Hypertonic stress induced changes of Pseudomonas fluorescens adhesion towards soil minerals studied by AFM

Studying bacterial adhesion to mineral surfaces is crucial for understanding soil properties. Recent research suggests that minimal coverage of sand particles with cell fragments significantly reduces soil wettability. Using atomic force microscopy (AFM), we investigated the influence of hypertonic stress on Pseudomonas fluorescens adhesion to four different minerals in water. These findings were compared with theoretical XDLVO predictions. To make adhesion force measurements comparable for irregularly shaped particles, we normalized adhesion forces by the respective cell-mineral contact area. Our study revealed an inverse relationship between wettability and the surface-organic carbon content of the minerals. This relationship was evident in the increased adhesion of cells to minerals with decreasing wettability. This phenomenon was attributed to hydrophobic interactions, which appeared to be predominant in all cell–mineral interaction scenarios alongside with hydrogen bonding. Moreover, while montmorillonite and goethite exhibited stronger adhesion to stressed cells, presumably due to enhanced hydrophobic interactions, kaolinite showed an unexpected trend of weaker adhesion to stressed cells. Surprisingly, the adhesion of quartz remained independent of cell stress level. Discrepancies between measured cell–mineral interactions and those calculated by XDLVO, assuming an idealized sphere-plane geometry, helped us interpret the chemical heterogeneity arising from differently exposed edges and planes of minerals. Our results suggest that bacteria may have a significant impact on soil wettability under changing moisture condition

Copper retention influenced by an invasive and a native plant in riparian soil

Riparian soils are exposed to diverse anthropogenic stressors via aquatic pathways. Our study focuses on the impact of the invasive plant Impatiens glandulifera (Himalayan Balm) on processes that affect the filter and retention function of soils for copper, a regionally applied fungicide.Two soils, overgrown with the invasive I. glandulifera and by the native Urtica dioica were characterized for general soil properties and their copper retention ability assessed by a sequential extraction after seven days flooding with three different copper concentrations.We observed higher values for the absolute copper concentration in all fractions for the soil overgrown with I. glandulifera than for the soil overgrown with U. dioica. However, with respect to the total content, copper was more mobile in soil overgrown with U. dioica despite a higher organic matter content. The lower extraction recovery of the U. dioica soil suggests that more copper was mobilized in colloids which in long-term are easier washed out while I. glandulifera favors immobilization of organically chelated copper enhancing a legacy effect.Our results highlight the plant specific impact possibly induced by root exudates and plant residues affecting soil organic matter quality including the colloidal fraction and thus filter and retention functions of riparian soils