Thiocyanate biodegradation: harnessing microbial metabolism for mine remediation

Thiocyanate (SCN–) forms in the reaction between cyanide (CN–) and reduced sulfur species, e.g. in gold ore processing and coal-coking wastewater streams, where it is present at millimolar (mM) concentrations. Thiocyanate is also present naturally at nM to µM concentrations in uncontaminated aquatic environments. Although less toxic than its precursor CN–, SCN– can harm plants and animals at higher concentrations, and thus needs to be removed from wastewater streams prior to disposal or reuse. Fortunately, SCN– can be biodegraded by microorganisms as a supply of reduced sulfur and nitrogen for energy sources, in addition to nutrients for growth. Research into how we can best harness the ability of microbes to degrade SCN– may offer newer, more cost-effective and environmentally sustainable treatment solutions. By studying biodegradation pathways of SCN– in laboratory and field treatment bioreactor systems, we can also gain fundamental insights into connections across the natural biogeochemical cycles of carbon, sulfur and nitrogen.