Thiocyanate (SCN–) contamination threatens aquatic ecosystems and pollutes vital freshwater supplies. SCN–-degrading microbial consortia are commercially adapted for remediation, but the impact of organic amendments on selection within SCN–-degrading microbial communities has not been investigated. Here, we tested whether specific strains capable of degrading SCN– could be reproducibly selected for based on SCN– loading and the presence or absence of added organic carbon. Complex microbial communities derived from those used to treat SCN–-contaminated water were exposed to systematically increased input SCN concentrations in molasses-amended and -unamended reactors and in reactors switched to unamended conditions after establishing the active SCN–-degrading consortium. Five experiments were conducted over 790 days, and genome-resolved metagenomics was used to resolve community composition at the strain level. A single Thiobacillus strain proliferated in all reactors at high loadings. Despite the presence of many Rhizobiales strains, a single Afipia variant dominated the molasses-free reactor at moderately high loadings. This strain is predicted to break down SCN– using a novel thiocyanate desulfurase, oxidize resulting reduced sulfur, degrade product cyanate to ammonia and CO2 via cyanate hydratase, and fix CO2 via the Calvin–Benson–Bassham cycle. Removal of molasses from input feed solutions reproducibly led to dominance of this strain. Although sustained by autotrophy, reactors without molasses did not stably degrade SCN– at high loading rates, perhaps due to loss of biofilm-associated niche diversity. Overall, convergence in environmental conditions led to convergence in the strain composition, although reactor history also impacted the trajectory of community compositional change.
Thiocyanate (SCN -) contamination threatens aquatic ecosystems and pollutes vital fresh water supplies. SCNdegrading microbial consortia are commercially deployed for remediation, but the impact of organic amendments on selection within SCNdegrading microbial communities has not been investigated. Here, we tested whether specific strains capable of degrading SCNcould be reproducibly selected for based on SCNloading and the presence or absence of added organic carbon. Complex microbial communities derived from those used to treat SCNcontaminated water were exposed to systematically increased input SCN concentrations in molasses-amended and -unamended reactors and in reactors switched to unamended conditions after establishing the active SCNdegrading consortium. Five experiments were conducted over 790 days and genomeresolved metagenomics was used to resolve community composition at the strain level. A single Thiobacillus strain proliferated in all reactors at high loadings. Despite the presence of many Rhizobiales strains, a single Afipia variant dominated the molasses-free reactor at moderately high loadings. This strain is predicted to breakdown SCNusing a novel thiocyanate dehydrogenase, oxidize resulting reduced sulfur, degrade product cyanate (OCN − ) to ammonia and CO2 via cyanase, and fix CO2 via the Calvin-Benson-Bassham cycle. Removal of molasses from input feed solutions reproducibly led to dominance of this strain. Neither this Afipia strain nor the thiobacilli have the capacity to produce cobalamin, a function detected in low abundance community members. Although sustained by autotrophy, reactors without molasses did not stably degrade SCNat high loading rates, perhaps due to loss of biofilm-associated niche diversity. Overall, convergence in environmental conditions led to convergence in the strain composition, although reactor history also impacted the trajectory of community compositional change.
During the processing of refractory gold ores, cyanide (CN-) and residual sulphur species react to form an effluent stream containing thiocyanate (SCN-) and residual CN-. The release of SCN- and CN- containing effluent water to the environment is prohibited, necessitating effective treatment prior to discharge and/or reuse of contaminated plant water. Biologically mediated effluent remediation processes have been developed for commercial use, to remediate SCN- containing effluents, with the aim of enabling recycling of process water and improving the quality of effluent water prior to disposal. Bioremediation processes to treat these effluents rely on a complex consortium of microorganisms to metabolise the SCN- resulting in the production of ammonium that is in turn removed by conversion to nitrite and subsequent denitrification. Increasingly, genomic methods are being used to investigate processes in wastewater treatment to identify key microbial species and, thereby, inform the rationale design and operation of these bioremediation systems. The microbial ecology of laboratory-based SCN- degrading bioprocesses have been investigated, using genome resolved metagenomics, to provide detailed information on the community composition and metabolic profile of abundant microbial community members. Our on-going research is focused on developing a greater understanding of the heterotrophic and autotrophic populations of microorganisms within the SCN- degrading community as well as the role of the component members in SCN- destruction. We are interested in the formation of microbial biofilm and the spatial distribution of key microorganisms within the resulting biofilm communities. This information is being used to inform further rational development of SCN- degradation processes for treatment of contaminated wastewater effluents.
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