PDF《northern Germany)》

AQUATIC MICROBIAL ECOLOGY Aquat Microb Ecol Vol.

51: 97C103,

2008 doi: 10.3354/ame01188 Published April

24 INTRODUCTION Extracellular peroxidases are enzymes that are mainly produced by micro-organisms such as basid- iomycetous white-rot fungi and related litter- decomposing fungi, and also by Actinobacteria and plants (Tuomela et al. 2000). The best studied extra- cellular enzymes of white-rot fungi are lignin peroxi- dases, manganese peroxidases and laccases. In addi- tion to these enzymes other extracellular peroxidases are known that are comparable to horseradish peroxi- dase in structure and reactivity (Petersen et al. 1993). In the presence of hydrogen peroxide, these proteins act on aromatic compounds such as humic substances, resulting in the formation of unstable radicals. These radicals participate in chemical reactions leading to bond cleavage and thus degradation of aromatic com- pounds. Most known extracellular peroxidase-produc- ing organisms have been isolated from terrestrial habi- tats (Tuomela et al. 2000, Hatakka 2001);

few studies focus on extracellular peroxidase-producing organ- isms in the aquatic environment (De Haan 1976, Sins- abaugh et al. 1992). In the abovementioned investiga- tions peroxidases were detected as contributors to ? Inter-Research

2008 ・ www.int-res.com *Email: ubuck@mpi-bremen.de Extracellular peroxidase activity in an experimentally divided lake (Gro?e Fuchskuhle, northern Germany) Ulrike Buck1, 3,*, Hans-Dietrich Babenzien1 , Elke Zwirnmann2

1 Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Department of Limnology of Stratified Lakes, Alte Fischerhuette 2,

16775 Stechlin, Germany

2 Central Chemical Laboratory, Mueggelseedamm 310,

12587 Berlin, Germany

3 Present address: Max Planck Institute of Marine Microbiology, Department of Molecular Ecology, Celsiusstr. 1,

28359 Bremen, Germany ABSTRACT: Extracellular peroxidases act on aromatic compounds such as humic substances result- ing in the formation of unstable radicals. Most organisms that are known to produce extracellular peroxidases are terrestrial, e.g. the wood-rotting fungus Phanerochaete chrysosporium and the Actinobacterium Streptomyces viridosporus. Only few studies focus on the action of these enzymes in the aquatic environment. In this study, the activities of extracellular peroxidases in

2 distinct com- partments of the experimentally divided Lake Gro?e Fuchskuhle, Germany (an acidic humic rich compartment and an almost neutral eutrophic compartment) and in the catchment area were inves- tigated. Additionally, the effects of pH on extracellular peroxidase activity and of the size fractions of water samples associated with extracellular peroxidase activity were determined. Enzyme activity and the characterisation of the enzymes were assayed by oxididation of 2,2'

-azino-di-(3-ethyl- benzthiazoline-6-sulphonic acid) (ABTS). In the humic rich compartment, extracellular peroxidase activity was (except for

1 month) significantly higher than in the eutrophic compartment, with high- est activities during fall and winter. In contrast, no peroxidase activity was detected in the catchment area. The pH optimum of extracellular peroxidases was pH 3, and highest activity was detected in the

10 kDaC0.2 ?m molecular weight class. Thus we documented the occurrence of extracelluar peroxi- dases in Lake Gro?e Fuchskuhle and suggest that these enzymes are involved in the degradation of aromatic compounds such as humic substances. KEY WORDS: Extracellular peroxidase ・ Exoenzymes ・ ABTS ・ Humic substances ・ Catchment area Resale or republication not permitted without written consent of the publisher Aquat Microb Ecol 51: 97C103,