Fluorite Dissolution by a Phosphate-Solubilizing Bacterium Isolated from Groundwater of Xianghuangqi County, Inner Mongolia, China

Abstract

Xianghuangqi County of Inner Mongolia is a typical high-fluoride area in China. Present work discussed a possible role of phosphate-solubilizing bacteria (PSBs) in the formation of high-fluoride groundwater in this area. An indigenous PSB was isolated from the local groundwater. Analysis of 16S rDNA sequence indicates that the bacterium belongs to the Pseudomonas genus. This bacterium caused acidification of the culture media under phosphate-limited conditions. HPLC analysis detected several metabolites that are likely to acidify the cultural media. Fluorite dissolution experiment with this bacterium in minimum medium containing 2 mg/L, 20 mg/L, and 200 mg/L glucose showed that the initial concentration of glucose has a large effect on pH of the culture medium and the fluorite dissolution rate. The pH of bacterial cell-free medium remained constant throughout the experiment. Introduction of the PSB caused an initial decrease in pH, followed by an increase. The measured pH minima were 4.8, 5.8, and 6.0 for culture media amended with 200 mg/L, 20 mg/L, and 2 mg/L glucose, respectively. A slow increase of the fluoride concentration in bacterial cell-free medium was observed, and inoculation of the PSB increased the rate of fluoride release causing the concentration of fluoride in bacterial-inoculated medium to markedly exceed that found in control medium. The highest fluorite dissolution rate was observed in culture medium amended with 200 mg/L glucose, while the rates observed in culture medium amended with 20 mg/L and 2 mg/L glucose were comparable. Given the ubiquity of PSBs in natural environment, these findings show PSBs could be important contributors to fluoride mobilization in high fluoride area.