| Non-ferrous metal(loid)tailings of Guangxi Zhuang autonomous region(China)are typical toxic sources of contamination that can have negative impacts on local human health and regional ecosystems.However,how to cost-effectively carry out the In Situ microbial-treatment of tailings is still a global challenge.The objectives of present study were to investigate the spatial and temporal distribution of bacterial communities at four active and nine abandoned metal(loid)tailings,as well seven abandoned tailings sites(aged 3 and 31 years old)undergoing natural attenuation.We also conducted an in-situ biotreatment of tailings using a combined microbial consortium of sulfate reducing bacteria.Here we show that the tailings sites were nutrient poor or even oligotrophic.Average metal contents of the tailing samples exceeded environmental quality standards for soils.As well,the organic contaminants were mainly containing persistent organic pollutants,such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls.Arenimonas,specific in active mine sites and an acidophilic bacterium,carries functions able to cope with the extreme conditions,whereas Latescibacteria specific in abandoned sites can degrade organics,as well the iron/sulfide metabolism genera.The tailings sites became extremely acidic(pH?2)during nature attenuation.As well,the acid soluble fraction of metal(loid)s,representing the leachable fraction,was generally higher in the 31 years old abandoned tailing sites(content of As reached 29.3 mg kg-1).Desul.furivibrio,which were always coupled with sulfur/sulfide reduction to dissimilate the reduction of nitrate/nitrite,were specific in tailings with 3 years of abandonment.However,genus beneficial to plant growth(Rhizobium),and iron/sulfur-oxidizing bacteria and metal(loid)-related genera(Acidiferrobacter and Acidithiobacillus)were specific within tailings abandoned for 23 years or more.The tailings had low microbial activities using microcalorimetry,and had Pmax values ranging from 64 to 330?W.The spatial distribution characteristics of bacterial community are mainly as follows:distribution of bacterial communities was found stability at horizontal levels.At the surface(depth of 0-10 cm),the stability was most attributed to Bacillus and Enterococcus,while bacterial communities at subsurface(50 cm)were mainly contributed by Nitrospira and Sul.furicella.Variable vertical distribution of bacterial communities led to the occurrence of specific genus and specific predicted functions.Sulfurifustis(S-oxidizing and inorganic carbon fixing bacteria)was specific at the surface,while Streptococcus related genera were found at the subsurface.The total content of metal(loid),such as Cr,Cu,Fe,Mn and Pb tended to decrease during biotreatment.The solidified rates of these metal(loid)s were above 94%in the surface,which were lower than that in the subsurface.The proportion of four metal(loid)s species were mainly found in the residual fraction.The decreased of mineral metallic oxide and appearance of metallic sulfide,such as ZnS indicated that the added microbial consortium could contribute to the transformation of metal(loid)s into stable sulfide minerals.The added microbial consortium,especially Desul.fotomaculum genus showed a high relative abundance(12%),which could co-evolution with indigenous flora to increase the microbial activity and abundance of tailings.In addition,the presence of genes involved in sulfate reduction,including CysH,AprAB,SUOX,and TST,indicated that the consortium play an important role in the transformation of metal(loid)s.In summary,the In Situ mineralization technique could effectively solidify metal(loid)s of tailings,and increase the immobility of all the researched metal(loid)s,which was helpful to have a good prevention and control of tailings.Present study could provide theoretical basis and technical supports for the development and utilization of functional microorganisms for in-situ mineralization bio-treatment. |
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