillus parasiticus CP461 (SRRC 2043) produced no detectable aflatoxins, but accumulated O-methylsterigmatocystin (OMST). When sterigmatocystin (ST) was fed to this isolate in a low-sugar medium, there was an increase in the accumulation of OMST, without aflatoxin synthesis. When radiolabeled [14C]OMST was fed to resting mycelia of a non-aflatoxin-, non-ST-, and non-OMST-producing mutant of A. parasiticus AVN-1 (SRRC 163), 14C-labeled aflatoxins B1 and G1 were produced; 10 nmol of OMST produced 7.8 nmol of B1 and 1.0 nmol of G1, while 10 nmol of ST produced 6.4 nmol of B1 and 0.6 nmol of G1. A time course study of aflatoxin synthesis in ST feeding experiments with AVN-1 revealed that OMST is synthesized by the mold during the onset of aflatoxin synthesis. The total amount of aflatoxins recovered from OMST feeding experiments was higher than from experiments in which ST was fed to the resting mycelia. These results suggest that OMST is a true metabolite in the aflatoxin biosynthetic pathway between sterigmatocystin and aflatoxins B1 and G1 and is not a shunt metabolite, as thought previously.
Insights
O-methylsterigmatocystin (OMST) is a key intermediate in aflatoxin biosynthesis. Studies show OMST is converted to aflatoxins B1 and G1, confirming its role in the pathway.
Area of Science:
- Mycology
- Biochemistry
- Molecular Biology
Background:
- Aspergillus parasiticus produces aflatoxins, potent mycotoxins harmful to health.
- The biosynthetic pathway of aflatoxins is complex and not fully elucidated.
- Sterigmatocystin (ST) and O-methylsterigmatocystin (OMST) are known precursors.
Purpose of the Study:
- To investigate the role of OMST in the aflatoxin biosynthetic pathway.
- To determine if OMST is a direct precursor or a shunt metabolite in aflatoxin production.
- To clarify the metabolic relationship between ST, OMST, and aflatoxins B1 and G1.
Main Methods:
- Culturing Aspergillus parasiticus strains, including a non-aflatoxin-producing mutant (AVN-1).
- Feeding experiments using sterigmatocystin (ST) and radiolabeled O-methylsterigmatocystin ([14C]OMST).
- Analysis of aflatoxin and intermediate metabolite production using chromatography and radiolabeling.
Main Results:
- Aspergillus parasiticus CP461 accumulated OMST but not aflatoxins.
- Feeding [14C]OMST to AVN-1 resulted in the production of aflatoxins B1 and G1.
- OMST feeding yielded higher amounts of aflatoxins B1 and G1 compared to ST feeding.
- Time-course studies indicated OMST synthesis precedes aflatoxin production.
Conclusions:
- O-methylsterigmatocystin (OMST) is a direct and essential intermediate in the aflatoxin biosynthetic pathway.
- OMST is converted to aflatoxins B1 and G1, positioning it between sterigmatocystin (ST) and aflatoxins.
- These findings establish OMST as a true metabolite, not a shunt product, in aflatoxin formation.