Different transport behaviors of Bacillus subtilis cells and spores in saturated porous media: Implications for contamination risks associated with bacterial sporulation in aquifer.

In this study, we compared the transport characteristics of Bacillus subtilis cells and their spores in saturated porous media. Both the bacteria cells and spores were readily transported under lower ionic strengths (IS) (1mM), featuring high mass recovery rates (>75%). The bacteria cells recovery rate declined to 58.05% when the IS increased to 100mM; but the spores recovery rate remained at 74.54%. Spores appear to be more mobile than bacterial cells over wide range of IS. Surface properties and breakthrough curves analysis of the two bio-particles (cells and spores) indicated that attachment, straining and blocking mechanisms contribute differently to deposition processes. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further indicated that the particles attachment may primarily occurred at the secondary energy minimum. More important, XDLVO calculations showed that the dominant forces changed with IS, altering the efficiency of particles attachment. The electric double layer repulsion mainly controlled particle deposition at 1mM. In contrast, the van der Waals attraction and Lewis acid-base interactions dominated particle deposition at 100mM. This study showed that spores are more mobile than bacteria cells in subsurface environment. Given that spores form under harsh environmental conditions, we must consider spore formation and transport when groundwater microbial contamination occurs.