An investigation of bacterial interaction forces and bacterial adhesion to porous media.

摘要

Bacterial adhesion in porous media was studied through a progression of experiments, from a macroscopic investigation of bacterial transport to a microscopic investigation of bacterial interaction forces. In the macroscopic portion of this work, our goal was to identify conditions under which the transport of bacteria in porous media was the greatest. The effects of flow velocity, cell concentration, cell motility, solution ionic strength, and some chemicals on bacterial transport were examined. Atomic force microscopy (AFM) was used to image bacterial cells that had been exposed to adhesion-modifying chemicals, to determine the feasibility of using these treatments. Tapping-mode images in air of Pseudomonas stutzeri KC and Burkholderia cepacia G4 revealed that the surfactant Tween 20 and low ionic strength water did not damage cellular morphology, while disodium tetraborate and sodium pyrophosphate caused substantial damage to the cells, and therefore should not be used in bacterial transport studies.; Although enhancements in bacterial transport could be made through modification of macroscopic parameters, the conclusions made from these experiments were not sufficient to allow us to formulate a mechanism describing bacterial attachment to soil. A microscopic approach was taken to directly measure the bacterial interaction forces that control the adhesion process. AFM was used to measure the interaction forces between individual, negatively-charged bacteria and silicon nitride to determine the effects of pH, ionic strength, and the presence of bacterial surface polymers on interaction forces. Bacterial surface polymers dominated interactions between bacteria and AFM silicon nitride tips. The measured forces were represented well by an electrosteric repulsion model accounting for repulsion between the tip and bacterial polymers, but were much larger in magnitude and extended over longer distances (100's of nanometers) than predicted by DLVO theory. Partially removing polysaccharides from the bacterial surfaces resulted in lower repulsive forces that decayed much more rapidly. The magnitude of the measured forces in these experiments and the equilibrium lengths predicted by the electrosteric model are comparable to other force measurements and size estimates on polymers and polysaccharides. The results of the AFM force measurements were discussed in terms of their implications regarding bacterial transport in porous media.