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The regulation of citrinin biosynthesis in Penicillium
Project
Project code: MRI-OG-08-54401RegCitPen
Contract period: 01.06.2015
- 31.03.2018
Purpose of research: Basic research
The formation of citrinin in foods can be due to three important Penicillium species: P. verrucosum, P. expansum and P. citrinum. All species have different capacities to produce citrinin. First results also show drastic differences in the regulation of citrinin biosynthesis in the three species. While the biosynthesis of citrinin is strongly regulated in P. verrucosum and P. expansum, e. g. its production is strongly dependent on the environmental conditions, this seems not to be the case with P. citrinum, which rather produces citrinin constitutively.
Penicillium expansum is the most important post-harvest fungal pathogen, leading to green rot of apples, which may lead to high economic losses. Besides this problem, P. expansum is able to produce two important mycotoxins, in particular patulin and citrinin. Patulin can usually be found in quite high amounts in the apple matrix. This is not the case for citrinin, which often cannot be detected in rotten apples or only at much lower amounts. According to literature data patulin is a pathogenicity factor, supporting the colonization of apples by the fungus. About the role of citrinin nothing was known when the project started. Within the project the biological role of the biosynthesis of citrinin by P. expansum could be almost unraveled. The production of citrinin supports the colonization of apples by P. expansum, too. Citrinin however, is apparently not absolutely necessary for colonization, but supports the process under certain conditions. It could be shown that citrinin is produced on apples only very lately during the growth phase of P. expansum. While patulin can already be detected after 4 days, citrinin can only be found after 10 to 12 days, despite the fact that both toxin biosynthetic gene clusters are active from the beginning of the observation period. This indicates, that citrinin may also be produced early, but may bind to the apple matrix or maybe derivatized. A detailed analysis about the fate of citrinin in apples revealed that these two processes are responsible for this effect. Experiments have shown, that citrinin can bind tightly to pectin. After this binding, citrinin is no longer extractable and amenable for analytical detection. Furthermore it could be shown, that citrinin is degraded by the ROS (reactive oxygen species), which are produced by the plant themselves as protectant against fungal attack. Citrinin is degraded to three; as yet unknown metabolites by these plant ROS. Because of these two mechanisms only after prolonged incubation citrinin can be detected analytically in the apples. This is related to the formation of aerial mycelium and spores. That means that only the citrinin, produced in the aerial mycelium seems to be detectable by analytical methods. Citrinin produced in the substrate mycelium, e. g. in the apple is bound to pectin or derivatized. With the aid of the gene knockout technology P. expansum strains were generated, which were no longer able to produce citrinin. During infection experiments it could be shown, that these strains could produce small rotting areas, but were, in contrast to the wild type, not able to completely rot the apple. The addition of external citrinin restored this capacity to that of the wild type. These results show that the environment in the natural habitat can even support citrinin biosynthesis. Publications: Geisen, R., Schmidt-Heydt, M., Stoll, D., Touhami, N., 2018. Aspects of the occurrence, genetics and regulation of biosynthesis of the three Food relevant Penicillium mycotoxins: Ochratoxin A, Citrinin and Patulin. In: The Mycota XV: Physiology and Genetics, 2nd Edition, Eds. T. Anke and A. Schlüßler, Springer, Cham, 413–433. Touhami, N., Soukup, S.T., Schmidt-Heydt, M., Kulling, S.E., Geisen, R., 2018. Citrinin as an accessory establishment factor of Penicillium expansum for the colonization of apples. Int. J. Food Microbiol. 266, 224–233. Geisen, R., Schmidt-Heydt, M., Touhami, N., Himmelsbach, A., 2018. New aspects of ochratoxin and citrinin biosynthesis in Penicillium. Curr. Opin. Food Sci. eingereicht. Geisen, R., Touhami, N., Schmidt-Heydt, M., 2017. Mycotoxins as adaptation factors to food related environments. Curr. Opin. Food Sci. 17, 1–8. Congress contributions Touhami, N., Stoll, D., Schmidt-Heydt, M., Geisen, R., 2016. De-regulating citrinin biosynthesis of Penicillium expansum by heterologous expression of the ctnR gene of Penicillium citrinum. International Committee of Food Mycology Meeting, Freising, 12–15. Juni 2016. Stoll, D., Touhami, N., Geisen, R., Schmidt-Heydt, M., 2016. WGS Sequencing of the citrinin producer Penicillium citrinum and subsequent characterization of the citrinin gene cluster. 38th Mycotoxin Workshop, Berlin. Geisen, R., Schmidt-Heydt, M., Touhami, N., 2017. Understanding in situ regulation of mycotoxin biosynthesis to improve food safety. Deutsch-chinesicher Workshop Food Security and Food Safety. Guangzhou/Shanghai, 10–13. April.
Section overview
Subjects
- Food microbiology
- Toxicology
Framework programme
Funding programme
Excutive institution
MRI - Department of Safety and Quality of Fruit and Vegetables (MRI-OG)
