A UNIVERSAL METHOD FOR ISOLATING MINERAL-SPECIFIC BACTERIA FOR SULFIDE MINERALS

A method was developed to obtain cultures of bacteria specific to selected sulfide minerals, as part of a study on the use of bacteria as floatation reagents. Two bacterial cultures (grown on pyrite and chalcopyrite concentrates) were placed in shake flasks containing slurries of either pure pyrite or pure chalcopyrite. These cultures were transferred sequentially from one slurry to the next to select mineral-specific bacteria. Pyrite-specific bacteria were selected as bacteria that adhered to pyrite, but not chalcopyrite. Chalcopyrite-specific bacteria were selected by retention in chalcopyrite slurries, but not pyrite. Three round of selection produced cultures that are mineral-specific. Epifluorescence microscopy confirmed the specificity of these cultures to their respective minerals. The isolates thus obtained were chemotactic, swimming up concentration gradients towards iron or copper. A key advance in this study was the use of solutions containing sulfide to detach and recover bacteria attached to sulfide minerals. Water, mineral salts and tripolyphosphate/Tween (a non-ionic detergent) cannot detach these strongly-adhering bacteria. This suggests that sulfides on the mineral surfaces play a role in bacterial attachment.

The study found that cultures of mineral-specific bacteria can enhance the floatation separation of purified pyrite and chalcopyrite in a mixture, but not their separation from concentrate or ores.

In principle, this method can be universally applied to obtain bacteria that adhere to one, but not other selected mineral sulfides.