Extracellular peroxidase activity in an experimentally divided lake (Grosse Fuchskuhle, northern Germany)

Extracellular peroxidases act on aromatic compounds such as humic substances resulting 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 compartments of the experimentally divided Lake Grosse Fuchskuhle, Germany (an acidic humic rich compartment and an almost neutral eutrophic compartment) and in the catchment area were investigated. 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 highest 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 kDa-0.2 mu m molecular weight class. Thus we documented the occurrence of extracelluar peroxidases in Lake GroBe Fuchskuhle and suggest that these enzymes are involved in the degradation of aromatic compounds such as humic substances.