Evaluation of Different Amino Acids on Growth and Cyanide Production by Bacillus megaterium for Gold Recovery

Abstract

Bio-cyanidation, as a sustainable and effective method to extract gold from primary and secondary resources, has attracted attention because of its environmental friendliness and economic benefits. The effect of amino acids on bio-cyanide production using Bacillus megaterium (B. megaterium) is a less explored area in this field and is the main interest of this study. Here, the effect of glycine, threonine, and glutamine over a concentration range of 0 to 10 g/L was investigated. The results showed at equal concentration of amino acids (5 g/L), glycine yields (maximum ca. 110 mg/L) a higher concentration of biogenic cyanide (bio-CN), while glutamine and threonine produce less (maximum ca. 74 mg/L and ca. 64 mg/L, respectively). For the first time, optimization of mixing the three amino acids was investigated and revealed more significant roles for glycine and glutamine in stimulation of bio-CN by B. megaterium. The interactions involved in the biosynthesis of bio-CN were explained with a reference to metabolic pathways and the cycle of the bacteria. In mixed amino acids, the optimum medium for bio-CN production was identified to be 2.84 g/L glycine, 3.0 g/L glutamine in the absence of threonine, which could produce a high concentration of ca. 86 mg/L bio-CN, resulting in gold leaching efficiency comparable to chemical cyanide.