Biodegradation of cyanide using a Bacillus subtilis strain isolated from artisanal gold mining tailings

Abstract

Artisanal and small-scale mining are informal activities used as a source of family income in many countries, mostly in developing regions. They also represent rudimentary practices that generate environmental and health impacts. In these activities, gold is the main mineral extracted commonly using cyanide leaching as the main technique in their production process, despite its environmental impacts. Biodegradation is an alternative technology that has shown advantages over other techniques; however, most microorganisms studied in cyanide biodegradation processes do not tolerate alkaline environments. Thus, the present study assessed the cyanide biodegradation potential under alkaline conditions of a native strain isolated from an artisanal gold mine. The methodology used consisted in the following steps: isolation of bacteria, identification of the isolated strain, adaptation to alkaline environments, and cyanide degradation tests. The strain was identified using the mass spectrometry technique (MALDI-TOF) and it was subsequently compared with the 16S rDNA sequencing technique. Degradation assays were performed with adapted bacteria in an agitated flask containing a synthetic solution with 500 mg.L⁻¹ of free-cyanide (CN⁻) and initial cell concentration of 2.5 × 10¹¹ CFU.mL⁻¹. Incubation was performed in orbital agitation at 27 °C and 190 rpm for 120 h. In conclusion, the identification techniques elucidated that the isolated strain probably belongs to the Bacillus subtilis species. Finally, cyanide degradation assays showed that the B. subtilis strain adapted to alkaline environments was able to degrade 100% of the free-cyanide in the solution in three days.