Elucidating Adhesion Behaviors and the Interfacial Interaction Mechanism between Plant Probiotics and Modified Bentonite Carriers

Bentonite mineral can be used as the support carrier of microbial inoculant. The promising carrier should have excellent adsorption capacity and affinity for plant probiotics. However, the adhesion mechanisms and interface interaction underlying the bentonite carriers and plant probiotics remain uncertain. In this study, the interface interactions of two kinds of plant growth-promoting bacteria (Rs-2 and SL-44) and five different bentonite carriers were examined. The results indicated that the maximum bacteria adsorption capacity and affinity were obtained by hydrophobic stearic acid-modified bentonite (SA-BENT) owing to its attractive acid–base interaction as calculated by extended-DLVO theory. The stronger acid–base interaction between Rs-2 and the carriers promoted its adhesion, which may be attributed to its more hydrophobic surface structure acting as a broom to remove interfacial water. SL-44 had a stronger adsorption binding energy and smaller adsorption capacity since its EPS components (e.g., low polarity, aromatic lipophilic protein macromolecules) were preferentially absorbed and occupied absorption sites based on the fluorescence excitation–emission matrix (EEM) and normalized volume integral of the fluorescence region.