Mechanical and chemical studies on EPS from Sulfobacillus thermosulfidooxidans: from planktonic to biofilm cells

Abstract

Bacteria attach to minerals and form biofilms, which can initiate and enhance bioleaching. Extracellular polymeric substances (EPS) play a crucial role during the whole process. Little is known how the cell surface/EPS mechanically and chemically respond to transformation from planktonic to biofilm cells. In this study the attachment and biofilm formation by Sulfobacillus thermosulfidooxidans were followed during pyrite leaching. Adhesiveness and stiffness of the cell/biofilm and the pyrite surface were checked by atomic force microscopy (AFM) in force mapping mode under real living conditions. The EPS components were analysed by colorimetry, fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. The results indicate that slimy and soft EPS heterogeneously accumulated in the biofilms and on the surface of pyrite to induce bacterial adhesion and form robust biofilms. After attaching to the pyrite surface, the cells started to change the components of their EPS. Huge amounts of humic substances were detected in the biofilm EPS.