<i>In Situ</i> Stimulation of Thiocyanate Biodegradation through Phosphate Amendment in Gold Mine Tailings Water

Thiocyanate (SCN<sup>–</sup>) is a contaminant requiring remediation in gold mine tailings and wastewaters globally. Seepage of SCN<sup>–</sup>-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<sup>–</sup>; however, little is known regarding the potential of native microbes for <i>in situ</i> SCN<sup>–</sup> biodegradation, a remediation option that is less costly than engineered approaches. Here we experimentally characterize the principal biogeochemical barrier to SCN<sup>–</sup> biodegradation for an autotrophic microbial consortium enriched from mine tailings, to arrive at an environmentally realistic assessment of <i>in situ</i> SCN<sup>–</sup> biodegradation potential. Upon amendment with phosphate, the consortium completely degraded up to ∼10 mM SCN<sup>–</sup> to ammonium and sulfate, with some evidence of nitrification of the ammonium to nitrate. Although similarly enriched in known SCN<sup>–</sup>-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 <i>in situ</i> SCN<sup>–</sup> biodegradation in mine tailing waters and also yield new insights into the microbial ecology of <i>in situ</i> SCN<sup>–</sup> bioremediation involving autotrophic sulfur-oxidizing bacteria.