Microbial Enhancement of the Dissolution Rates of Kaolinite by Interaction of Heterotrophic Bacterium Pseudomonas Fluorescens

Microbes can significantly affect the dissolution rates of silicate minerals on the earth's surface environments. However, there is little information about molecular-level mechanism for enhancement of the dissooution rates by bacterial interaction. To evaluate the effects of bacteria on dissolution rates and to elucidate the molecular-level mechanism, experiments on dissolution of kaolinite in bacterial systems containing Pseudomonas fluorescens were performed in this study. The dissolution experiments were conducted using the batch reactors containing 0.2 g of kaolinite and 100 ml of 10 mM NaCl solution with 10 5 to 10 9 cells/ml of P.fluorescens at 25°C for up to 20 days. The results indicated that the dissolution rates of kaolinite increased by 1.6 to 10.4 times progressively with increasing bacterial concentrations from 10 5 to 10 9 cells/ml, respectively, relative to the bacteria-free control. The concentrations of dissolved Al ions also increased up to approximately log(IAP/K) = 1.7 for saturation indices with respect to gibbsite. The analysis of dissolved organic molecules in the solutions revealed that significant amounts of proteins were released from the bacterial cells along with less or trace amounts of polysaccharides, nucleic acids, and organic acids. Thus, these extracellular organic molecules consisting mainly of proteins are likely to contribute to the enhancement of kaolinite dissolution by electrostatic interaction with the kaolinite surfaces and also by the complxation with the dissolved Al ions.