In Situ Stimulation of Thiocyanate Biodegradation through Phosphate Amendment in Gold Mine Tailings Water

Thiocyanate (SCN^–) is a contaminant requiring remediation in gold mine tailings and wastewaters globally. Seepage of SCN^–-contaminated waters into aquifers can occur from unlined or structurally compromised mine tailings storage facilities. A wide variety of microorganisms are known to be capable of biodegrading SCN^–; however, little is known regarding the potential of native microbes for in situ SCN^– biodegradation, a remediation option that is less costly than engineered approaches. Here we experimentally characterize the principal biogeochemical barrier to SCN^– biodegradation for an autotrophic microbial consortium enriched from mine tailings, to arrive at an environmentally realistic assessment of in situ SCN^– biodegradation potential. Upon amendment with phosphate, the consortium completely degraded up to ∼10 mM SCN^– to ammonium and sulfate, with some evidence of nitrification of the ammonium to nitrate. Although similarly enriched in known SCN^–-degrading strains of thiobacilli, this consortium differed in its source (mine tailings) and metabolism (autotrophy) from those of previous studies. Our results provide a proof of concept that phosphate limitation may be the principal barrier to in situ SCN^– biodegradation in mine tailing waters and also yield new insights into the microbial ecology of in situ SCN^– bioremediation involving autotrophic sulfur-oxidizing bacteria.