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Ochratoxin production by Aspergillus ochraceus as affected by methionine and structurally related compounds
Abstract:
When 10(-2) M of L- or D-methionine was added to a synthetic medium containing xylose as the sole carbon source, ochratoxin production by Aspergillus ochraceus was strongly inhibited. At that concentration methionine derivatives, e.g., alpha-methyl-DL-methionine, DL-methionine sulfoxide, and L-methionine sulfone, did not inhibit ochratoxin production, whereas DL-methionine S-methyl sulfonium chloride (MMSC) inhibited ochratoxin production to a large extent. L-Methionine, as well as MMSC, also completely inhibited sclerotia formation, while D-methionine and DL-methionine sulfoxide caused only a partial inhibition. At lower concentrations (10(-3) and 10(-4) M), none of the compounds exhibited inhibitory effects. In cases where strong ochratoxin inhibition was detected, fungal radial growth or mycelial dry weight was inhibited by only 10-25%, while the initial pH of the medium dropped from approximately 6.5 to approximately 4.4-5.0. Adjustment of the initial pH of media supplemented with 10(-2) M L-methionine, D-methionine, or MMSC to a pH of approximately 7.8 did not change the inhibitory effects on ochratoxin production in media containing L-methionine. On the other hand, sclerotia formation was restored in all three treatments.
Insights
Methionine and its derivative DL-methionine S-methyl sulfonium chloride (MMSC) strongly inhibit ochratoxin production in Aspergillus ochraceus. These compounds also affect fungal growth and sclerotia formation, offering potential for mycotoxin control.
Area of Science:
- Mycology
- Food Science
- Biochemistry
Background:
- Ochratoxin A is a potent mycotoxin produced by Aspergillus species.
- Controlling ochratoxin production is crucial for food safety and agricultural economics.
- Methionine metabolism may influence secondary metabolite production in fungi.
Purpose of the Study:
- To investigate the effect of L-methionine, D-methionine, and their derivatives on ochratoxin production by Aspergillus ochraceus.
- To assess the impact of these compounds on fungal growth, sclerotia formation, and pH.
- To determine the specificity of methionine's inhibitory action.
Main Methods:
- Aspergillus ochraceus cultures were grown in synthetic media with xylose as the carbon source.
- Various concentrations of L-methionine, D-methionine, and methionine derivatives were added.
- Ochratoxin production, fungal radial growth, mycelial dry weight, sclerotia formation, and pH were measured.
Main Results:
- 10(-2) M L-methionine, D-methionine, and DL-methionine S-methyl sulfonium chloride (MMSC) strongly inhibited ochratoxin production.
- Methionine derivatives like alpha-methyl-DL-methionine and DL-methionine sulfoxide showed no significant inhibition.
- L-Methionine and MMSC completely inhibited sclerotia formation; D-methionine and DL-methionine sulfoxide partially inhibited it.
- Fungal growth inhibition was minimal (10-25%) despite significant ochratoxin reduction.
- Adjusting the initial pH did not alter the inhibitory effects of L-methionine on ochratoxin production but restored sclerotia formation.
Conclusions:
- Methionine and MMSC are effective inhibitors of ochratoxin biosynthesis in Aspergillus ochraceus.
- The inhibitory effect is specific to certain methionine forms and concentrations.
- These findings suggest potential strategies for managing ochratoxin contamination in food and agriculture.