Microorganisms and functional genes in an aerobic-anoxic integrated gold mine wastewater treatment system

Biological treatment of cyanide-contaminated wastewater is mediated by microbial consortia in which different organisms perform distinct, functionally specialized roles. This study investigated microbial communities involved in gold mine wastewater treatment with integrated aerobic-anoxic reactors seeded with consortia from an alkaline soda lake, Lake Chitu. Whole-genome sequencing of isolates (WGS) and metagenomic sequencing of the bioreactor were performed to characterize the consortia, resulting in the identification of 23 non-redundant genomes, comprising 14 whole-genome sequencing isolates and 19 metagenome-assembled genomes (MAGs). Most isolated genomes were similar to the recovered metagenomes of MAGs. Except for Alkalibacterium, all isolates possessed one or more genes potentially involved in cyanide or cyanate transformation, along with at least one type of terminal oxygenase; however, the gene encoding cynD, which is required for the direct hydrolysis of free cyanide (CN⁻), was not detected. Three representative Halomonas isolates harboured the nitrate reductase narGHI, nitrite reductase nirS, nitric oxide reductase norB/norC, and nitrous-oxide reductase nosZ genes for full denitrification. All of the isolates possessed several gene clusters associated with different heavy metal resistances. This study suggests that the microbial inoculum sourced from Lake Chitu harbors diverse microorganisms possessing genes potentially involved in cyanide-related metabolic pathways. The findings of this study add to our understanding of the alkaliphilic microbial population that degrades cyanide and cyanide intermediates and provide insight into how these organisms break down cyanide and resist cyanide and heavy metal inhibitory effects.