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.