UV induzierte toxische Effekte von gelösten Huminstoffen auf Süßwasserorganismen
Zusammenfassung der Projektergebnisse
For decades, phototoxic potential of irradiated humic substances (HS) and their beneficial UV-light protection for freshwater organisms resulted in conflicting discussions. Therefore, we wanted to gain further insights into underlying mechanisms of phototoxicity, and specific environmental conditions resulting in adverse effects of irradiated HS. Two aspects formed the focus of this study: (a) the quantitative evaluation of transient and stable reactive oxygen species (ROS) and radicals generated via UV irradiation of humic matter and (b) experiments studying effects of oxygen radicals on aquatic organisms of different trophic levels. In order to take the enormous variety in chemical quality of HS into account, we tested a wide range of HS types. We selected for the photoactive material and aimed to establishing potential structure-activity relationships. All experiments with organisms as well as quantification of ROS were performed under similar conditions to allow for comparability. A combination of exposure and irradiation tests with dapnids (D. magna and D. pulex), different strains of cyanobacteria species (Mircocystis aeruginosa, Aphanizomenon flosaquae), 3 green algae (Desmodesmus subspicatus, Scenedesmus obliquus, Chlorella spec) and natural bacteria as well as isolates yielded information on oxygen radical sensitive organisms of the three trophic levels. 1) Due to different strategies to combat photo-induced oxidative stress, sensitivities to phototoxicity of the tested organisms varied depending on their ecological behavior (i.e. escaping strategies) and their physiological and biochemical activities. Further, differences in sensitivity of green algae belonging to different genera (Dictyosphaerium, Mucidosphaerium and Mychonastes) are obvious (Leunert et al. in preparation) indicating variable adaptation to photo-generated oxygen radicals. 2) Phototoxicity of HS is not restricted to UVC-irradiation but also occurs under solar irradiation (UVB, UVA, VIS), whereby different irradiation led to differences in formation rates of short- and long-lived oxygen radicals. Here, we present the first timeresolved measurements of phosphorescence in humic waters. Both lab and field experiments revealed that short- (e.g. singlet oxygen) and long-lived (e.g. hydrogen peroxide) oxygen radicals lead to pronounced differences in bacterial community composition in humic matter rich Lake Grosse Fuchskuhle. 3) The phototoxicity of HS can be related to their potential to generate ROS by solar irradiation. For Daphnia magna no phototoxicity could be observed in irradiated and pre-irradiated humic water at environmental relevant radical and light doses. However, phototoxicity was increased for D. magna juveniles (cultured with a diet of yeast) and D. pulex when incubated in the lowest molecular weight fraction of the fractionated humic water. This low molecular weight fraction was most reactive in formation of ROS, i.e. of H2O2 and 1O2. However, ROS concentrations generated by UV from HS are not sufficiently high enough to harm daphnids grown under natural conditions, but highlight the importance of HS for photoprotection of the animals. 4) Our experiments with cyanobacteria clearly demonstrated that not spectral range of irradiation, but number and type of ROS (formed upon irradiation) are important. For cyanobacteria a strong correlation of adverse effects and UV-light induced H2O2-formation occurred. Singlet oxygen, however, seems not to affect cyanobacteria. The use of the delayed fluorescence (DF) decay kinetics has been proven as a suitable tool for dose-response experiments with cyanobacteria as well with green algae. The use of this method has the potential to rapidly test for photo-induced and other environmental stress, which is often increased due to anthropogenic pollution or water withdrawal. Our study points to the importance of photo-induced oxygen radical stress and its consequences for biodiversity and function of aquatic organisms. New physiological mechanisms and enzymes in response to oxygen radical stress could be of potential interest for biotechnological applications.
Projektbezogene Publikationen (Auswahl)
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Arsenic Redox Changes by Microbially and Chemically Formed Semiquinone Radicals and Hydroquinones in a Humic Substance Model Quinone. Environmental Science & Technology, Vol. 43. 2009, Issue 10, pp. 3639–3645.
Jiang, J; Bauer, I; Paul, A, and Kappler, A.
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Bacteria disperse hitch hiking on zooplankton. Proc. Nat. Acad. Sci. (PNAS), vol. 107. 2010, no. 26, pp. 11959-11964.
Grossart, H.-P., Dziallas, C., Leunert, F., Tang, K.
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Ecological consequences of bacterioplankton lifestyles: Changes in
concepts are needed. (invited minireview for Environ. Microbiol.),
Environmental Microbiology Reports, Vol. 2. 2010, Issue 6, pp. 706–714.
Grossart, H.-P.
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Enrichment and cultivation of pelagic bacteria from a humic lake using phenol and humic matter additions. FEMS Microbiology Ecology, Vol. 72. 2010, Issue 1, pp. 58–73.
Hutalle-Schmelzer, K., Zwirnmann, E., Krüger, A., Grossart, H.-P.
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Extracellular electron transfer through microbial reduction of solid-phase humic substances. Nature Geoscience, Vol. 3. 2010, Issue 6, pp. 417- 421.
Kappler A., Bauer I., Jiang J., Paul, A. Stoesser R., Roden E
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Linkage between crustacean zooplankton and aquatic bacteria.
Aquatic Microbiol Ecology, Vol. 61. 2010, pp. 261-277, AME Special 4.
Tang, K., Turk,V., Grossart, H.-P.
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Singlet oxygen, a neglected but important environmental factor: Short-term and long-term effects on bacterioplankton composition in a
humic lake. Environmental Microbiology, Vol. 12. 2010, Issue 12, pp. 3124–3136.
Glaeser, S., Grossart, H.-P., Glaeser, J.
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www.aquaticmicrobial.net.
Communicative & Integrative Biology, Vol. 3. 2010, Issue 6, pp. 491-494, Mini-Reviews.
Grossart, H.-P., Tang, K.
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Rhodoferax-related pufM gene cluster dominates the aerobic anoxygenic phototrophic communities in German freshwater lakes.
Environmental Microbiology, Vol. 13. 2011, Issue 11, pp. 2865–2875.
Salka, I., Cuperová, Z., Mašín, M., Koblížek, M., Grossart, H.-P.
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UV irradiation of natural organic matter (NOM): impact on organic carbon and bacteria. Aquatic Sciences, Vol. 74. 2012, Issue 3, pp. 443-454.
Paul, A., Dziallas, C, Zwirnmann, E., Gjessing, E.T., Grossart, H.P.
