Insight into the adhesion propensities of extracellular polymeric substances (EPS) on the abiotic surface using XDLVO theory

The adhesion of microorganisms is ubiquitous and plays a central role in a wide spectrum of problems, including biomedical study, industrial application and environmental microbiology. To know more about mechanisms underlying microalgal early-stage adhesion, the soluble EPS (sEPS) and the bound EPS (bEPS) of Chlorella vulgaris were extracted and characterized for their adhesion behaviors on the hydrophilic polymethyl methacrylate (PMMA) and the hydrophobic polytetrafluoroethylene (PTFE) surfaces in this work. It was found that the sEPS and the bEPS were dominated by hydrophilic fractions (57.6%) and hydrophobic fractions (49.6%) respectively. As a result, the bEPS always showed a higher adhesion propensity than the sEPS, and its adhesion on PTFE was more significant than that on PMMA. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the adhesion behavior was dominated by the Lewis acid-base interfacial free energy (∆GmwfAB) of algal EPS. The bEPS could promote adhesive propensity of both two materials, whereas the sEPS would repulse the hydrophilic surfaces. Additionally, the dissolved organic carbon (DOC) was shown to be a more suitable index for the description of EPS adhesion. This work presents evidence on the mechanisms of the EPS-mediated adhesion process in algal biofilm formation.