Soil Culturable Bacteria Increase the Water-Soluble Fluoride Content in the Soil

To evaluate the effects of soil bacteria on the contents of water-soluble fluoride in the soil in high fluoride area, a total of 225 isolates were firstly obtained from the soil collected from Xianghuangqi County in Inner Mongolia, an typical high fluoride area in China. These isolates were grouped into 10 operational taxonomic units according to their 16SrRNA gene sequences using 97% sequence identity threshold. An isolate was randomly selected from each group as the representative strain to study their mineral weathering potentials, calcium precipitating potentials, and their effect on the content of water-soluble fluoride in the soil. Most of the representative strains showed the silicate mineral weathering capacities and all showed the calcium precipitating capacities. The results of the soil column experiment showed the concentration of water-soluble fluoride in majority of the bacteria-inoculated soils (8 out of 10) increased compared to abiotic control after two weeks' incubation. The increases in the fluoride content were closely correlated with a reduction of water-soluble calcium contents and/or an increase of pH, suggesting that calcium precipitation by these bacteria could be an important factor to elevate the content of water-soluble fluoride content in soil. This work would deepen our understanding of the microbial contribution to the formation of high fluoride groundwater.