title: Oxidative stress induces the biosynthesis of citrinin by Penicillium verrucosum at the expense of ochratoxin.
abstract: Penicillium verrucosum is a fungus that can produce ochratoxin A and citrinin, two structurally related nephrotoxic mycotoxins. P. verrucosum usually occurs on wheat but can occasionally also be found in NaCl rich habitats such as salted cheeses or olives, indicating that this fungus can adapt to different environments. The ratio of ochratoxin A to citrinin produced by P. verrucosum is shifted to one of either mycotoxin at the expense of the other dependent on the environmental conditions. High NaCl concentrations shift secondary metabolite biosynthesis towards ochratoxin A production. P. verrucosum copes with NaCl stress by increased ochratoxin A biosynthesis, ensuring chloride homeostasis. Ochratoxin A carries chlorine in its molecule and can excrete chlorine from the cell. It was further shown that the regulation of ochratoxin A by high NaCl conditions is mediated by the HOG MAP kinase signal transduction pathway. Here it is shown that high oxidative stress conditions, evoked for example by increasing concentrations of Cu(2+) cations in the growth medium, shift secondary metabolite biosynthesis of P. verrucosum from ochratoxin A to citrinin. The production of citrinin normalizes the oxidative status of the fungal cell under oxidative stress conditions leading to an adaptation to these environmental conditions and protects against increased oxidative stress caused by increased Cu(2+) concentrations. Moreover citrinin also protects against light of short wavelength, which may also increase the oxidative status of the environment. The biosynthesis of citrinin is apparently regulated by a cAMP/PKA signaling pathway, because increasing amounts of external cAMP reduce citrinin biosynthesis in a concentration dependent manner. These conditions lead to the cross-regulation of the ochratoxin A/citrinin secondary metabolite pair and support the adaptation of P. verrucosum to different environments.
authors.affiliation: Max Rubner-Institut; Department of Safety and Quality of Fruit and Vegetables; Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Schmidt-Heydt
authors.affiliation: Max Rubner-Institut; Department of Safety and Quality of Fruit and Vegetables; Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany.
authors.forename: Dominic
authors.initials: D
authors.lastname: Stoll
authors.affiliation: Max Rubner-Institut; Department of Safety and Quality of Fruit and Vegetables; Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schütz
authors.affiliation: Max Rubner-Institut; Department of Safety and Quality of Fruit and Vegetables; Haid-und-Neu-Str. 9, 76131 Karlsruhe, Germany. Electronic address: rolf.geisen@t-online.de.
authors.forename: Rolf
authors.initials: R
authors.lastname: Geisen
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D002953:Citrinin / Q000096:biosynthesis*; D017753:Ecosystem; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D009793:Ochratoxins / Q000378:metabolism*; D018384:Oxidative Stress; D010407:Penicillium / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D009793:Ochratoxins; C025589:ochratoxin A; D002953:Citrinin; D012965:Sodium Chloride
keywords: Adaptation; Citrinin; Ochratoxin; Oxidative stress; Penicillium verrucosum; cAMP