Genome-resolved metagenomics of an autotrophic thiocyanate-remediating microbial bioreactor consortium

Abstract Industrial thiocyanate (SCN - ) waste streams from gold mining and coal coking have polluted environments worldwide. Modern SCN - bioremediation involves use of complex engineered heterotrophic microbiomes. No study has tested the ability of a simple environmental autotrophic microbiome to biodegrade SCN - . Here we present results from a bioreactor experiment inoculated with SCN - -loaded mine tailings, incubated autotrophically, and subjected to a range of environmentally relevant conditions. Genome-resolved metagenomics revealed that SCN - hydrolase-encoding, sulphur-oxidizing autotrophic bacteria mediated SCN - degradation. These microbes supported metabolically-dependent non-SCN - -degrading sulphur-oxidizing autotrophs and non-sulphur oxidising heterotrophs, and “niche” microbiomes developed spatially (planktonic versus sessile) and temporally (across changing environmental parameters). Bioreactor microbiome structures changed significantly with increasing temperature, shifting from Thiobacilli to novel SCN - hydrolase-encoding gammaproteobacteria. Transformation of carbonyl sulphide (COS), a key intermediate in global biogeochemical sulphur cycling, was mediated by plasmid-hosted CS 2 and COS hydrolase genes associated with Thiobacillus , revealing a potential for horizontal transfer of this function. Our work shows that simple native autotrophic microbiomes from mine tailings can be employed for SCN - bioremediation, thus improving the recycling of ore processing waters and reducing the hydrological footprint of mining.