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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Microbial EPS secretion and topography of quasi-naturally grown biofilm originating from a eutrophic lake"

The fine sediments are stabilized by biofilms (“biostabilization”) has various economic and ecological consequences. The highly multifaceted sediment-water system is approximated by several modelling methods considering only characteristic diameters and the density of the sediment grains. The microbial biostabilization significantly impacts fine sediments which complicates simplified modelling solutions for sediment dynamics and management strategies. Thus, these modeling approach is not applicable for sediments with strong biological influence, such as eutrophic reservoir: where biofilms effect are involved on sediment stability. The insights for fresh water such as eutrophic lake are limited, since enormous research are already performed on marine water as it has long been believed that biostabilization which is mainly due to microbially secreted sticky polymers, depends largely on the amount of ions to help binding. Thus, the understanding of growth biofilm and their response with several conditions due to environmental or anthropogenic in fresh water are urged. In the case of the reservoir, especially having several hydrodynamic event like sediment flushing, pump storage reservoir etc, biostabilization becomes more interested to the researcher. Thus Altmühlsee, Bavaria, is considered in this study. In order to understand the formation of biofilm and its stability better, it seems important to have also a closer look at the composition of the EPS. This research demonstrate the importance of biostabilization for fine sediment dynamics and effect of hydrodynamic change on EPS matrix in freshwater biofilms. To investigate natural biofilm growth in freshwater sediments under controlled boundary conditions, experiment is run for growth period (8 weeks) and treatment period (2.5 weeks) in six straight flume experiments with natural fresh water were performed under identical boundary conditions. This unique setup allows comparable biofilm growth under controlled hydrodynamic and environmental conditions, an important requisite for future research on the ecological significance and impact of biostabilization for ecosystem functioning at varying environmental scenarios. Biofilms are cultivated in this sophisticated setup by circulating fresh water, collected from Altmühlsee, over glass beads (d50 = 0.15 mm, ρ = 2.5 t m-3). The impact of hydrodynamics on the EPS of the developed biofilms are analyzed as a proxy of biostabilization. Total EPS is measured responsive with hydrodynamic regime. More precisely, while the proteins are fluctuating, carbohydrates are detected as main keyplayer for significant response of total EPS with hydrodynamic regime. How this response take place depending on quality of EPS and restructuring internal EPS matrix are discussed. This findings emphasize the importance of detailed analyses of the EPS components of the biofilm system.
Keywords: Biofilm; Biostabilization; Extracellular polymeric substances (EPS); Proteins; Carbohydrates; Microbial; Sediment stability; Exopolymers; Bacteria.