"Microbial engineers control sediment dynamics in aquatic habitats (Abstract)"Background. Sediments and their microbial communities (biofilms) feature to a great extend the essential functionality of marine and freshwater habitats and provide important “ecosystem services” such as nutrient (re)-cycling or self-purification. This study addresses the ecosystem function “biostabilisation” where the microorganisms modify the response of the aquatic sediments to erosive forces (flow velocity, turbulence) by the secretion of extracellular polymeric substances (EPS).
Methods. The colonization of natural assemblages of estuarine bacteria and diatoms, as well as freshwater biofilms, was studied over several weeks using non-cohesive glass beads (< 63µm) as an artificial substratum. The adhesion capacity and the substratum stability of the growing biofilms has been determined by Magnetic Particle Induction (MagPI) and Cohesive Strength Meter (CSM), respectively. In parallel, bacterial cell numbers, microalgal biomass, the composition of the bacterial and microalgal assemblages as well as EPS quantity and quality (carbohydrates, proteins) have been monitored.
Results. Microbial colonization resulted in significant enhancement of adhesion and stability of the substratum as compared to the controls (up to a factor of 12) irrespective of the environment (freshwater, marine). The stabilization potential of the bacteria exceeded that of the axenic diatom assemblages; however, the overall stabilization was highest in mixed assemblages. The assemblage composition, their physiology and the secretion of EPS quantity and quality were important for sediment stabilization, but strongly influenced by changing abiotic conditions.