Stabilizing effects of bacterial biofilms : EPS penetration and redistribution of bed stability down the sediment profile

This work was supported by the Fundamental Research Funds for the Central Universities of China (Grant Nos. 2017B694X14, 2015B24814, 2016B00714, 2015B15814 and 2015B25614), the National Natural Science Foundation of China (NSFC, Grant Nos. 51579072, 51620105005, 51379003 and 41606104), the Natural Science Foundation of Jiangsu Province (Grant Nos. BK20160862) and the Jiangsu Provincial Policy Guidance Programme (Grant Nos. BY2015002-05). D. M. Paterson received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland funded by the Scottish Funding Council grant reference HR09011) and contributing institutions.Biofilms, consisting of microorganisms and their secreted extracellular polymeric substances (EPS), serve as “ecosystem engineers” stabilizing sedimentary environments. Natural sediment bed provides an excellent substratum for biofilm growth. The porous structure and rich nutrients allow the EPS matrix to spread deeper into the bed. A series of laboratory-controlled experiments were conducted to investigate sediment colonization of Bacillus subtilis and the penetration of EPS into the sediment bed with incubation time. In addition to EPS accumulation on the bed surface, EPS also penetrated downwards. However, EPS distribution developed strong vertical heterogeneity with a much higher content in the surface layer than in the bottom layer. Scanning Electron Microscope (SEM) images of vertical layers also displayed different micro-morphological properties of sediment-EPS matrix. In addition, colloidal and bound EPS exhibited distinctive distribution patterns. After the full incubation, the bio-sedimentary beds were eroded to test the variation of bed stability induced by biological effects. This research provides an important reference for the prediction of sediment transport, and hence deepens the understanding of the biologically mediated sediment system and broadens the scope of the burgeoning research field of “biomorphodynamics”.Publisher PDFPeer reviewe