Adhesion of Pseudomonas putida onto kaolinite at different growth phases

Bacterial adhesion to minerals in soils and sediments is of fundamental importance in mineral weathering and formation, soil aggregate stability, organic matter degradation and the fate of pollutants. Bacterial surface properties are considered to govern adhesion, and these properties likely change as a function of bacterial growth phase. However, the effect of growth stage on bacterial adhesion to clay minerals remains unclear. This work examined the influence of growth phase on the adhesion of Pseudomonas putida to kaolinite-coated coverslips. Fluorescence microscopy, together with a bacterial viability stain, was used to directly quantify surface cell density and viability of adhered P. putida. In situ attenuated total reflectance Fourier transform infrared spectroscopy was applied to yield molecular information about the characteristics of the bacteria, and the adsorption and desorption kinetics. Stationary-phase cells exhibited a higher adsorption density on kaolinite surfaces than mid-exponential-phase cells under static deposition conditions. Compared with the mid-exponential-phase cells, the stationary-phase cells displayed higher saturation coverage, and we fitted the results using a pseudo-first-order kinetics equation. The greater extent of adhesion of the stationary-phase cells was probably due to their smaller cell size and less negative surface charges compared with the cells from other growth stages, which resulted in deeper secondary energy minima and lower energy barriers for adhesion. The results from this study suggest that growth phase may strongly influence cell mobility and biofilm formation in aqueous geochemical environments.