Bacteria play an important role in bio-desilication of high silica bauxites. However, low bio-desilication efficiency and unknown mechanisms limit the use of bacteria in bio-desilication of bauxite. In this study, two highly effective Si-solubilizing bacteria (Arthrobacter pascens H19 and Burkholderia anthina G21) were obtained and characterized for their impact on Si and Al release from a high-silica (18.1%) bauxite and the mechanisms involved. Dissolved Si and Al concentrations in the culture medium were 3.3-13.9 mM and 0.04-0.41 mM, and total Si and Al released from the bauxite were 2.76-11.64 mg and 0.03-0.39 mg, respectively, in the presence of these strains. Strain G21 released more Si from the bauxite than strain H19 at the end of the experiment. These strains produced malic (791-1700 mu M), citric (94-447 mu M), and succinic (228-494 mu M) acids, and expolyssaccharides (EPS) (39-420 mg L-1) during the bio-desilication processes. Furthermore, strain G21 produced more organic acids (19-65%) than strain H19, while strain H19 produced more EPS (1.7-4.9-fold) than strain G21. The metabolites (fermentation broth, organic acids, and EPS) of these strains also significantly increased dissolved Si concentration compared to the control. Notably, the ratios of Al2O3 to SiO2 in the bauxite treated with strains H19 and G21 were 9.14 and 9.64, respectively, which met the requirement in the Bayer process for alumina production. The results showed distinct and high bio-desilication effectiveness of these strains and suggested that the highly effective Si-solubilizing bacterial strains increased bio-desilication efficiency through the production of organic acids and EPS.