Intraspecific variability of HOG1 phosphorylation in Penicillium verrucosum reflects different adaptation levels to salt rich habitats

Mycotoxin biosynthesis in Penicillium verrucosum is modulated by different molecular regulation mechanisms. One important mechanism is the HOG1 (high osmolarity glycerol) MAP kinase signaling pathway. In a comparative analysis three different P. verrucosum strains were selected from six strains with different ability to produce the mycotoxins ochratoxin and citrinin. The fungal strains were grown on laboratory medium supplemented with different concentrations of NaCl. It could be shown that there exists an interrelationship between the growth rate, the level of HOG phosphorylation and the mycotoxin biosynthesis under the respective growth condition. The weak to non ochratoxin producing P. verrucosum strain, BFE875, showed only a poor growth rate but the strongest HOG1 phosphorylation; the strong ochratoxin and citrinin producing strain BFE575 showed a reasonable HOG1 phosphorylation with an average growth rate; and the strong ochratoxin and weak citrinin producing strain BFE495 showed only a poor phosphorylation but the highest growth rate in 7days of incubation at 25°C. The magnitude of phosphorylation of the HOG1 protein seems to be inversely correlated with the degree of adaption of the fungus to hyperosmotic growth conditions.