Effect of Kluyveromyces thermotolerans on polyketide synthase gene expression and ochratoxin accumulation by Penicillium and Aspergillus

Abstract

In a previous study, it was demonstrated that Kluyveromyces thermotolerans strains can reduce both growth and ochratoxin A (OTA) accumulation by Aspergillus section Nigri strains. There is no information about the mechanisms related to this reduction. A viable hypothesis can be that the presence of biocontrol agents can affect OTA biosynthesis by influencing the transcriptional activity of the polyketide synthase (pks) gene, one of the key enzymes in the OTA biosynthetic pathway. The aims of this work were to determine the effect of two selected strains of K. thermotolerans as potential biocontrol agents and to evaluate if their presence can affect the otapks gene expression of ochratoxigenic Aspergillus and Penicillium species. Growth, OTA and ochratoxin B (OTB) biosynthesis by the fungal strains at the phenotypic and molecular levels were monitored. The results obtained showed that both K. thermotolerans strains evaluated had a strong influence on growth, OTA and OTB biosynthesis, and expression of the mycotoxin biosynthesis genes. However, no direct correlation between the influence of the biocontrol yeasts on pks gene expression, OTA and OTB production could be found. These results could indicate an inhibitory mechanism by the yeasts, which apparently involve a post-transcriptional mechanism. The data obtained could imply that the production of mycotoxins can be regarded as a kind of adaptation mechanism to environmental stress conditions by these mycotoxigenic species.