•V(V) reduction coupled to PHE degradation is realized under anaerobic condition.•250-d continuous column experiment implies the influences of hydrochemical factors.•V(V) is reduced to V(IV) and PHE ...is degraded into small molecule organics.•Functional microbes, genes, catalytic compounds and secretions are analyzed.
Vanadate V(V) and phenanthrene (PHE) commonly coexist in groundwater aquifer, posing potential threats to ecological environment and public health. However, little is known about the complicated biogeochemical processes involving microbial V(V) reduction coupled with co-metabolic PHE biodegradation. Herein we demonstrated that synchronous removal of V(V) and PHE could be realized under anaerobic condition. Complete V(V) removal and PHE degradation efficiency of 82.0 ± 0.8% were achieved in 7-d operation in batch experiment. 250-d continuous column experiment implied that hydrochemical condition affected V(V) and PHE removals. V(V) was reduced to insoluble vanadium (IV) and PHE was degraded into small molecule organics (e.g. salicylic acid). Geobacter and Acetobacterium used methanol and intermediates from PHE degradation as electron donors for V(V) reduction. PHE was decomposed by Mycobacterium and Clostridium with methanol as co-metabolic substrate and V(V) as electron acceptor. Genes encoding proteins for V(V) reduction (omcA, omcB and mtrC) and PHE degradation (phnAc) were upregulated. Cytochrome c and nicotinamide adenine dinucleotide promoted electron transfer for V(V) and PHE detoxification. Extracellular polymeric substances could bind V(V) and improve the bioavailability of PHE. Our findings provide a robust strategy for remediation of V(V) and PHE co-contaminated groundwater.
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Rhizosphere microorganisms play important roles in plant health and growth. The diversity and composition of rhizosphere microbial communities have been well studied, but little is known about their ...co-occurrence patterns, especially at a continental scale. Herein, we performed a network-based analysis using integrated bacterial and fungal community datasets to delineate the co-occurrence patterns of bulk soil and rhizosphere microbiome and the geographic patterns of network topological features in 51 soybean fields across China. Results showed that the microbial networks differed between bulk soil and rhizosphere in terms of structure and composition. Compared with the bulk soil networks, the rhizosphere networks had fewer links between bacteria and fungi, lower modularity, and smaller average path length; the global, southern and northern networks of rhizosphere showed similar, higher and lower complexity, respectively. The southern-specific networks of both bulk soil and soybean rhizosphere had more links between bacteria and fungi compared with the northern-specific networks. Additionally, the geographic patterns of network topological features differed between bulk soil and rhizosphere habitats, northern and southern regions. Bacterial sub-networks of both bulk soil and rhizosphere were most influenced by soil pH; fungal sub-networks were related to fewer environmental factors and most influenced by soil Mg content. Given that microbial networks may reflect interactions or niches shared among microorganisms, these results provide new insights into the organization of rhizosphere microbial communities.
•We compared bulk soil and rhizosphere microbial networks at a continental scale.•The rhizosphere networks had fewer bacteria-fungi links than the bulk soil networks.•Soil pH was the strongest predictor of bacterial sub-networks topological features.•Soil Mg was the strongest predictor of fungal sub-networks topological features.
Organic matter and reduced sulfur compounds commonly coexist in groundwater aquifers and their respective roles in Cr(VI) bio-reduction have been well established, but Cr(VI) bio-reduction under ...mixotrophic condition, where organics and elemental sulfur simultaneously occur as co-donors of electrons, remains largely unknown. Herein a sulfur-based mixotrophic bio-reduction process is demonstrated to be effective to detoxify Cr(VI), with a removal efficiency of 95.5 ± 0.74% within 48 h at an initial concentration of 50 mg/L. In addition to direct reduction by heterotrophic Cr(VI) reducers such as Desulfovibrio and Desulfuromonas, volatile fatty acids (VFAs) produced from autotrophic sulfur oxidation served as electron donors for heterotrophic Cr(VI) reducers. Part of VFAs was also assimilated and accumulated as glycogen within cells, which enhanced their Cr(VI) removal capacity. Metabolic pathway analysis suggested that Cr(VI) was reduced to insoluble Cr(III) both extracellularly by cytochrome c and intracellularly by nicotinamide adenine dinucleotide in the presence of upregulated chrA gene. Constituents of extracellular polymeric substances (EPS) also contributed to Cr(VI) reduction enzymatically, through binding of toxic Cr(VI) by carboxyl and hydroxyl groups. Results from this study have important implications for understanding the biogeochemical behavior and environmental remediation of Cr(VI) in groundwater aquifers and sediments/soils.
Advanced oxidation processes decompose heavy metal complexes.
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Heavy metal complexes with high mobility are widely distributed in wastewater from modern industries, which are more ...stable and refractory than free heavy metal ions. Their removals from wastewater draw increasing attentions and various technologies have been developed, among which advanced oxidation processes (AOPs) are more effectively and promising. Progresses on five representative types of AOPs, including Fenton (like) oxidation, electrochemical oxidation, photocatalytic oxidation, ozonation and discharge plasma oxidation for heavy metal complexes degradation are summarized in this review. Their rationales, advantages, applications, challenges and prospects are introduced independently. Combinations among these AOPs, such as electrochemical Fenton oxidation and photoelectrocatalytic oxidation, are also comprehensively highlighted. Future efforts should be made to reduce acid requirement and scale up for practical applications of AOPs for heavy metal complex degradation efficiently and cost-effectively.
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•V(V) and Cr(VI) are simultaneously reduced in a autotrophic S(0)-based biosystem.•Cr(VI) is reduced preferentially, while reduction of V(V) is easily inhabited.•Reactive products of ...V(V), Cr(VI) and S(0) are V(IV), Cr(III) and sulfate in turn.•Carbon isotope and microbial analyses reveal the synergetic mechanisms.
Vanadium and chromium co-exist commonly with elevated levels in groundwater at vanadium smelting sites. While bioremediation has been recognized promising for this co-contamination treatment in aquifer, interactions during vanadium (V) V(V) and chromium (VI) Cr(VI) bio-reductions under autotrophic condition remain largely unknown. In this study, efficient reductions of V(V) and Cr(VI) from synthetic groundwater were realized simultaneously in a continuous flow autotrophic sulfur-based biosystem, with more than 85% overall removals under hydrochemical and hydrodynamic fluctuations during 276-d operation. Soluble Cr(VI) was reduced to insoluble Cr(III) preferentially, while reduction of soluble V(V) to insoluble V(IV) was easily inhibited. Elemental sulfur S(0) was bio-oxidized to sulfate. Analyses of carbon isotope, microbial community and metabolic pathway revealed the synergetic mechanisms. Autotrophs (e.g., Sulfuricurvum) utilized energy released from S(0) oxidation to synthesize volatile fatty acids (VFAs), which were consumed by heterotrophic V(V) and/or Cr(VI) reducers (e.g., Geobacter). Functional genes responsible for S(0) oxidation and reduction of V(V) and Cr(VI) were detected. V(V) and Cr(VI) reductions were catalyzed by both cytochrome c and nicotinamide adenine dinucleotide. VFAs were also transformed to glycogen in cells to store energy. Robust remediation strategy is thereby proposed for aquifer co-contaminated by V(V) and Cr(VI).
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•Smelting plants cause heavy vanadium pollution in local area.•Vanadium pollution posed serious impact on soil microbes over multiple gradients.•Vanadium(V)-reducing related bacteria ...might play a core role in community response.•Relation between vanadium(V)-reducing related bacteria and vanadium was explored.
The mining and smelting of navajoite has resulted in a serious vanadium pollution in regional geological environments and significant influence on soil microorganisms. However, the core microbiome responsible for adjusting community response to vanadium pollution and the driving pattern have been kept unclear. In this study, a suite of surface and profile soil samples over multiple gradients were collected in four directions and distances of 10–2000 m from a vanadium smelting plant in Panzhihua, China. The indigenous microbial communities and vanadium(V)-reducing related bacteria (VRB) were profiled by 16S rRNA gene high-throughput sequencing technique. Five VRB were detected in the original collected soil samples including Bacillus, Geobacter, Clostridium, Pseudomonas and Comamonadaceae based on high-throughput sequencing data analysis, and their abundances were significantly related with the content of vanadium. Low vanadium concentration promoted the growth of VRB, while high vanadium concentration would inhibit VRB multiplication. The Gaussian equation could be used to quantitatively describe the nonlinear relationship between VRB and vanadium. Network analysis demonstrated that the microbial communities were significantly influenced by VRB assemblage, and 1.32–52.77% of microbes in the community showed a close association with VRB. A laboratory incubation experiment also confirmed the core role of VRB to drive community response to vanadium pressure.
•Nanosized hydrous zirconium oxide (HZrO) is decorated on anion exchange resin D201.•HZrO@D201 exhibits outstanding selective V(V) adsorption with co-existing anions.•Adsorption thermodynamics and ...adsorption kinetics are systematically studied.•HZrO@D201 indicates a satisfactory lifespan in column experiment for V(V) removal.
Adsorption is widely used in removal of toxic vanadium (V) V(V) from water streams, and a fit-for-purpose adsorbent plays a vital role in this process. Herein HZrO@D201, an adsorbent with decoration of nanosized hydrous zirconium oxide (HZrO) on anion exchange resin D201, is fabricated for efficient V(V) removal. Compared to pristine D201, HZrO@D201 excelled in V(V) removal with a maximum adsorption capacity of 118.1 mg/g, due to potential formation of inner sphere complexation between V(V) and HZrO. HZrO@D201 could also functioned well in a wide pH range (3.00 to 9.00) and exhibited outstanding selective V(V) adsorption under the presence of competing anions (chloride, nitrate, sulfate, and phosphate). The adsorption thermodynamics was in accordance with the Langmuir model, while adsorption kinetics followed the Pseudo-Second-Order model. When treating actual vanadium contaminated groundwater from Panzhihua region (China), HZrO@D201 indicated a satisfactory lifespan in the column experiment for V(V) removal (2.41 times longer than D201), and the treated groundwater could meet the vanadium standard of drinking water source in China (less than 50 μg/L). Regeneration of HZrO@D201 was easily achievable with negligible capacity loss. Results from this work suggests a promising application potential of HZrO@D201 in vanadium pollution control.
Fungi play a crucial role in the agroecological system; however, little is known about their large-scale biogeographical patterns and how various ecological processes contribute to community ...assembly, especially in the crop rhizosphere. In this study, we investigated the spatial distribution and community assembly of fungi in the bulk soil and rhizosphere of soybean collected from 43 sites across China using high-throughput sequencing. The alpha diversity of the rhizosphere was lower than that of bulk soil. The fungal community structures of the two soil compartments were distinct. Fungal communities in the rhizosphere had a steeper distance-decay relationship slope between sampled sites than those in bulk soil, suggesting a greater influence of historical processes (geographical separation) in the rhizosphere. The relative importance of dispersal limitation and environmental filtering for the fungal community composition differed between bulk soil and rhizosphere. Sloan neutral model analysis suggested that niche-based processes dominated the assemblage of fungal communities in the two soil compartments, while neutral processes had a weaker influence in the rhizosphere than in bulk soil. Additionally, we analyzed the structures of abundant and rare fungal sub-communities in each soil compartment. Rare sub-communities were more strongly influenced by dispersal limitation than abundant sub-communities. These results expand the current understanding of root-associated fungal community biogeography in agricultural soils on a large scale.
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•Root-associated fungi of soybean were studied on a larger scale in China by High–throughput sequencing.•Rhizosphere and bulk soil harbored distinct fungal community compositions.•Fungal communities in rhizosphere had a steeper distance-decay relationship slope than those in the bulk soil.•Niche-based processes were found to have a stronger influence in the rhizosphere than in bulk soil.•Distinct biogeography patterns were observed in root-associated abundant and rare fungal sub-communities.
Vanadium (V) pollution in groundwater has posed serious risks to the environment and public health. Anaerobic microbial reduction can achieve efficient and cost-effective remediation of V(V) ...pollution, but its interactions with coexisting common electron acceptors such as NO3−, Fe3+, SO42− and CO2 in groundwater remain unknown. In this study, the interactions between V(V) reduction and reduction of common electron acceptors were examined with revealing relevant microbial community and identifying dominant species. The results showed that the presence of NO3− slowed down the removal of V(V) in the early stage of the reaction but eventually led to a similar reduction efficiency (90.0% ± 0.4% in 72-h operation) to that in the reactor without NO3−. The addition of Fe3+, SO42−, or CO2 decreased the efficiency of V(V) reduction. Furthermore, the microbial reduction of these coexisting electron acceptors was also adversely affected by the presence of V(V). The addition of V(V) as well as the extra dose of Fe3+, SO42− and CO2 decreased microbial diversity and evenness, whereas the reactor supplied with NO3− showed the increased diversity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the accumulation of Geobacter, Longilinea, Syntrophobacter, Spirochaeta and Anaerolinea, which might be responsible for the reduction of multiple electron acceptors. The findings of this study have demonstrated the feasibility of anaerobic bioremediation of V(V) and the possible influence of coexisting electron acceptors commonly found in groundwater.
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•Interaction of microbial V(V) reduction with other electron acceptors is studied.•NO3− slows V(V) reduction first but eventually has a minor effect.•Fe3+, SO42−, CO2 decreases V(V) reduction with different inhibition effects.•Geochemical reduction of these electron acceptors is adversely affected by V(V).•Microbial diversity, evenness and functional species are revealed.
The presence of multiple electron acceptors can reduce the efficiency of microbial reduction of Vanadium. The dominant species in microbial community have been identified.
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•Fe(II)-bearing minerals can support Cr(VI) bio-reduction in groundwater.•Mackinawite performs best in Cr(VI) removal.•Groundwater chemistry and hydrodynamics influence the ...process.•Biotic and abiotic contributions to Cr(VI) reduction are quantified.•Synergistic mechanisms between microbial consortia are revealed.
To date, comparatively little is known about the role of natural Fe(II)-bearing minerals in bioremediation of chromium (VI) contaminated aquifers subject to chemoautotrophic conditions. This work employed four kinds of Fe(II)-bearing minerals (pyrite, mackinawite, wustite, and magnetite) as inorganic electron donors to support Cr(VI) bio-reduction. In batch experiments, mackinawite (FeS) performed best, with Cr(VI) removal efficiency of 98.1 ± 1.21 % in 96 h. Continuous column experiments lasting 180 d implied that groundwater chemistry and hydrodynamics influenced the Cr(VI) removal process. A breakthrough study suggested that biotic and abiotic contributions to Cr(VI) reduction were 76.0 ± 1.12 % and 24.1 ± 1.43 %, respectively. Cr(VI) was reduced to insoluble Cr(III), whereas Fe(II) and S(-II) in mackinawite were finally oxidized to Fe(III) and sulfate. Mackinawite evolved progressively into pyrrhotite. High-throughput 16S rRNA gene sequencing indicated that mackinawite-driven Cr(VI) reduction was mediated through synergistic interactions of microbial consortia; i.e. autotrophs as Acidovorax synthesized volatile fatty acids as metabolic intermediates, which were consumed by Cr(VI) reducers as Geobacter. Genes encoding enzymes for S oxidation (soxB) and Cr(VI) reduction (chrA, yieF) were upregulated. Cytochrome c participating in Fe(II) oxidation increased significantly. This work advances the development of sustainable techniques for Cr(VI) polluted groundwater remediation.
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