Differences in the Regulation of Ochratoxin A by the HOG Pathway in Penicillium and Aspergillus in Response to High Osmolar Environments

Penicillium verrucosum, P. nordicum and Aspergillus carbonarius are three important ochratoxin A producing species. P. verrucosum is in addition able to produce citrinin. It has been shown earlier that P. nordicum is adapted to NaCl rich environments like salt rich dry cured foods or even salines. In this organism, the biosynthesis of ochratoxin A plays an adaptive role in this habitat. P. verrucosum generally can be found on cereals, but occasionally also on salt rich dry cured foods. In contrast A. carbonarius usually cannot be found in NaCl rich environments, but it occurs in another environment with high concentration of solutes, e.g., in sugar rich substrates like grapes and grape juices. Usually osmotic challenging conditions activate the HOG MAP kinase signal cascade, which in turn activates various osmo-regulated genes. In the current analysis, it could be demonstrated that in case of P. nordicum and P. verrucosum the NaCl induced production of ochratoxin A is correlated to the phosphorylation status of the HOG MAP kinase. Just the opposite was true for A. carbonarius. In this case, also higher amounts of NaCl in the medium lead to an increased phosphorylation status of HOG, but no increase in ochratoxin biosynthesis was observed. In contrast to the Penicillia, higher NaCl concentrations lead to a rapid cessation of growth by A. carbonarius. High glucose concentrations have much less impact on growth and the phosphorylation of HOG.