Acid Mine Drainage Environments Research Articles

New Insights into Microbial Interactions with Dissolved Organic Matter in Acid Mine Drainage with the Integration of Microbial Community and Chemical Composition Analysis

Acid mine drainage (AMD) environments are one of the most extreme ecosystems on earth, and their biogeochemical cycling has been widely studied. However, the carbon cycling underlying microbial interactions with dissolved organic matter (DOM) is poorly understood in these environments. Here, we evaluated the relationships between microbial populations and DOM pools in an AMD lake by combining high-throughput microbial and chemical compositional analyses. The results demonstrated that microalgae were the predominant primary producers in the system and significantly contributed to the total DOM concentration in the water column, whereas DOM chemodiversity was correlated with bacterial community diversity. Network analyses further revealed that DOM associated with microalgae had low diversity but high relative abundance, suggesting microalgal selective organic matter contribution to the DOM pool. Conversely, diverse DOM molecules with generally low abundance were associated with heterotrophic acidophiles, including members of Alphaproteobacteria, Actinobacteria, Firmicutes, and Acidobacteria. Moreover, microalgae and bacteria exhibited predominantly positive co-occurrences with potential metabolic interactions via DOM exchange. Taken together, this study provides new insights into the microbe–DOM interactions in extreme AMD ecosystems and has significant implications for understanding the carbon cycle and microbial metabolism in extreme environments.

Correlations Between Root Metabolomics and Bacterial Community Structures in the Phragmites australis Under Acid Mine Drainage-Polluted Wetland Ecosystem

Despite root microecology playing critical role in plant growth and fidelity, relatively few studies have focused on the link between the microbial communities and root metabolome in the aquatic macrophytes under heavy metal (HM) pollution. Using high-throughput metagenomic sequencing, targeted metabolomics and community-level physiological profile analyses, we investigated the symbiotic associations between Phragmites australis with rhizospheric bacterial communities under differing acid mine drainage (AMD) pollution. Results indicated that AMD pollution and root localization significantly affected root metabolome profiles. Higher accumulation of adenosine monophosphate, inosine, methionine, carnitine and dimethylglycine were observed in the rhizosphere under AMD than non-AMD habitat. Overall, the bacterial diversity and richness, and functional (metabolic) diversity were lower under high-AMD pollution. While non-AMD site was enriched with members of phylum Firmicutes, Proteobacteria were the most abundant taxa in the rhizosphere and endosphere under AMD-polluted sites. Further, plant growth promoting rhizobacteria (Rhizobium, Delftia, Bradyrhizobium, and Mesorhizobium) and metal-tolerant bacteria (Bacillus, Arthrobacter, Massilia and Methylocystis) were most abundant in AMD-polluted than non-AMD habitat. Finally, pH, TDS (total dissolved solids), Cu, Cr, Fe, and Zn content were the key environmental factors that strongly contributed to the spatial perturbation of rhizospheric metabolites, proteobacterial and acidobacterial taxa. Overall, the study linked the differential endospheric and rhizospheric bacterial community and metabolite profiles in P. australis under AMD environment and provided insights into HM adaptability and phytoremediation potential.

Key Factors Governing Microbial Community in Extremely Acidic Mine Drainage (pH

The microbial community of acid mine drainage (AMD) fascinates researchers by their adaption and roles in shaping the environment. Molecular surveys have recently helped to enhance the understanding of the distribution, adaption strategy, and ecological function of microbial communities in extreme AMD environments. However, the interactions between the environment and microbial community of extremely acidic AMD (pH <3) from different mining areas kept unanswered questions. Here, we measured physicochemical parameters and profiled the microbial community of AMD collected from four mining areas with different mineral types to provide a better understanding of biogeochemical processes within the extremely acidic water environment. The prominent physicochemical differences across the four mining areas were in SO42−, metal ions, and temperature, and distinct microbial diversity and community assemblages were also discovered in these areas. Mg2+ and SO42− were the predominant factors determining the microbial structure and prevalence of dominant taxa in AMD. Leptospirillum, Ferroplasma, and Acidithiobacillus were abundant but showed different occurrence patterns in AMD from different mining areas. More diverse communities and functional redundancy were identified in AMD of polymetallic mining areas compared with AMD of copper mining areas. Functional prediction revealed iron, sulfur, nitrogen, and carbon metabolisms driven by microorganisms were significantly correlated with Mg2+ and SO42−, Ca2+, temperature, and Fe2+, which distinguish microbial communities of copper mine AMD from that of polymetallic mine AMD. In summary, microbial diversity, composition, and metabolic potential were mainly shaped by Mg2+ and SO42− concentrations of AMD, suggesting that the substrate concentrations may contribute to the distinct microbiological profiles of AMD from different mining areas. These findings highlight the microbial community structure in extremely acidic AMD forming by types of minerals and the interactions of physicochemical parameters and microbiology, providing more clues of the microbial ecological function and adaptation mechanisms in the extremely acidic environment.

Physiological, Genomic and Transcriptomic Analyses Reveal the Adaptation Mechanisms of Acidiella bohemica to Extreme Acid Mine Drainage Environments.

Fungi in acid mine drainage (AMD) environments are of great concern due to their potentials of decomposing organic carbon, absorbing heavy metals and reducing AMD acidity. Based on morphological analysis and ITS/18S high-throughput sequencing technology, previous studies have provided deep insights into the diversity and community composition of fungi in AMD environments. However, knowledge about physiology, metabolic potential and transcriptome profiles of fungi inhabiting AMD environments is still scarce. Here, we reported the physiological, genomic, and transcriptomic characterization of Acidiella bohemica SYSU C17045 to improve our understanding of the physiological, genomic, and transcriptomic mechanisms underlying fungal adaptation to AMD environments. A. bohemica was isolated from an AMD environment, which has been proved to be an acidophilic fungus in this study. The surface of A. bohemica cultured in AMD solutions was covered with a large number of minerals such as jarosite. We thus inferred that the A. bohemica might have the potential of biologically induced mineralization. Taking advantage of PacBio single-molecule real-time sequencing, we obtained the high-quality genome sequences of A. bohemica (50 Mbp). To our knowledge, this was the first attempt to employ a third-generation sequencing technology to explore the genomic traits of fungi isolated from AMD environments. Moreover, our transcriptomic analysis revealed that a series of genes in the A. bohemica genome were related to its metabolic pathways of C, N, S, and Fe as well as its adaptation mechanisms, including the response to acid stress and the resistance to heavy metals. Overall, our physiological, genomic, and transcriptomic data provide a foundation for understanding the metabolic potential and adaptation mechanisms of fungi in AMD environments.

Metagenome-Assembled Genomes of Novel Taxa from an Acid Mine Drainage Environment.

ABSTRACTAcid mine drainage (AMD) is a global problem in which iron sulfide minerals oxidize and generate acidic, metal-rich water. Bioremediation relies on understanding how microbial communities inhabiting an AMD site contribute to biogeochemical cycling. A number of studies have reported community composition in AMD sites from 16S rRNA gene amplicons, but it remains difficult to link taxa to function, especially in the absence of closely related cultured species or those with published genomes. Unfortunately, there is a paucity of genomes and cultured taxa from AMD environments. Here, we report 29 novel metagenome-assembled genomes from Cabin Branch, an AMD site in the Daniel Boone National Forest, Kentucky, USA. The genomes span 11 bacterial phyla and one archaeal phylum and include taxa that contribute to carbon, nitrogen, sulfur, and iron cycling. These data reveal overlooked taxa that contribute to carbon fixation in AMD sites as well as uncharacterized Fe(II)-oxidizing bacteria. These data provide additional context for 16S rRNA gene studies, add to our understanding of the taxa involved in biogeochemical cycling in AMD environments, and can inform bioremediation strategies.IMPORTANCE Bioremediating acid mine drainage requires understanding how microbial communities influence geochemical cycling of iron and sulfur and biologically important elements such as carbon and nitrogen. Research in this area has provided an abundance of 16S rRNA gene amplicon data. However, linking these data to metabolisms is difficult because many AMD taxa are uncultured or lack published genomes. Here, we present metagenome-assembled genomes from 29 novel AMD taxa and detail their metabolic potential. These data provide information on AMD taxa that could be important for bioremediation strategies, including taxa that are involved in cycling iron, sulfur, carbon, and nitrogen.

The Stratified Distribution of Dissolved Organic Matter in an AMD Lake Revealed by Multi-sample Evaluation Procedure.

As a typical extreme environment, acid mine drainage (AMD) has been extensively studied for its biogeochemical cycle, but little is known about the quality of dissolved organic matter (DOM) in AMD. In this study, DOM molecules in an AMD lake were detected with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and the change of DOM molecules in the stratified water column was analyzed with a multi-sample evaluation procedure. The results demonstrate that DOM quality is highly stratified and can be linked with severe biogeochemical gradients. In the surface layer, DOM molecules can be distinguished by low quantities and intensities, as well as potential photodegradation products. Oxygen-poor and oxygen-rich molecules alternately dominate the chemocline, which can be explained by the redox-dependent adsorption/desorption of DOM on metastable secondary minerals. A rich and abundant DOM pool with a high proportion of heteroatoms exists at the bottom which can be significantly influenced by material exchange with sediments. These findings emphasize the active role of DOM in extreme AMD environments and expand the understanding of the carbon cycle in the hydrosphere.

Reductive dissolution of Pb-Zn jarosite under near-neutral conditions

Jarosite, an oxyhydroxysulfate secondary mineral, exists widely in mining areas, typically in association with heavy metals, such as Pb or Zn. Replacement by heavy metals at different sites within the jarosite crystal structure may lead to change in its dissolution behavior. Fe(II) can significantly catalyze jarosite dissolution–recrystallization under near-neutral conditions in reductive soil or sediment systems. However, it has been unclear whether the reductive dissolution characteristics, and the end products of bimetallic–replaced Pb-Zn jarosite, were similar to those of other jarosite–type minerals (such as As(V)–bearing jarosite). In this study, the dynamics of aqueous and solid parameters were combined to analyze liberation of Pb2+, Zn2+ and SO42− from Pb-Zn jarosite, in 0, 1, and 10 mM Fe(II) systems. We found that in all the systems, the Pb2+, Zn2+, and SO₄2− release percentages exhibited two liberation stages, which appeared to be mainly due to the formation of secondary phases. In the fast stage, which occurred within 1 d, the Pb2+, Zn2+, and SO₄2−, liberation speeds ranked in the order of SO42− > Pb2+ > Zn2+, while in slower liberation stage, which occurred after 1 d, the liberation speeds ranked in the order of Pb2+ > Zn2+ > SO42−, and on the whole, the liberation priority ranked in the order of SO42− > Pb2+ > Zn2+. Examination using X–ray powder diffraction, Raman spectroscopy, scanning electron microscopy, and X–ray photoelectron spectroscopy revealed that lepidocrocite was the only detectable secondary product in the low Fe(II) system, while lepidocrocite and goethite, together with amorphous anglesite, formed in the high Fe(II) system. The author considers that this study sheds light on predicting the environmental fates of trace elements associated with acid mine drainage environments, while providing a basic concept, together with useful information, for heavy metal remediation in mining areas.

Mobile genetic elements mediate the mixotrophic evolution of novel Alicyclobacillus species for acid mine drainage adaptation.

Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR-Cas systems, but had more GI, IS, and ICE, as well as more MGE-associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions.

Fungal and metabolome diversity of the rhizosphere and endosphere of Phragmites australis in an AMD-polluted environment

Symbiotic associations with rhizospheric microbial communities coupled with the production of metabolites are key adaptive mechanisms by metallophytes to overcome metal stress. However, little is known about pseudometallophyte Phragmites australis interactions with fungal community despite commonly being applied in wetland phytoremediation of acid mine drainage (AMD). In this study, fungal community diversity and metabolomes production by rhizosphere and root endosphere of P. australis growing under three different AMD pollution gradient were analyzed. Our results highlight the following: 1) Ascomycota and Basidiomycota were dominant phyla, but the diversity and richness of taxa were lower within AMD sites with Penicillium, Candida, Saccharomycetales, Vishniacozyma, Trichoderma, Didymellaceae, and Cladosporium being enriched in the root endosphere and rhizosphere in AMD sites than non-AMD site; 2) non-metric multidimensional scaling (NMDS) of 73 metabolomes revealed spatially defined metabolite exudation by distinct root parts (rhizosphere vs endosphere) rather than AMD sites, with significant variability occurring within the rhizosphere correlating to pH, TDS, Fe, Cr, Cu and Zn content changes; 3) canonical correspondence analysis (CCA) confirmed specific rhizospheric fungal taxonomic changes are driven by pH, TDS, heavy metals, and stress-related metabolomes produced. This is the first report that gives a snapshot on the complex endophytic and rhizospheric fungal community structure and metabolites perturbations that may be key in the adaptability and metal phytoremediation by P. australis under AMD environment.

Thermoplasmata and Nitrososphaeria as dominant archaeal members in acid mine drainage sediment of Malanjkhand Copper Project, India.

Acid mine drainage (AMD) harbors all three life forms inspite of its toxic and hazardous nature. In comparison to bacterial diversity, an in-depth understanding of the archaeal diversity in AMD and their ecological significance remain less explored. Archaeal populations are known to play significant roles in various biogeochemical cycles within the AMD ecosystem, and it is imperative to have a deeper understanding of archaeal diversity and their functional potential in AMD system. The present study is aimed to understand the archaeal diversity of an AMD sediment of Malanjkhand Copper Project, India through archaea specific V6 region of 16S rRNA gene amplicon sequencing. Geochemical data confirmed the acidic, toxic, heavy metal-rich nature of the sample. Archaea specific V6-16S rRNA gene amplicon data showed a predominance of Thermoplasmata (BSLdp215, uncultured Thermoplasmata, and Thermoplasmataceae) and Nitrososphaeria (Nitrosotaleaceae) members constituting ~ 95% of the archaeal community. Uncultured members of Bathyarchaeia, Group 1.1c, Hydrothermarchaeota, and Methanomassiliicoccales along with Methanobacteriaceae, Methanocellaceae, Haloferaceae, Methanosaetaceae, and Methanoregulaceae constituted the part of rare taxa. Analysis of sequence reads indicated that apart from their close ecological relevance, members of the Thermoplasmata present in Malanjkhand AMD were mostly involved in chemoheterotrophy, Fe/S redox cycling, and with heavy metal resistance, while the Nitrososphaeria members were responsible for ammonia oxidation and fixation of HCO3- through 3-hydroxypropionate/4-hydroxybutyrate cycle at low pH and oligotrophic environment which subsequently played an important role in nitrification process in AMD sediment. Overall, the present study elucidated the biogeochemical significance of archaeal populations inhabiting the toxic AMD environment.

Metabolic Diversity and Evolutionary History of the Archaeal Phylum "Candidatus Micrarchaeota" Uncovered from a Freshwater Lake Metagenome.

Acidophilic archaea of the archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) group from the uncultured candidate phylum "Candidatus Micrarchaeota" have small genomes and cell sizes and are known to be metabolically dependent and physically associated with their Thermoplasmatales hosts. However, phylogenetically diverse "Ca Micrarchaeota" are widely distributed in various nonacidic environments, and it remains uncertain because of the lack of complete genomes whether they are also devoted to a partner-dependent lifestyle. Here, we obtained nine metagenome-assembled genomes of "Ca Micrarchaeota" from the sediments of a meromictic freshwater lake, including a complete, closed 1.2 Mbp genome of "Ca Micrarchaeota" Sv326, an archaeon phylogenetically distant from the ARMAN lineage. Genome analysis revealed that, contrary to ARMAN "Ca Micrarchaeota," the Sv326 archaeon has complete glycolytic pathways and ATP generation mechanisms in substrate phosphorylation reactions, the capacities to utilize some sugars and amino acids as substrates, and pathways for de novo nucleotide biosynthesis but lacked an aerobic respiratory chain. We suppose that Sv326 is a free-living scavenger rather than an obligate parasite/symbiont. Comparative analysis of "Ca Micrarchaeota" genomes representing different order-level divisions indicated that evolution of the "Ca Micrarchaeota" from a free-living "Candidatus Diapherotrites"-like ancestor involved losses of important metabolic pathways in different lineages and gains of specific functions in the course of adaptation to a partner-dependent lifestyle and specific environmental conditions. The ARMAN group represents the most pronounced case of genome reduction and gene loss, while the Sv326 lineage appeared to be rather close to the ancestral state of the "Ca Micrarchaeota" in terms of metabolic potential.IMPORTANCE The recently described superphylum DPANN includes several phyla of uncultivated archaea with small cell sizes, reduced genomes, and limited metabolic capabilities. One of these phyla, "Ca Micrarchaeota," comprises an enigmatic group of archaea found in acid mine drainage environments, the archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) group. Analysis of their reduced genomes revealed the absence of key metabolic pathways consistent with their partner-associated lifestyle, and physical associations of ARMAN cells with their hosts were documented. However, "Ca Micrarchaeota" include several lineages besides the ARMAN group found in nonacidic environments, and none of them have been characterized. Here, we report a complete genome of "Ca Micrarchaeota" from a non-ARMAN lineage. Analysis of this genome revealed the presence of metabolic capacities lost in ARMAN genomes that could enable a free-living lifestyle. These results expand our understanding of genetic diversity, lifestyle, and evolution of "Ca Micrarchaeota."

Arsenic behavior during gallic acid-induced redox transformation of jarosite under acidic conditions

Jarosite is an important scavenger for arsenic (As) due to its strong adsorption capacity and ability to co-precipitate metal(loid)s in acid mine drainage (AMD) environments. When subjected to natural organic matter (NOM), metastable jarosite may undergo dissolution and transformation, affecting the mobility behavior of As. Therefore, the present study systematically explored the dissolution and transformation of jarosite, and the consequent redistribution of coprecipitated As(V) under anoxic condition in the presence of a common phenolic acid–gallic acid (GA). The results suggested that As(V) incorporating into the jarosite structure stabilized the mineral and inhibited the dissolution process. Jarosite persisted as the dominant mineral phase at pH 2.5 up to 60 d, though a large amount of structural Fe(III) was reduced by GA. However, at pH 5.5, jarosite mainly transformed to ferrohexahydrite (FeSO4·6H2O) with GA addition, while the principal end-product was goethite in GA-free system. The dissolution process enhanced As(V) mobilization into aqueous and surface-complexed phase at pH 2.5, while co-precipitated fraction of As(V) remained dominant under pH 5.5 condition. Result of XPS indicated that no reduction of As(V) occurred during the interaction between GA and As(V)-bearing jarosite, which would limit the toxicity to the environment. The reductive process involved that GA promoted the dissolution of jarosite via the synergistic effect of ligand and reduction, following by GA and release As(V) competing for active sites on mineral surface. The findings demonstrated that phenolic groups in NOM can exert great influence on the stability of jarosite and partitioning behavior of As(V).

Sulfide mineral bioleaching: Understanding of microbe-chemistry assisted hydrometallurgy technology and acid mine drainage environment protection

Bioleaching is regarded as an essential technology to treat low grade minerals, with the distinctive superiorities of lower-cost and environment-friendly compared with traditional pyrometallurgy method. However, the bioleaching efficiency is unsatisfactory owing to the passivation film formed on the minerals surface. It is of particular interest to know the dissolution and passivation mechanism of sulfide minerals in the presence of microorganism. Although bioleaching can be useful in extracting metals, it is a double-edged sword. Metallurgical activities have caused serious environmental problems such as acid mine drainage (AMD). The understanding of some common sulfide minerals bioleaching processes and protection of Amd environment is reviewed in this article.

Shallow floating treatment wetland capable of sulfate reduction in acid mine drainage impacted waters in a northern climate

Floating treatment wetlands (FTW)s that can uptake nutrients and metals from water, and/or trap suspended solids in their roots, are becoming viable options to treat urban, agriculture and sewage runoffs. However, current FTW designs favor aerobic processes and short-term storage of metals, which are ineffective in acid mine drainage (AMD) environments. Many also function poorly in northern latitudes with strong seasonality and several months of sub-zero temperatures. In this study, we designed a novel FTWs with 20 cm soil profile to test its ability to sustain anaerobic microbial processes, such as iron and sulfate reduction and remain functional after freezing conditions of winter months. Three different plants, Carex lacustris, Typha latifolia, and Juncus canadensis were used to test in our FTWs, which were deployed in a mining-impacted water in Sudbury, ON, Canada. Porewater samples were acquired using built-in porewater peepers. Low to moderately reducing conditions, along with presence of ferrous iron and hydrogen sulfide in the porewater of all FTWs was prevalent, irrespective of the constituent vegetation type. Moreover, as well as a ~30% increase in sulfate-reducing bacteria (SRB) richness and ~100% increase in SRB abundance between years, was the evidence that anaerobic processes were occurring in these shallow FTWs. From this study we estimated that during its lifetime, one shallow FTW can treat ~61 m3 of sulfate-rich water, thus offering an alternative way to capture sulfate and other metals from mining-impacted waters.

Sulfate Reduction for Bioremediation of AMD Facilitated by an Indigenous Acidand Metal-Tolerant Sulfate-Reducer.

Acid mine drainage (AMD) has been a serious environmental issue that threatens soil and aquatic ecosystems. In this study, an acid-tolerant sulfate-reducing bacterium, strain S4, was isolated from the mud of an AMD storage pond in Vietnam via enrichment in anoxic mineral medium at pH 5. Comparative analyses of sequences of the 16S rRNA gene and dsrB gene involved in sulfate reduction revealed that the isolate belonged to the genus Desulfovibrio, and is most closely related to Desulfovibrio oxamicus (with 99% homology in 16S rDNA sequence and 98% homology in dsrB gene sequence). Denaturing gradient gel electrophoresis (DGGE) analyses of dsrB gene showed that strain S4 represented one of the two most abundant groups developed in the enrichment culture. Notably, strain S4 was capable of reducing sulfate in low pH environments (from 2 and above), and resistance to extremely high concentration of heavy metals (Fe 3,000 mg/l, Zn 100 mg/l, Cu 100 mg/ l). In a batch incubation experiment in synthetic AMD with pH 3.5, strain S4 showed strong effects in facilitating growth of a neutrophilic, metal sensitive Desulfovibrio sp. strain SR4H, which was not capable of growing alone in such an environment. Thus, it is postulated that under extreme conditions such as an AMD environment, acid- and metal-tolerant sulfate-reducing bacteria (SRB)- like strain S4 would facilitate the growth of other widely distributed SRB by starting to reduce sulfate at low pH, thus increasing pH and lowering the metal concentration in the environment. Owing to such unique physiological characteristics, strain S4 shows great potential for application in sustainable remediation of AMD.

Effect of ferric ions on the anaerobic bio-dissolution of jarosites by Acidithiobacillus ferrooxidans

Large amounts of jarosites are produced during zinc hydrometallurgy and bioleaching, as well as in acid sulfate soils and acid mine drainage environments. As such, understanding the behavior of jarosite dissolution is important for analyzing the iron cycle process and promoting the control and treatment of jarosites. In general, soluble ferric ions and jarosites coexist in acid environments; however, the relationship between soluble ferric ions and jarosites under anaerobic reductive conditions is still not well understood. In this study, the effect of adding Fe3+ on the promotion of the bio-dissolution of jarosites using Acidithiobacillus ferrooxidans is investigated. With the addition of 12 mM Fe3+, the efficiency and maximum rate of jarosite bio-dissolution were found to reach 84.1% and 2.66 mmol/(L·d), respectively. The addition of Fe3+ at concentrations higher than 12 mM did not further improve the jarosite bio-dissolution. These results indicate that the mechanisms underlying these improvements include: (i) the reduction of the zeta potential due to the compression of the diffusion layer of the electric double layer by Fe3+; (ii) bacteria growth enhancement and the stabilization of the pH of cultures via the reduction of soluble Fe3+. Based on these observations, this study serves to promote the development of jarosite bio-dissolution using Acidithiobacillus ferrooxidans and challenges the idea that soluble Fe3+ suppresses the bio-dissolution reaction of solid Fe3+ substances such as jarosite when soluble ferric ions and jarosite coexist.

Microbial community structure and function in acid mine drainage from Mengzi, Yunnan Province

In order to explore the microbial communities and functions in distinct environments of acid mine drainage (AMD) ecosystem and fully comprehend the patterns of AMD formation and development, high-throughput sequencing technology was used to study the prokaryotic community composition in AMD puddles and surrounding rills in a mining area in Mengzi, Yunnan Province, China. By combining with physicochemical properties of the samples, we distinguished the key factors affecting the community structure and analyzed the environmental functions of the microflora. We discovered that the main phyla in AMD puddles were Euryarchaeota, Proteobacteria (including the class α-, γ- and δ-Proteobacteria), Nitrospirae, Firmicutes, Actinobacteria, and Acidobacteria. Community structure of the AMD puddles apparently differed from that of the surrounding rills. Microbial diversity was significantly positively correlated with pH, whereas the relative abundance of Thermoplasmata was negatively correlated with pH and this class might play a predominant role in community structure. There was high relative abundance of the genus Ferroplasma (6.60%-86.34%) in different samples of AMD puddles. Acidithiobacillus spp. were the major iron- and/or sulfur-oxidizing bacteria in AMD solutions and sediments, whereas relative abundance of the obligate iron-oxidizer Leptospirillum spp. was lower, and Ferrovum spp. were almost only present in the AMD solutions. In addition, acidophilic or acid-tolerant heterotrophic bacteria were widely distributed in the AMD solutions and sediments, which might promote the growth of iron- and/or sulfur-oxidizers and catalyze the oxidative/reductive dissolution of metal ores. Our results suggested that pH significantly impacted the microbial community structure of AMD environment by affecting the microbial diversity and microflora distribution.

Acid Mine Drainage as Habitats for Distinct Microbiomes: Current Knowledge in the Era of Molecular and Omic Technologies.

The last decade has witnessed growth in scientific interest towards studying the biodiversity and ecology in extreme environments. Acid Mine Drainage (AMD), formed through the bio-oxidation of metal sulphides, is a typical extreme environment that is inhospitable to most life forms. Through the application of traditional culture-based molecular techniques, it has been established that AMD is home to a low diversity, specialized and novel microbial community that plays a critical role in its formation. Intensive efforts have been channeled towards understanding the ecology, microbial biodiversity, processes and metabolic networks within these simple ecosystems. Molecular techniques using high-throughput next-generation sequencing platforms have taken center stage in discerning both the taxonomic and functional diversity in these microbial communities. Recently developed post-genomic approaches as well have been particularly instrumental in deciphering in situ interactions within microbial communities and the environment. In this review, a critical synopsis of the current applications of advanced molecular techniques in probing microbial and functional diversity in AMD environments is presented.

Characterization of a pH-Tolerant Strain Cobetia sp. SASS1 and Its Phenol Degradation Performance Under Salinity Condition.

Biological treatment of complex saline phenolic wastewater remains a great challenge due to the low activity of bacterial populations under stressful conditions. Acid mine drainage (AMD) as a typically extreme environment, shaped unique AMD microbial communities. Microorganisms survived in the AMD environment have evolved various mechanisms of resistance to low pH, high salinity and toxic heavy metals. The primary goal of this work was to determine whether a strain isolated from an AMD could degrade phenol under stressful conditions such as low pH, high salinity and heavy metals. The results suggested that the strain Cobetia sp. SASS1 isolated from AMD presented different physiological characteristics in comparison with five most closely related species. SASS1 can efficiently degrade phenol at wide ranges of pH (3.0–9.0) and NaCl concentration (0–40 g/L), as well as the existence of Cu2+ and Mn2+. Specifically, the SASS1 could completely degrade 1500 mg/L phenol in 80 h at 10 g/L NaCl. Meanwhile, mineralization of phenol was achieved with complete degradation of 900 mg/L phenol and simultaneously COD decreasing from 2239 mg/L to 181.6 mg/L in 36 h. Based on biodegradation metabolites identification and enzyme activities analysis, both ortho-cleavage pathway and benzoic acid pathway for phenol degradation were proposed. These findings suggested that SASS1 was an efficient phenol degrader under salinity and acidic conditions, and could be considered as key population for bioremediation of industrial phenolic wastewaters under stressful conditions.

Solid and Aqueous Speciation of Yttrium in Passive Remediation Systems of Acid Mine Drainage.

Yttrium belongs to the rare earth elements (REEs) together with lanthanides and scandium. REEs are commonly used in modern technologies, and their limited supply has made it necessary to look for new alternative resources. Acid mine drainage (AMD) is a potential resource since it is moderately enriched in REEs. In fact, in passive remediation systems, which are implemented to minimize the environmental impacts of AMD, REEs are mainly retained in basaluminite, an aluminum hydroxysulfate precipitate. In this study, the solid and liquid speciation and the local structure of yttrium are studied in high-sulfate aqueous solutions, basaluminite standards, and samples from remediation columns using synchrotron-based techniques and molecular modeling. Pair distribution function (PDF) analyses and ab initio molecular dynamics density functional theory models of the yttrium sulfate solution show that the YSO4+ ion pair forms a monodentate inner-sphere complex. Extended X-ray absorption fine structure (EXAFS) and PDF analyses show that Y is retained by basaluminite, forming a monodentate inner-sphere surface complex on the aluminum hydroxide surface. EXAFS of the column samples shows that more than 72% of their signal is represented by the signal of basaluminite with which YSO4+ forms an inner-sphere complex. The atomic view of the REE configuration in AMD environments could facilitate a deeper research of REE recovery from waste generated in AMD remediation systems.