Metagenomic analysis of thiocyanate and cyanide biodegrading microbial consortia Metagenome

Gold mining and other industrial activities make extensive use of cyanide (CN-) and produce large volumes of thiocyanate- (SCN-) contaminated wastewater that must be treated before reuse in mining processes. Furthermore, contaminated wastewater stored in tailings dams may pose an environmental threat through the potential for leakage into local groundwater. Microbial communities are often used for biodegradation and environmental remediation, however, little is known about the membership and metabolic potential of SCN-degrading consortia. Application and improvement of the remediation strategy will benefit from an understanding of organisms that can contribute to the breakdown of SCN- into sulfur, carbon and nitrogen compounds. To this end, we performed metagenomic analysis of samples from two laboratory-scale bioreactors used to study SCN- and CN- degradation by established microbial consortia. Community analysis revealed the dominance of Thiobacillus spp. whose genomes harbor a previously unreported operon for SCN- degradation. Metabolic predictions suggest that a large portion of each bioreactor community is autotrophic, relying not on molasses in reactor feed, but using energy gained from oxidation of the sulfur compounds produced during SCN- degradation. Heterotrophs compose a smaller portion of the reactor bacterial community, and predation by phage and eukaryotes is predicted to affect community dynamics. Furthermore, genes for ammonium oxidation and denitrification were detected, possibly allowing removal of nitrogen as required for complete remediation of wastewater. These findings suggest possible optimization strategies for reactor design such as improved aerobic/anaerobic partitioning and elimination of organic carbon from reactor feed.