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Institut für Wasser- und Umweltsystemmodellierung - IWS



"The effect of light intensity and shear stress on microbial biostabilization and the community composition of natural biofilms"

Biofilms constitute a central issue in microbial ecology due to their high ecological and economic relevance but the impact of abiotic conditions and microbial key players on the development and functionality of a natural biofilm is still hardly understood. This study investigated the effects of light intensity (LI) and bed shear stress (BSS) and the role of dominant microbes during the formation of natural biofilms and particularly the process microbial biostabilization. A comprehensive analysis of microbial biomass, produced extracellular polymeric substances (EPS), as well as the identification of dominant bacterial and algal species was correlated to the assessment of the biofilm adhesiveness/ stability. LI and BSS impacted the biofilms in very different ways: biofilm adhesiveness significantly increased with LI and decreased with BSS. Moreover, microbial biomass and the functional organization of the bacterial community increased with LI while the dynamics in the bacterial community increased with BSS. Most stable biofilms were dominated by sessile diatoms like Achnanthidium minutissimum or Fragilaria pararumpens, and bacteria with either filamentous morphology like Pseudoanabaena biceps or a potential high capacity for EPS production like Rubrivivax gelatinosus. In contrast, microbes with high motility like Nitzschia fonticola or Pseudomonas fluorescens and Caulobacter vibrioides dominated the least adhesive biofilms. Their movement and potential antibiotics production could have had a disruptive impact on the biofilm matrix which decreased its stability. This is the first study to unveil the link between abiotic conditions and resulting shifts in microbial key players to impact the ecosystem service microbial biostabilization.