The engineering potential of natural benthic bacterial assemblages in terms of the erosion resistance of sediments

The secretion of extracellular polymeric substances (EPS) by bacteria has been recognized as important across a wide range of disciplines, but in natural sediments the microalgae have been the most investigated EPS producers and sediment stabilizers. In the present paper, the stabilization potential of a natural benthic bacterial assemblage was tested in cultures growing on non-cohesive glass beads over 5 weeks. The substrate erosion resistance as determined by CSM (Cohesive Strength Meter) and by MFPC (Magnetic Force Particle Capture) was significantly enhanced over time compared to controls. Nutrient enrichment of the bacterial assemblages (bacteria+) resulted in enhanced stabilization (x 3.6) as compared with nutrient-depleted (bacteria) assemblages (x 1.8). This correlated with higher bacterial biomass and EPS concentrations. Substrate stability was thus closely related to bacterial cell numbers (R2 = 0.75 / 0.78) and EPS protein concentrations (R2 = 0.96 / 0.53) (for bacteria / nutrient treatment, respectively), but not to EPS carbohydrates. This study implies more significance for the proteins in substratum cohesion within the EPS complex than previously recognized. The data show the importance of bacterial assemblages for microbial sediment stabilization and secondly, that a change in abiotic conditions can affect their stabilization potential significantly.