| Cyanide and its derivatives are the main agents used to extract gold from gold ores.The gold dressing slag left over after gold extraction is typically placed in a tailings pond.Due to extreme weather and geological disasters,the tailings pond can become deformed,the anti-seepage structure can be damaged,and ground precipitation can penetrate into the tailings pond,resulting in surface water or groundwater pollution.Cyanide and heavy metals are often the main pollutants found in tailings pond leachate.Currently,research on cyanide-degrading bacteria mainly focuses on the domestication of activated sludge and the degradation of coking wastewater or simulated wastewater with high concentrations of organic matter and potassium cyanide.However,there are few studies on the isolation and cultivation of in situ microorganisms from gold cyanide tailings reservoirs and the degradation of cyanide-containing wastewater with low organic matter and heavy metal in gold cyanide tailings leaching solutions.In this paper,the tailings pond area of a gold mine in Gansu was selected as the research object,and soil samples,leachate,and leachate sediment samples were collected.The heavy metal pollution and soil quality in the tailings area were investigated by measuring the heavy metals and physical and chemical indexes of the samples,and 16 S amplicon sequencing was performed on the samples to analyze the microbial community in the tailings pond area.Cyanide-degrading functional bacteria were cultured and screened from the leachate sediment,and their genome sequencing and bioinformatics analysis were performed.The results showed that:(1)According to the Nemero single-factor index evaluation of heavy metal pollution in tailings pond soil,mercury pollution is the most severe,accounting for 100%of the samples.Arsenic and cadmium pollution levels are relatively high,with 21.43%and 47.62% of samples being heavily polluted,and 16.67% and 42.86% being moderately polluted,respectively.Mild pollution was observed in 52.38% and 9.52%of the samples for nickel and zinc,while 57.14% and 52.38% of the samples showed mild pollution overall.In this area,mercury pollution is significant,followed by relatively serious arsenic and cadmium pollution.Nickel and zinc pollution are present to a certain extent,while copper and lead pollution are negligible.Additionally,the concentration of heavy metals varies with soil depth and the order of tailings ponds.Due to the excessively high single-factor pollution index of mercury,the Nemerow composite index evaluation result indicates that all 43 samples are heavily polluted,suggesting an unfavorable heavy metal pollution situation in the tailings pond.Moreover,cyanide from the tailings pond soil migrates to the tailings pond leachate,leading to an excessive total cyanide concentration in the leachate.The overall soil in the tailings pond and surrounding environment was found to be alkaline or weakly alkaline.Additionally,the comprehensive fertility of the tailings pond soil was found to be poor and inferior to the surrounding environmental background.Moreover,the comprehensive longitudinal fertility of the tailings pond soil was found to be the highest in the shallow soil,followed by the middle soil,and lowest in the deep soil.(2)Through the analysis of bacterial diversity in soil,leachate,and leachate sediment samples from a tailings pond,it can be observed that microbial diversity in soil samples is significantly higher compared to that in leachate and leachate sediment.Furthermore,heavy metal pollution has been found to reduce microbial diversity.The dominant bacterial groups in the tailings pond soil were Bacteroidota,Acidobacteriota,and Bacteroidota.At the genus level,the dominant bacteria were Pseudomonas,Achromobacter,and Rlastonia,respectively.The results of gate horizontal clustering are as follows: FCPU426 exhibited a relatively high relative abundance in sample 3-3,Fusobacteriota and Firmiculosis in sample 9-3,Deferribacterota and GAL15 in sample10-2,and Thermoplasmatota in sample 12-1.Additionally,there was a relatively high relative abundance of Spirochaetota in samples 12-3 and Campilobacterota in leachate bottom mud.At the genus level,the results showed the presence of Nitrosomonas,CandidatusTenderia,Candidatus-Nitrotoga,Thiobacillus,Hydrogenophaga,and Pseudophaga in the leachate sludge.The relative abundance of env.OPS-17 was higher,while the relative abundance of Pseudomonas and Bacteroides was higher in the leachate.(3)The number of colonies in the leachate sludge from the tailings reservoir is43,600 CFU/g,indicating a significant presence of microorganisms.Among the 12 strains of indigenous microorganisms isolated from the bottom mud of the percolate,three showed promising degradation capabilities towards cyanide.The phylogenetic tree analysis of these three strains revealed that CDB3 exhibited the highest similarity to Corynebacterium Marine,while CDB5 and CDB7 shared the highest similarity to Exiguobacterium.Through genome sequencing and bioinformatics analysis,we discovered that these strains possess various metabolic pathways and decomposition enzymes,enabling them to degrade cyanide and tolerate heavy metal stress.These findings provide fundamental data and theoretical support for further research on the degradation mechanism and potential application of these strains under conditions of heavy metal stress. |
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