Novel Pathway for Vanadium(V) Bio-Detoxification by Gram-Positive Lactococcus raffinolactis

Influence pathways of vanadium stress to microbial community in soil-tailings-groundwater systems

The large-scale exploitation of vanadium (V) bearing minerals has led to a massive accumulation of V tailings, of which V pollution poses severe ecological risks. Although the mechanisms of V stress to the microbial community have been reported, the influential pathways in a multi-medium-containing system, for example, the soil-tailings-groundwater system, are unknown. The dynamic redox conditions and substance exchange within the system exhibited complex V stress on the local microbial communities. In this study, the influence pathways of V stress to the microbial community in the soil-tailings-groundwater system were first investigated. High V contents were observed in groundwater (139.2 ± 0.15 µg/L) and soil (98.0-323.8 ± 0.02 mg/kg), respectively. Distinct microbial composition was observed for soil and groundwater, where soil showed the highest level of diversity and richness. Firmicutes, Proteobacteria, Actinobacteria, and Acidobacteria were dominant in soil and groundwater with a sum relative abundance of around 80 %. Based on redundancy analysis and structural equation models, V was one of the vital driving factors affecting microbial communities. Groundwater microbial communities were influenced by V via Cr, dissolved oxygen, and total nitrogen, while Fe, Mn, and total phosphorus were the key mediators for V to affect soil microbial communities. V affected the microbial community via metabolic pathways related to carbonaceous matter, which was involved in the establishment of survival strategies for metal stress. This study provides novel insights into the influence pathways of V on the microorganisms in tailings reservoir for pollution bioremediation.

Natural mackinawite-based elimination of vanadium and ammonium from wastewater in autotrophic biosystem

Vanadium (V) production results in significant amounts of wastewater, which often co-contains considerable ammonium (NH4+) after being used as precipitants. Both pentavalent V [V(V)] and NH4+ can be removed independently through biological process. However, internal interactive biotechnology for one-step elimination of V(V) and NH4+ remains an enigma. In this study, we proposed biologically removing V(V) and NH4+ simultaneously with natural mineral mackinawite as electron donor and its oxidation products as electron acceptors. Our bioreactor achieved a V(V) removal efficiency of 99.5 ± 0.22 % and an NH4+-N removal capacity of 49.5 ± 0.40 g/m3·d. V(V) was reduced to tetravalent V precipitates, while mackinawite was bio-oxidized to Fe(III) and sulfate. Metagenomic binning analysis indicated Sulfurivermis sp. mediated mackinawite oxidation and V(V) reduction. Putative Pseudomonas sp. conducted NH4+ assimilation, anaerobic ammonium oxidation coupled to Fe(III) reduction (Feammox), and denitrification, achieving complete NH4+-N removal. Real-time qPCR validated the upregulation of functional genes involved in V(V) reduction and nitrogen metabolisms, with improved functional enzyme activities. Cytochrome c, nicotinamide adenine dinucleotide, and extracellular polymeric substances promoted electron transfer, facilitating the elimination of both V(V) and NH4+-N from wastewater. This study offers a novel and sustainable biological strategy for one-step treating V industrial wastewater.

In-situ bioremediation of vanadium contaminated soil using volatile fatty acids obtained from fruit and vegetable waste

Fatty acids (VFAs) that obtained from organic waste are environmentally friendly and readily available soil amendments that could enhance the bioremediation efficiency of vanadium (V)-contaminated soils. This study aimed to clarify the in-situ immobilization mechanisms of VFAs for actual V-contaminated soils in mining areas, and investigated the effects of varying concentrations of VFA application on the valence state, existing forms, bioavailability, and toxicity of V in soils, as well as the changes in plant growth, V uptake, and abundances of microbial species and their metal resistance genes. The findings revealed that the water-extractability, bioavailability, toxicity, and acid-soluble (F1) fractions of V reduced by up to 52.8%, 51.0%, 46.9%, and 81.7%, whereas the oxidizable (F3) and residual (F4) fractions increased by a factor of up to 3.1 and 1.1, following VFA addition. Consequently, the stem height of Setaria viridis increased by a factor of 4.5, and the reduction in V accumulation in shoots and roots were reached up to 95.4% and 67%. The VFA-induced soil pH decrement, along with the enhancement of soil organic matter content and the proliferation of Proteobacteria and its arsenic reduction genes, were the key factors influencing environmental behavior and biochemistry of V in contaminated soils.

This work investigated the effects of various concentrations of biomass derived VFAs on the bioavailability, mobility, toxicity and fractionation of V in contaminated soils, and elucidated their immobilization mechanisms. The reduction in soil pH, along with the increase in soil OM and AP content, are the primary abiotic factors influencing the valence state, bioavailability, and toxicity of vanadium in contaminated soils, whereas the enhancement of the abundances of Proteobacteria and their arsenic reduction genes represent the major biotic factors affecting these properties.

Synchronous vanadium bio-reduction/detoxification/recovery and nitrogen attenuation in a membrane aerated biofilm reactor

The presence of both pentavalent vanadium [V(Ⅴ)] and nitrogen in wastewaters from vanadium smelting poses significant environmental challenges. However, it remains little in the way of continuous flow biological reactor to concurrently eliminated V(Ⅴ) and nitrogen in wastewaters. Herein, membrane-aerated biofilm reactor (MABR) system was designed to achieve simultaneous nitrification and denitrification (SND) alongside biological reduction, detoxification, and recovery of vanadium. Vanadium and nitrogen removal performances, solid-state characterization, microbial compositions and functional genes, and the mechanism related to the metabolism of vanadium and nitrogen were illuminated. Notably, we identified a potential role for biofilm-derived "secretion" in the transformation of V(Ⅴ) and nitrogen. Our findings revealed that the system achieved SND efficiency of 98.00 ± 0.57 % and removed 91.10 ± 3.60 % of total vanadium (TV) even at high influent V(Ⅴ) concentrations in continuous flow stage. Batch experiments implied that the conversion of NH4+-N was the limiting process of nitrogen removal in MABR system, and the extracellular polymeric substances (EPS) might play an important role in the conversion of V(Ⅴ) and nitrogen. V(Ⅴ) was reduced to V(Ⅳ), which was immobilized to biofilm and "secretion" by microbial surface functional groups, including C-O, O-C=O and -OH. Acinetobacter, Dechlorobacter, Denitratisoma and Nitrospira were verified as microbes associated with V(Ⅴ) and nitrogen metabolism. The abundance of functional genes pertaining to electron donor, electron transport, and electron acceptor systems increased under high V(V) stimulation. Collectively, the cooperation of biofilm and "secretion" ensured the intensive removal of vanadium and nitrogen. This study provides new insights into the concurrent removal of heavy metal and environmental nutrient.

Remediation of vanadium(V)-contaminated groundwater by the Shewanella oneidensis MR-1, Fe2O3, and biochar composite

Vanadium, essential for steel production and energy storage, is increasingly found in groundwater due to extensive mining and industrial activities. Its high mobility and reactivity pose significant environmental risks. This study developed an Shewanella oneidensis MR-1- Fe2O3-biochar composite to enhance vanadium bioremediation. The composite exhibited strong vanadium resistance, achieving 92.5 ± 1.48% removal of pentavalent vanadium [V(V)] at 100 mg/l with an optimal biochar/Fe₂O₃ ratio of 10:1. Its efficiency was further assessed under varying pH, organic carbon levels, and V(V) concentrations. XPS analysis confirmed the presence of tetravalent vanadium [V (IV)] and divalent iron [Fe (II)], while FTIR spectroscopy identified functional groups (-OH, C=C, C=O) within the composite. These results suggest a synergistic removal mechanism involving complexation, dissimilatory iron reduction, and microbial V(V) reduction. This study provides a promising strategy for remediating V(V)-contaminated groundwater. PRACTITIONER POINTS: A novel composite consisted of Shewanella oneidensis MR-1, Fe2O3, and biochar was synthesized Complex promoted microbial life and increased resistance towards V(V) Complexation, Fe (II) oxidation, and bioreduction collectively contributed to V(V) removal.

Photoheterotrophic extracellular reduction of ferrihydrite activates diverse intracellular metabolic pathways in Rhodopseudomonas palustris for enhanced antibiotic degradation

Anoxygenic photosynthetic bacteria (APB) have been frequently detected as a photoautotrophic Fe-carbon cycling drivers in photic and anoxic environment. However, the potential capacity of these bacteria for photoheterotrophic extracellular reduction of iron-containing minerals and their impact on the transformation of organic pollutants remain currently unknown. This study investigated the capacity of R. palustris, a purple non-sulfur anoxygenic photosynthetic bacterium, to reduce ferrihydrite (Fh) and its correlation with sulfamethazine (SDZ) degradation were firstly investigated. The results revealed that R. palustris could undergo photoheterotrophic extracellular reduction of Fh to form goethite through direct contact, facilitating the formation of conductive bands and enter the interior of cells with a maximum Fe(II)/Fe(T) ratio of up to 39 % within 8 days which led to 13 % increase in assimilation rate of acetate carbon and 53.2 % increase in SDZ degradation rates, as compared with those by R. palustris alone. Moreover, the intermediates generated during the degradation of SDZ by R. palustris-Fh exhibited relatively lower developmental toxicity compared with the original SDZ molecule. The extracellular reduction of Fh significantly up-regulated the expression of genes related to photosynthetic metabolic enzymes, extracellular electron transporters, and extracellular degrading enzymes in R. palustris. This enhancement promoted the photoheterotrophic metabolism and extracellular secretion of photosensitive active compounds in R. palustris, thereby enhancing both the biodegradation and photosensitive degradation of SDZ.

Insights into the hydrogen-fueled bioreduction of vanadium(V) by marine Shewanella sp. FDA-1: Process and mechanism

Microbial-driven V(V) reduction plays a crucial role in its biogeochemical cycle, yet the mechanisms underlying this bioreduction remain inadequately understood. While the effectiveness of organic compounds as electron donors in facilitating bacterial reduction of V(V) has been established, the role of inorganic electron donors in initiating this process at the level of pure cultured bacteria has not been explored. In this study, we report on a marine Shewanella sp. FDA-1 that utilizes hydrogen (H2) as an energy source to reduce V(V). In addition, the reduction mechanism was investigated through a combination of genomics, RT-qPCR, heterologous expression of key proteins, extracellular secretion analyses, and electron transfer activity assays. Our results demonstrate that H2 serves as an effective electron donor, enabling Shewanella sp. FDA-1 to reduce V(V) across various salinities (2-7 %) and pH values (5-9). When exposed to 5 mM V(V), the presence of 1-20 mL of H2 resulted in V(V) bioreduction rates ranging from 0.039 to 0.11 h-1 (R2 > 0.73). Amorphous V(IV) compounds were characterized as reduction products using XRD, XPS, FTIR, and SEM. Mechanistic studies indicate that the glutathione system, cytochromes, and extracellular substances such as riboflavin play important roles in V(V) reduction (p < 0.05). Furthermore, our findings reveal that the addition of H2 and lactate triggers different response sequences among these three reduction pathways, suggesting distinct reduction mechanisms between organic and inorganic electron donors. These insights enhance our understanding of microbial vanadium transformation and provide valuable guidance for developing novel H2-based remediation technologies for vanadium-contaminated environments.

Vanadate reduction by gram-positive fermentative bacteria isolated from deep-sea sediments on the northern Central Indian Ridge

The oxidation states of vanadium determine its mobility and toxicity, and dissimilatory vanadate reduction has been reported in several microorganisms, highlighting the potential significance of this pathway in the remediation of vanadium contamination and the biogeochemical cycle. However, to date, most known microorganisms capable of reducing vanadate are Gram-negative respiratory bacteria belonging to the phylum Proteobacteria. In this study, we isolated Tepidibacter mesophilus strain VROV1 from deep-sea sediments on the northern Central Indian Ridge and investigated its ability to reduce vanadium and the impact of vanadate on its cellular metabolism. A series of culture experiments revealed that the isolated strain efficiently reduces V(V) to V(IV) during fermentation, even at mM levels, and this reduction involves a direct biological process rather than indirect reduction via metabolic products. Vanadium affects microbial carbon and nitrogen metabolism. Notably, in the presence of vanadate, alanine production decreases, suggesting that metabolic flux is diverted from the transamination reaction to vanadate reduction. T. mesophilus VROV1 is the second Gram-positive bacterium identified to reduce vanadium, following Lactococcus raffinolactis, but these bacteria belong to different classes: T. mesophilus is classified as Clostridia, whereas L. raffinolactis is classified as Bacilli. The specific rate of vanadate removal by VROV1 was as high as 2.8 pmol/cell/day, which is comparable to that of metal-reducing bacteria and markedly exceeds that of L. raffinolactis. Our findings expand the distribution of vanadate-reducing organisms within the bacterial domain. Given the wide range of natural habitats of T. mesophilus and its close relatives, we speculate that fermentative vanadate reduction may have a greater impact on the global biogeochemical cycle of vanadium than previously thought.

Overlooked roles of improved substrates functions in remodeling microbial community and driving metabolic traits during sludge fermentation triggered by surfactants and antibiotics co-existence

Sludge anaerobic fermentation is a pivotal route to transit wastewater treatment plants towards energy-neutral and resource recovery-oriented plants, while the overall efficiency is commonly restrained by co-exist contaminants. This study unveiled the cooperative effect of sulfadiazine (SDZ) and linear alkylbenzene sulfonates (LAS) in driving volatile fatty acids (VFAs) biosynthesis during waste activated sludge (WAS) anaerobic fermentation. The VFAs remarkably elevated to 1189 mg COD/L in LAS/SDZ, which was approximately 1.3-3.2 folds of SDZ and LAS. SDZ and LAS synergistically disintegrated extracellular polymeric substances to provide fermentation substrates. These changes altered microbial population and enhanced microbial networks interconnection. Moreover, the proteins released from WAS might facilitate electron transfer among microorganisms. The functional anaerobic species, including hydrolytic-acidogenic bacteria (e.g., Veillonellaceae and Lactobacillus) and electroactive bacteria (e.g., Parabacteroides and Fonticella), were enriched. Also, the metabolic traits responsible for transmembrane transport, intracellular metabolism, VFAs biosynthesis and electron transfer-related process were strengthened with the upregulation of functional genes. Further analysis revealed that the functional anaerobic species activated quorum sensing and two-component systems to counteract unfavorable LAS/SDZ stress and maintain high metabolic activities. This work elucidated the overlooked roles of substrates in modulating anaerobic consortia and metabolic traits in sludge fermentation systems with mixed pollutants stressing.

Fe(III) reduction mediates vanadium release and reduction in vanadium contaminated paddy soil under different organic amendments

Vanadium(V) contaminated soil is abundant in iron(Fe) oxides due to co-occurrence of V and Fe bearing minerals. However, biogeochemical transformation of redox-active V and Fe in soil, and the bacteria involved, has remained less investigated. This study explored the extent to which microbial mediated organic decomposition coupled to Fe(III) reduction contributed to V(V) release/reduction in V-contaminated paddy soil under different organic amendments. Soil flooding decreased toxic reducible V while increased less toxic oxidizable V. Glucose and straw promoted V(V) release with temporarily increasing V(V) concentration by 73.59-106.34 mg/kg compared to the control treatment and subsequently promoted V(V) reduction with decreasing V(V) to concentrations eventually similar to the control treatment. Biochar incorporation under glucose and straw amendments moderately alleviated V(V) release. The significantly positive correlation between Fe(II) and V(V) concentrations during the V solubilization process indicated a temporal coupling of Fe(III) reduction and V(V) release. Clostridium and Massilia mediated Fe(III) reductive dissolution and V(V) release, while Anaeromyxobacter, Sphingomonas, Bryobacter, Acidobacteriaceae and Anaerolineaceae contributed to V(V) reduction. This study provides a deeper understanding of V biotransformation coupled to Fe and C cycling and suggests a remediation strategy for V-contaminated soils via regulating Fe(III) reduction to weaken V(V) release or to promote V(V) reduction.

Vanadium (V) reduction and the performance of electroactive biofilms in microbial fuel cells with Shewanella putrefaciens

The electron transfer ability of biofilms significantly influences the electrochemical activity of microbial fuel cells (MFCs). However, there is limited understanding of pentavalent vanadium (V(V)) bioreduction and microbial response characteristics in MFCs. In this study, the effect of gradient concentrations of V(V) on the performance of EABs with Shewanella putrefaciens in MFCs was investigated. The results showed that as V(V) concentration increased (0-100 mg/L), the voltage output, power densities, polarization, and electrode potential decreased. V(V) was found to act as an electron acceptor and was reduced during MFCs operation, with a yield of 83.16% being observed at 25 mg/L V(V). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicated declining electrochemical performance of the MFCs with escalating V(V) concentration. The content of protein and polysaccharide from extracellular polymeric substances (EPS) in anodic biofilms increased to 66.75 and 49.15 mg/L at 75 mg/L V(V), respectively. Three-dimensional fluorescence spectroscopy confirmed increased humic substances in EPS extraction with V(V) exposure. The functional genes narG, nirK, and gor involved in V(V) reduction were upregulated with rising V(V) concentration through quantitative polymerase chain reaction (qPCR) analysis. Additionally, riboflavin, cytochrome c, nicotinamide adenine dinucleotide (NADH), and electron transport system activity (ETSA), key indicators for assessing electron transfer behavior, exhibited a negative correlation with various V(V) concentrations, decreasing by 31.81%, 57.14%, 67.39%, and 51.41%, respectively, at a concentration of 100 mg/L V(V) compared to the blank control. These findings contribute valuable insights into the response of EABs to V(V) exposure, presenting potential strategies for enhancing their effectiveness in the treatment of vanadium-contaminated wastewater.

Distinguishing contributions of diverse sediment components to vanadium transport, immobilization and transformation in aquifer

Vanadium (V) occurs in environment naturally and anthropogenically, but little has been understood about its environmental behavior in groundwater aquifer with sediments. This study investigated the pentavalent V [V(V)] transport and transformation under the influence of different sediment components (minerals, organic matter, and microorganisms) through column experiments. All these components played pivotal roles in V immobilization. The synergistic effects of sediment components enhanced V retention compared to individual component. Mineral components, particularly those containing carbonates and metal oxides, predominantly influenced V(V) transport as indicated by XRD analysis. Organic matter, especially under low pH conditions, induced particle aggregation, thereby inhibiting the transport of V(V). The V K-edge X-ray absorption near-edge structure spectroscopy revealed the formation of tetravalent V[V(IV)] in treatments involving organic matter and microorganisms. Notably, organic matter exhibited the capability to directly reduce V(V). The introduction of microorganisms restricted V(V) transfer. V(V) reducing genera (e.g., Brevundimonas, Arenimonas, Xanthobacter) were detected, achieving V(V) reduction to insoluble V(IV). V(V) bioreduction was improved by minerals that promote microbial metabolism with enhanced electron transfer, or by organic matter that increases levels of intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances. This study specifies the contributions of different sediment components to the transportation and transformation of V, deepening our understanding of V biogeochemistry in groundwater aquifer.

Electric stimulation mitigated the mixed microplastic inhibition to anaerobic digestion during wastewater treatment

The presence of mixed microplastics (MPs) in anaerobic wastewater treatment processes has been shown to impede fermentation performance by suppressing microbial activity. Microbial electrosynthesis (MES), with its extensive potential, offers a promising solution for refractory substances management and methane recovery, achieved through the enhancement of microbial metabolism and interspecies electron transfer. This study, therefore, delves into the functional impacts and the microbial response to MES in the remediation of wastewater contaminated with mixed-MPs. Results indicated that mixed-MPs could inhibit methane production (-52.38%) and substance removal (-26.59%), and MES could effectively mitigate this inhibitory effect (-22.86%, -19.01%). Concurrently, MES also boosts enzymatic activities pivotal for electron transfer, such as cytochrome c and nicotinamide adenine dinucleotide (NADH), as well as those linked to energy metabolism like adenosine triphosphate (ATP). Furthermore, MES bolsters microbial resistance to mixed-MPs, as evidenced by an increase in extracellular polymeric substances (EPS), albeit with a minor rise in reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release. Correspondingly, electric stimulation promoted the enrichment of functional microorganisms associated with fermentation, acetate production, electrogenesis, and methanogenesis, and stimulated elevated expression levels of genes related to methane metabolism. Notably, the Methanothrix-mediated acetoclastic pathway emerges as the predominant methanogenic route, succeeded by the Methanobacterium-driven hydrogenotrophic pathway. Lastly, the study underscores the supportive role of applied voltage and carriers in energy metabolism and substance transport, which are associated with methanogenesis. Overall, MES demonstrates efficacy in mitigating the biotoxicity induced by mixed-MPs exposure and in enhancing anaerobic wastewater treatment and methane recovery.

Multiple pathways of vanadate reduction and denitrification mediated by denitrifying bacterium Acidovorax sp. strain BoFeN1

Contamination of aquifers by a combination of vanadate [V(V)] and nitrate (NO3-) is widespread nowadays. Although bioremediation of V(V)- and nitrate-contaminated environments is possible, only a limited number of functional species have been identified to date. The present study demonstrates the effectiveness of V(V) reduction and denitrification by a denitrifying bacterium Acidovorax sp. strain BoFeN1. The V(V) removal efficiency was 76.5 ± 5.41 % during 120 h incubation, with complete removal of NO3- within 48 h. Inhibitor experiments confirmed the involvement of electron transport substances and denitrifying enzymes in the bioreduction of V(V) and NO3-. Cyt c and riboflavin were important for extracellular V(V) reduction, with quinone and EPS more significant for NO3- removal. Intracellular reductive compounds including glutathione and NADH directly reduce V(V) and NO3-. Reverse transcription quantitative PCR confirmed the important roles of nirK and napA genes in regulating V(V) reduction and denitrification. Bioaugmentation by strain BoFeN1 increased V(V) and NO3- removal efficiency by 55.3 % ± 2.78 % and 42.1 % ± 1.04 % for samples from a contaminated aquifer. This study proposes new microbial resources for the bioremediation of V(V) and NO3-contaminated aquifers, and contributes to our understanding of coupled vanadium, nitrogen, and carbon biogeochemical processes.

Seasonal and Spatial Fluctuations of Reactive Oxygen Species in Riparian Soils and Their Contributions on Organic Carbon Mineralization

Reactive oxygen species (ROS) are ubiquitous in the natural environment and play a pivotal role in biogeochemical processes. However, the spatiotemporal distribution and production mechanisms of ROS in riparian soil remain unknown. Herein, we performed uninterrupted monitoring to investigate the variation of ROS at different soil sites of the Weihe River riparian zone throughout the year. Fluorescence imaging and quantitative analysis clearly showed the production and spatiotemporal variation of ROS in riparian soils. The concentration of superoxide (O2•-) was 300% higher in summer and autumn compared to that in other seasons, while the highest concentrations of 539.7 and 20.12 μmol kg-1 were observed in winter for hydrogen peroxide (H2O2) and hydroxyl radicals (•OH), respectively. Spatially, ROS production in riparian soils gradually decreased along with the stream. The results of the structural equation and random forest model indicated that meteorological conditions and soil physicochemical properties were primary drivers mediating the seasonal and spatial variations in ROS production, respectively. The generated •OH significantly induced the abiotic mineralization of organic carbon, contributing to 17.5-26.4% of CO2 efflux. The obtained information highlighted riparian zones as pervasive yet previously underestimated hotspots for ROS production, which may have non-negligible implications for carbon turnover and other elemental cycles in riparian soils.

Improving vanadium removal from contaminated river water in constructed wetlands: The role of arbuscular mycorrhizal fungi

Industrial activities pose a significant ecological risk to water resources as they pollute surrounding waters with vanadium (V). Although the contribution of plants and substrates to V removal in constructed wetlands (CWs) has been reported, the role of arbuscular mycorrhizal fungi (AMF) is unclear. The aim of the present study was to investigate the role of AMF in V removal in CWs and to elucidate the underlying mechanisms. Reed plants (Phragmites australis) were inoculated with an AMF strain (Rhizophagus irregularis) in CW columns, creating AMF-inoculated (+AMF) and non-inoculated (-AMF) treatments. Three levels of influent V concentrations (low: 0.50 mg L-1, medium: 1.14 mg L-1 and high: 1.52 mg L-1) were examined. The + AMF treatment showed higher V removal (60%-98%) than the control (40%-82%) in all three conditions, although the difference was not significant in some cases. The mean mycorrhizal effects were 75%, 19%, and 28% for low, moderate, and high influent V concentrations, respectively. The +AMF treatment showed a higher GRSP-bonded V concentration (5.5 mg g-1) than the -AMF treatment (4.0 mg g-1). Furthermore, +AMF treatment showed larger plants with higher V concentrations in their tissues, accompanied by increased biological concentration factors and biological accumulation factors. Given the remarkable positive effect of AMF on V removal, our study suggests that treating AMF in CWs is a worthwhile approach.

Community assembly and microbial interactions in an alkaline vanadium tailing pond

Intensive development of vanadium-titanium mines leads to an increasing discharge of vanadium (V) into the environment, imposing potential risks to both environmental system and public health. Microorganisms play a key role in the biogeochemical cycling of V, influencing its transformation and distribution. In addition, the characterization of microbial community patterns serves to assess potential threats imposed by elevated V exposure. However, the impact of V on microbial community remains largely unknown in alkaline V tailing areas with a substantial amounts of V accumulation and nutrient-poor conditions. This study aims to explore the characteristics of microbial community in a wet tailing pond nearby a large-scale V mine. The results reveal V contamination in both water (0.60 mg/L) and sediment tailings (340 mg/kg) in the tailing pond. Microbial community diversity shows distinctive pattern between environmental metrices. Genera with the functional potential of metal reduction\resistance, nitrogen metabolism, and carbon fixation have been identified. In this alkaline V tailing pond, V and pH are major drivers to induce community variation, particularly for functional bacteria. Stochastic processes primarily govern the assemblies of microbial community in the water samples, while deterministic process regulate the community assemblies of sediment tailings. Moreover, the co-occurrence network pattern unveils strong selective pattern for sediment tailings communities, where genera form a complex network structure exhibiting strong competition for limited resource. These findings reveal the patterns of microbial adaptions in wet vanadium tailing ponds, providing insightful guidelines to mitigate the negative impact of V tailing and develop sustainable management for mine-waste reservoir.

Vanadium Accumulation and Reduction by Vanadium-Accumulating Bacteria Isolated from the Intestinal Contents of Ciona robusta

The sea squirt Ciona robusta (formerly Ciona intestinalis type A) has been the subject of many interdisciplinary studies. Known as a vanadium-rich ascidian, C. robusta is an ideal model for exploring microbes associated with the ascidian and the roles of these microbes in vanadium accumulation and reduction. In this study, we discovered two bacterial strains that accumulate large amounts of vanadium, CD2-88 and CD2-102, which belong to the genera Pseudoalteromonas and Vibrio, respectively. The growth medium composition impacted vanadium uptake. Furthermore, pH was also an important factor in the accumulation and localization of vanadium. Most of the vanadium(V) accumulated by these bacteria was converted to less toxic vanadium(IV). Our results provide insights into vanadium accumulation and reduction by bacteria isolated from the ascidian C. robusta to further study the relations between ascidians and microbes and their possible applications for bioremediation or biomineralization.

Toxicity of VO2 micro/nanoparticles to nitrogen-fixing bacterium Azotobacter vinelandii

Vanadium dioxide (VO2) has been used in a variety of products due to its outstanding phase transition properties. However, as potential heavy metal contaminants, the environmental hazards and risks of VO2 should be systematically investigated. Biological nitrogen fixation is one of the most dominant processes in biogeochemical cycle, which is associated with nitrogen-fixing bacteria. In this study, we reported the environmental bio-effects of VO2 micro/nanoparticles on the nitrogen-fixing bacterium Azotobacter vinelandii. VO2 at 10 and 30 mg/L caused severe hazards to A. vinelandii, such as cell apoptosis, oxidative damage, physical damage, genotoxicity, and the loss of nitrogen fixation activity. The up-regulated differentially expressed genes of A. vinelandii were related to stress response, and the down-regulated genes were mainly related to energy metabolism. Surprisingly, VO2 of 10 mg/L decreased the nif gene expression but elevated the vnf gene expression, which enhanced the ability of A. vinelandii to reduce acetylene in anaerobic environment. In addition, under tested conditions, VO2 nanoparticles exhibited insignificantly higher toxicity than VO2 microparticles.

Insight into characteristics of sulphur-based autotrophic denitrifying microbiota in the nitrate removal

Mariculture wastewater is characterized by low organic carbon to nitrogen ratio (C/N) but high nitrate concentration, which makes it difficult to remove nitrate by the completely heterotrophic denitrification. However, high nitrate discharge poses a threat to the natural environment and human health. Thus, we enriched sulphur-based autotrophic denitrifying (SAD) microbiota and optimized the nitrate removal under different environmental factors and electron donor conditions. The results showed that the dominant genera in the enriched microbiota were previously confirmed autotrophic denitrifiers, Sulfurovum, Thioalkalispira-Sulfurivermis, and Sedimenticola, with a high relative abundance of 41.14%, 21.01%, and 6.17%. Among the environmental factors, pH was the key factor affecting SAD microbiota, and pH 7-9 favoured nitrate removal. However, high pH led to nitrite accumulation (e.g. 10 mg/L at pH = 9), which should be strictly avoided. With regard to electron donors, the optimal concentrations of thiosulphate and nitrate were 50 and 5 mg/L, respectively. The best organic carbon is acetate with an optimal concentration of 10 mg/L. Meanwhile, the initial concentration of thiosulphate was proportional to the nitrate removal rate, while higher concentrations of organic carbon stimulated the heterotrophic denitrification potential of microbiota and thus benefited to dentrification. This study showed that the enriched SAD microbiota was able to achieve efficient nitrate removal under suitable environmental conditions and mixed electron donors and thus presented the potential for application in the treatment of mariculture wastewater.

Nodulation Signaling Pathway 1 and 2 Modulate Vanadium Accumulation and Tolerance of Legumes

Vanadium (V) pollution potentially threatens human health. Here, it is found that nsp1 and nsp2, Rhizobium symbiosis defective mutants of Medicago truncatula, are sensitive to V. Concentrations of phosphorus (P), iron (Fe), and sulfur (S) with V are negatively correlated in the shoots of wild-type R108, but not in mutant nsp1 and nsp2 shoots. Mutations in the P transporter PHT1, PHO1, and VPT families, Fe transporter IRT1, and S transporter SULTR1/3/4 family confer varying degrees of V tolerance on plants. Among these gene families, MtPT1, MtZIP6, MtZIP9, and MtSULTR1; 1 in R108 roots are significantly inhibited by V stress, while MtPHO1; 2, MtVPT2, and MtVPT3 are significantly induced. Overexpression of Arabidopsis thaliana VPT1 or M. truncatula MtVPT3 increases plant V tolerance. However, the response of these genes to V is weakened in nsp1 or nsp2 and influenced by soil microorganisms. Mutations in NSPs reduce rhizobacterial diversity under V stress and simplify the V-responsive operational taxonomic unit modules in co-occurrence networks. Furthermore, R108 recruits more beneficial rhizobacteria related to V, P, Fe, and S than does nsp1 or nsp2. Thus, NSPs can modulate the accumulation and tolerance of legumes to V through P, Fe, and S transporters, ion homeostasis, and rhizobacterial community responses.

Pyrrhotite-dependent microbial reduction and magnetic separation for efficient vanadium detoxification and recovery in contaminated aquifer

Microbial reduction under anaerobic condition is a promising method for remediating vanadate [V(V)] contamination in aquifers, while V(V) may be re-generated with redox fluctuations. The inability to remove vanadium after remediation has become a key issue limiting bioremediation. In this study, we proposed the use of pyrrhotite, a natural mineral with magnetic properties, to immobilize V(V) to insoluble V(IV) under microbial action and remove vanadium from the aquifer using a magnetic field, which could avoid the problem of V(V) recontamination under redox fluctuating conditions. Up to 49.0 ± 4.7 % of vanadium could be removed from the aquifer by the applied magnetic field, and the vanadium in the aquifer after the reaction was mainly in the acid-extractable and reducible states. pH had a strong effect on the magnetic recovery of V(V), while the influence of initial V(V) concentration was weak. Microbial community structure analysis showed that Thiobacillus, Proteiniphilum, Fermentimonas, and Desulfurivibrio played key roles for V(V) reduction and pyrrhotite oxidation. Structural equation model indicated the positive correlation between these genera with the magnetic recovery of vanadium. Real time-qPCR confirmed the roles of functional genes of V(V) reduction (napA and nirK) and SO42- reduction (dsrA) in such biological processes. This study provides a novel route to sustainable V(V) remediation in aquifers, with synchronous recovery of vanadium resources without rebound.

The biochemical behavior and mechanism of uranium(Ⅵ) bioreduction induced by natural Bacillus thuringiensis

For a broader understanding of uranium migration affected by microorganisms in natural anaerobic environment, the bioreduction of uranium(Ⅵ) (U(Ⅵ)) was revealed in Bacillus thuringiensis, a dominant bacterium strain with potential of uranium-tolerant isolated from uranium contaminated soil. The reduction behavior was systematically investigated by the quantitative analysis of U(Ⅳ) in bacteria, and mechanism was inferred from the pathway of electron transmission. Under anaerobic conditions, appropriate biomass and sodium lactate as electron donor, reduction behavior of U(Ⅵ) induced by B. thuringiensis was restricted by the activity of lactate dehydrogenase, which was directly affected by the initial pH, temperature and initial U(Ⅵ) concentration of bioreduction system. Bioreduction of U(Ⅵ) was driven by the generation of nicotinamide adenine dinucleotide (NADH) from enzymatic reaction of sodium lactate with various dehydrogenase. The transmission of the electrons from bacteria to U(Ⅵ) was mainly supported by the intracellular NADH dehydrogenase-ubiquinone system, this process could maintain the biological activity of cells.

Deciphering Vanadium Speciation in Smelting Ash and Adaptive Responses of Soil Microorganisms

Abundant smelting ash is discharged during pyrometallurgical vanadium (V) production. However, its associated V speciation and resultant ecological impact have remained elusive. In this study, V speciation in smelting ash and its influence on the metabolism of soil microorganisms were investigated. Smelting ashes from V smelters contained abundant V (19.6-115.9 mg/g). V(V) was the dominant species for soluble V, while solid V primarily existed in bioavailable forms. Previously unrevealed V nanoparticles (V-NPs) were prevalently detected, with a peak concentration of 1.3 × 1013 particles/g, a minimal size of 136.0 ± 0.6 nm, and primary constituents comprising FeVO4, VO2, and V2O5. Incubation experiments implied that smelting ash reshaped the soil microbial community. Metagenomic binning, gene transcription, and component quantification revealed that Microbacterium sp. and Tabrizicola sp. secreted extracellular polymeric substances through epsB and yhxB gene regulation for V-NPs aggregation to alleviate toxicity under aerobic operations. The V K-edge X-ray absorption near-edge structure (XANES) spectra suggested that VO2 NPs were oxidized to V2O5 NPs. In the anaerobic case, Comamonas sp. and Achromobacter sp. reduced V(V) to V(IV) for detoxification regulated by the napA gene. This study provides a deep understanding of the V speciation in smelting ash and microbial responses, inspiring promising bioremediation strategies to reduce its negative environmental impacts.

Biostimulation effect of different amendments on Cr(VI) recovering microbial community

The present study used Cr(VI)-polluted microcosms amended with lactate or yeast extract, and nonamended microcosms as control, to investigate how a native bacterial community varied in response to the treatment and during the pollutant removal. Results suggested that providing electron donors resulted in a proliferation of a few bacterial species, with the consequent decrease in observed species richness and evenness, and was a driving force for the bacterial compositional shift. Lactate promoted, in the first instance, the enrichment of fermentative bacteria belonging to Chromobacteriaceae, including Paludibacterium, and Micrococcaceae as observed after 4 days. When the rate of Cr(VI) removal was maximum in microcosms amended with lactate, the most represented taxa were Pseudarcicella and Azospirillum. Using yeast extract as a carbon source and electron donor led instead to the significant enrichment of Shewanella, followed by Vogesella and Acinetobacter on the 4th day, corresponding to 90% of Cr(VI) removed from the system. After the complete Cr(VI) removal, achieved in 7 days in the presence of yeast extract, α-diversity was notably increased. The amendment-specific turnover of the enriched bacterial taxa resulted in a different kinetic of pollutant removal. In particular, yeast extract promoted the quickest Cr(VI) reduction, while lactate supported a slower, but also considerable, pollutant removal from water. Since it is reasonable to assume that a macroscopic effect, such as the observed Cr(VI) removal, involved the overrepresented taxa, deepening the knowledge of the native bacterial community and its changes were used to hypothesize the possible microbial pathways involved.

Elucidating Multiple Electron-Transfer Pathways for Metavanadate Bioreduction by Actinomycetic Streptomyces microflavus

While microbial reduction has gained widespread recognition for efficiently remediating environments polluted by toxic metavanadate [V(V)], the pool of identified V(V)-reducing strains remains rather limited, with the vast majority belonging to bacteria and fungi. This study is among the first to confirm the V(V) reduction capability of Streptomyces microflavus, a representative member of ubiquitous actinomycetes in environment. A V(V) removal efficiency of 91.0 ± 4.35% was achieved during 12 days of operation, with a maximum specific growth rate of 0.073 d-1. V(V) was bioreduced to insoluble V(IV) precipitates. V(V) reduction took place both intracellularly and extracellularly. Electron transfer was enhanced during V(V) bioreduction with increased electron transporters. The electron-transfer pathways were revealed through transcriptomic, proteomic, and metabolomic analyses. Electrons might flow either through the respiratory chain to reduce intracellular V(V) or to cytochrome c on the outer membrane for extracellular V(V) reduction. Soluble riboflavin and quinone also possibly mediated extracellular V(V) reduction. Glutathione might deliver electrons for intracellular V(V) reduction. Bioaugmentation of the aquifer sediment with S. microflavus accelerated V(V) reduction. The strain could successfully colonize the sediment and foster positive correlations with indigenous microorganisms. This study offers new microbial resources for V(V) bioremediation and improve the understanding of the involved molecular mechanisms.

Upcycling spent palladium-based catalysts into high value-added catalysts via electronic regulation of Escherichia coli to high-efficiently reduce hexavalent chromium

Upgrading and recycling Palladium (Pd) from spent catalysts may address Pd resource shortages and environmental problems. In this paper, Escherichia coli (E. coli) was used as an electron transfer intermediate to upcycle spent Pd-based catalysts into high-perform hexavalent chromium bio-catalysts. The results showed that Pd (0) nanoparticles (NPs) combined with the bacterial surface changed the electron transfer by enhancing the cell conductivity, thus promoting the removal rate of Pd(II). The recovery efficiency of Pd exceeded 98.6%. Notably, E. coli heightened the adsorption of H• and HCOO• via electron transfer of the Pd NPs electron-rich centre, resulting in a higher catalytic performance of the recycled spent catalysed the reduction of 20 ppm Cr(VI) under mild conditions within 18 min, in which maintained above 98% catalytic activity after recycling five times. This efficiency was found to be higher than that of the reported Pd-based catalysts. Hence, an electron transfer mechanism for E. coli recovery Pd-based catalyst under electron donor adjusting is proposed. These findings provide an important method for recovering Pd NPs from spent catalysts and are crucial to effectively reuse Pd resources.

Nitrogen-rich carbon composite fabricated from waste shrimp shells for highly efficient oxo-vanadate adsorption-coupled reduction

Protein, calcium carbonate, and chitin are abundant in shrimp shells. In this study, chemical treatment followed by hydrothermal carbonization was used to synthesize the nitrogen-rich hydrochar (HSHC) from shrimp shells. The untreated hydrochar exhibited a higher amount of calcium (25.37%) and less amount of nitrogen (2.68%) with alkaline pH (9.1). Interestingly chemical pre-treatment on shrimp shells boosted the nitrogen content to 6.81% and eliminated the calcium while controlling the pH to 6.4, which was beneficial for oxo-vanadate removal. The HSHC achieved vanadium(V) adsorption capacity of 21.20 mg/g at an optimal solution pH of 3.0, whereas the pristine hydrochar performed poorly (0.66 mg/g). The abundance of oxygen and nitrogen-based functional groups that developed through the chemical treatment resulted in improved adsorption coupled reduction performance of HSHC. This study proposed an inexpensive and environmentally friendly method for converting waste shrimp shells into value-added adsorbent.

Bioelectrochemical system accelerates reductive dechlorination through extracellular electron transfer networks

Bioelectrochemical system is considered as a promising approach for enhanced bio-dechlorination. However, the mechanism of extracellular electron transfer in the dechlorinating consortium is still a controversial issue. In this study, bioelectrochemical systems were established with cathode potential settings at -0.30 V (vs. SHE) for trichloroethylene reduction. The average dechlorination rate (102.0 μM Cl·d-1) of biocathode was 1.36 times higher than that of open circuit (74.7 μM Cl·d-1). Electrochemical characterization via cyclic voltammetry illustrated that electrostimulation promoted electrochemical activity for redox reactions. Moreover, bacterial community structure analyses indicated electrical stimulation facilitated the enrichment of electroactive and dechlorinating populations on cathode. Metagenomic and quantitative polymerase chain reaction (qPCR) analyses revealed that direct electron transfer (via electrically conductive pili, multi-heme c-type cytochromes) between Axonexus and Desulfovibrio/cathode and indirect electron transfer (via riboflavin) for Dehalococcoides enhanced dechlorination process in BES. Overall, this study verifies the effectiveness of electrostimulated bio-dechlorination and provides novel insights into the mechanisms of dechlorination process enhancement in bioelectrochemical systems through electron transfer networks.

Vanadium in the Environment: Biogeochemistry and Bioremediation

Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and (micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.

Effects of ferrous sulfate modification on the fate of phosphorous in sewage sludge biochar and its releasing mechanisms in heavy metal contaminated soils

Modifications of sludge biochar with metal-based materials can enhance its fertilizing efficiency and improve safety. To elucidate the effects of ferrous sulfate modification on the fate of phosphorus in sludge biochar and its effect on phosphorus fractionation in soil, we investigated the changes in fractionation and bioavailability of phosphorus in modified sludge biochar and studied the changes in soil characteristics, microbial diversity and response, bioavailability, plant uptake of phosphorus, and heavy metals in contaminated soils after treatment with ferrous sulfate modified sludge biochar. The results demonstrated that ferrous sulfate modifications were conducive to the formation of moderately labile phosphorus in sludge biochar, and the concentrations increased by a factor of 2.7 compared to control. The application of ferrous sulfate-modified sludge biochar to alkaline heavy metal-contaminated soils enhanced the bioavailable, labile, and moderately labile phosphorus contents by a factor of 2.9, 3.0, and 1.6, respectively, whereas it obviously reduced the leachability and bioavailability of heavy metals in soils, exhibited great potentials in the fertilization and remediation of actual heavy metal-contaminated soils in mining areas. The biochar-induced reduction in soil pH, enhancement of organic matter, surface oxygen-containing functional groups, the abundance of Gammaproteobacteria, and its phosphonate degradation activity were primarily responsible for the solubilization of phosphorus from modified biochar in heavy metal-contaminated soils.

Cross-sectional and longitudinal relationships between ozone exposure and glucose homeostasis: Exploring the role of systemic inflammation and oxidative stress in a general Chinese urban population

The adverse health effects of ozone pollution have been a globally concerned public health issue. Herein we aim to investigate the association between ozone exposure and glucose homeostasis, and to explore the potential role of systemic inflammation and oxidative stress in this association. A total of 6578 observations from the Wuhan-Zhuhai cohort (baseline and two follow-ups) were included in this study. Fasting plasma glucose (FPG) and insulin (FPI), plasma C-reactive protein (CRP, biomarker for systemic inflammation), urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG, biomarker for oxidative DNA damage), and urinary 8-isoprostane (biomarker for lipid peroxidation) were repeatedly measured. After adjusting for potential confounders, ozone exposure was positively associated with FPG, FPI, and homeostasis model assessment of insulin resistance (HOMA-IR), and negatively associated with HOMA of beta cell function (HOMA-β) in cross-sectional analyses. Each 10 ppb increase in cumulative 7-days moving average ozone was associated with a 13.19%, 8.31%, and 12.77% increase in FPG, FPI, and HOMA-IR, respectively, whereas a 6.63% decrease in HOMA-β (all P < 0.05). BMI modified the associations of 7-days ozone exposure with FPI and HOMA-IR, and the effects were stronger in subgroup whose BMI ≥24 kg/m². Consistently high exposure to annual average ozone was associated with increased FPG and FPI in longitudinal analyses. Furthermore, ozone exposure was positively related to CRP, 8-OHdG, and 8-isoprostane in dose-response manner. Increased CRP, 8-OHdG, and 8-isoprostane could dose-dependently aggravate glucose homeostasis indices elevations related to ozone exposure. Increased CRP and 8-isoprostane mediated 2.11-14.96% of ozone-associated glucose homeostasis indices increment. Our findings suggested that ozone exposure could cause glucose homeostasis damage and obese people were more susceptible. Systemic inflammation and oxidative stress might be potential pathways in glucose homeostasis damage induced by ozone exposure.

Transcriptomic and metabolomic perspectives for the growth of alfalfa (Medicago sativa L.) seedlings with the effect of vanadium exposure

Hitherto, the effect of vanadium on higher plant growth remains an open topic. Therefore, nontargeted metabolomic and RNA-Seq profiling were implemented to unravel the possible alteration in alfalfa seedlings subjected to 0.1 mg L^-1 (B group) and 0.5 mg L^-1 (C group) pentavalent vanadium [(V(V)] versus control (A group) in this study. Results revealed that vanadium exposure significantly altered some pivotal transcripts and metabolites. The number of differentially expressed genes (DEGs) markedly up- and down-regulated was 21 and 23 in B_vs_A, 27 and 33 in C_vs_A, and 24 and 43 in C_vs_B, respectively. The number for significantly up- and down-regulated differential metabolites was 17 and 15 in B_vs_A, 43 and 20 in C_vs_A, and 24 and 16 in C_vs_B, respectively. Metabolomics and transcriptomics co-analysis characterized three significantly enriched metabolic pathways in C_vs_A comparing group, viz., α-linolenic acid metabolism, flavonoid biosynthesis, and phenylpropanoid biosynthesis, from which some differentially expressed genes and differential metabolites participated. The metabolite of traumatic acid in α-linolenic acid metabolism and apigenin in flavonoid biosynthesis were markedly upregulated, while phenylalanine in phenylpropanoid biosynthesis was remarkably downregulated. The genes of allene oxide cyclase (AOC) and acetyl-CoA acyltransferase (fadA) in α-linolenic acid metabolism, and chalcone synthase (CHS), flavonoid 3'-monooxygenase (CYP75B1), and flavonol synthase (FLS) in flavonoid biosynthesis, and caffeoyl-CoA O-methyltransferase (CCoAOMT) in phenylpropanoid biosynthesis were significantly downregulated. While shikimate O-hydroxycinnamoyltransferase (HCT) in flavanoid and phenylpropanoid biosynthesis were conspicuously upregulated. Briefly, vanadium exposure induces a readjustment yielding in metabolite and the correlative synthetic precursors (transcripts/unigenes) in some branched metabolic pathways. This study provides a practical and in-depth perspective from transcriptomics and metabolomics in investigating the effects conferred by vanadium on plant growth and development.

Functional characterization of a DNA-damage repair/tolerance 100 (DRT100) gene in Sedum alfredii Hance for genome stability maintenance and Cd hypertolerance

Cd contamination is a world-wild concern for its toxicity and accumulation in food chain. Sedum alfredii Hance (Crassulaceae) is a zinc (Zn) and cadmium (Cd) hyperaccumulator native to China and widely applied for the phytoremediation at Zn or Cd contaminated sites. Although many studies report the uptake, translocation and storage of Cd in S. alfredii Hance, limited information is known about the genes and underlying mechanisms of genome stability maintenance under Cd stress. In this study, a gene resembling DNA-damage repair/toleration 100 (DRT100) was Cd inducible and designated as SaDRT100. Heterologous expression of SaDRT100 gene in yeasts and Arabidopsis thaliana enhanced Cd tolerance capability. Under Cd stress, transgenic Arabidopsis with SaDRT100 gene exhibited lower levels of reactive oxygen species (ROS), fewer Cd uptake in roots and less Cd-induced DNA damage. Evidenced by the subcellular location in cellular nucleus and expression in aerial parts, we suggested the involvement of SaDRT100 in combating Cd-induced DNA damage. Our findings firstly uncovered the roles of SaDRT100 gene in Cd hypertolerance and genome stability maintenance in S. alfredii Hance. The potential functions of DNA protection make SaDRT100 gene a candidate in genetic engineering for phytoremediation at multi-component contaminated sites.

Bioleaching performance of vanadium-bearing smelting ash by Acidithiobacillus ferrooxidans for vanadium recovery

The bioleaching process is widely used in the treatment of ores or solid wastes, but little is known about its application in the treatment of vanadium-bearing smelting ash. This study investigated bioleaching of smelting ash with Acidithiobacillus ferrooxidans. The vanadium-bearing smelting ash was first treated with 0.1 M acetate buffer and then leached in the culture of Acidithiobacillus ferrooxidans. Comparison between one-step and two-step leaching process indicated that microbial metabolites could contribute to the bioleaching. The Acidithiobacillus ferrooxidans demonstrated a high vanadium leaching potential, solubilizing 41.9% of vanadium from the smelting ash. The optimal leaching condition was determined, which was 1% pulp density, 10% inoculum volume, an initial pH of 1.8, and 3 Fe²⁺g/L. The compositional analysis showed that the fraction of reducible, oxidizable, and acid-soluble was transferred into the leaching liquor. Therefore, as the alternative to the chemical/physical process, an efficient bioleaching process was proposed to enhance the recovery of vanadium from the vanadium-bearing smelting ash.

Sequentially modified carbon felt for enhanced p-nitrophenol biodegradation through direct interspecific electron transfer

The widely applied aromatic nitration in modern industry leads to toxic p-nitrophenol (PNP) in environment. Exploring its efficient degradation routes is of great interests. In this study, a novel four-step sequential modification procedure was developed to increase the specific surface area, functional group, hydrophilicity, and conductivity of carbon felt (CF). The implementation of the modified CF promoted reductive PNP biodegradation, attaining 95.2 ± 0.8% of removal efficiency with less accumulation of highly toxic organic intermediates (e.g., p-aminophenol), compared to carrier-free and CF-packed biosystems. The constructed anaerobic-aerobic process with modified CF in 219-d continuous operation achieved further removal of carbon and nitrogen containing intermediates and partial mineralization of PNP. The modified CF promoted the secretion of extracellular polymeric substances (EPS) and cytochrome c (Cyt c), which were essential components to facilitate direct interspecies electron transfer (DIET). Synergistic relationship was deduced that glucose was converted into volatile fatty acids by fermenters (e.g., Longilinea and Syntrophobacter), which donated electrons to the PNP degraders (e.g., Bacteroidetes_vadinHA17) through DIET channels (CF, Cyt c, EPS) to complete PNP removal. This study proposes a novel strategy using engineered conductive material to enhance the DIET process for efficient and sustainable PNP bioremediation.

Fe(III) enhances Cr(VI) bioreduction in a MFC-granular sludge coupling system: Experimental evidence and metagenomics analysis

The influence of Fe(III) on the bioreduction efficiency of Cr(VI) in a microbial fuel cell (MFC)-granular sludge coupling system using dissolved methane as an electron donor and carbon source was explored, and the mechanism of Fe(III) mediating enhancement in the bioreduction process of Cr(VI) in the coupling system was also investigated. Results showed that the presence of Fe(III) enhanced the ability of the coupling system to reduce Cr(VI). The average removal efficiencies of Cr(VI) in the anaerobic zone in response to 0, 5, and 20 mg/L of Fe(III) were 16.53±2.12%, 24.17±2.10%, and 46.33±4.41%, respectively. Fe(III) improved the reducing ability and output power of the system. In addition, Fe(III) enhanced the electron transport systems activity of the sludge, the polysaccharide and protein content in the anaerobic sludge. Meanwhile, X-ray photoelectron spectrometer (XPS) spectra demonstrated that Cr(VI) was reduced to Cr(III), while Fe2p participated in reducing Cr(VI) in the form of Fe(III) and Fe(II). Proteobacteria, Chloroflexi, and Bacteroidetes were the dominant phylum in the Fe(III)-enhanced MFC-granular sludge coupling system, accounting for 49.7%-81.83% of the microbial community. The relative abundance of Syntrophobacter and Geobacter increased after adding Fe(III), indicating that Fe(III) contributed to the microbial mediated anaerobic oxidation of methane (AOM) and bioreduction of Cr(VI). The genes mcr, hdr, and mtr were highly expressed in the coupling system after the Fe(III) concentration increased. Meanwhile, the relative abundances of coo and aacs genes were up-regulated by 0.014% and 0.075%, respectively. Overall, these findings deepen understanding of the mechanism of the Cr(VI) bioreduction in the MFC-granular sludge coupling system driven by methane under the influence of Fe(III).

Enhanced selective separation of vanadium(V) and chromium(VI) using the CeO2 nanorod containing oxygen vacancies

Adsorption of vanadium from wastewater defends the environment from toxic ions and contributes to recover the valuable metal. However, it is still challenging for the separation of vanadium (V⁵⁺) and chromium (Cr⁶⁺) because of their similar properties. Herein, a kind of CeO₂ nanorod containing oxygen vacancies is facilely synthesized which displays ultra-high selectivity of V⁵⁺ against various competitive ions (i.e., Fe, Mn, Cr, Ni, Cu, Zn, Ga, Cd, Ba, Pb, Mg, Be, and Co). Moreover, a large separation factor (SF_V/Cr) of 114,169.14 for the selectivity of V⁵⁺ is achieved at the Cr⁶⁺/V⁵⁺ ratio of 80 with the trace amount of V⁵⁺ (~ 1 mg/L). The results show that the process of V⁵⁺ uptake is the monolayer homogeneous adsorption and is controlled by external and intraparticle diffusions. In addition, it also shows that V⁵⁺ is reduced to V³⁺ and V⁴⁺ and then formation of V-O complexation. This work offers a novel CeO₂ nanorod material for efficient separation of V⁵⁺ and Cr⁶⁺ and also clarifies the mechanism of the V⁵⁺ adsorption on the CeO₂ surface.

Dynamics of vanadium and response of inherent bacterial communities in vanadium-titanium magnetite tailings to beneficiation agents, temperature, and illumination

Vanadium-titanium (V-Ti) magnetite tailings contain toxic metals that could potentially pollute the surrounding environment. However, the impact of beneficiation agents, an integral part of mining activities, on the dynamics of V and the microbial community composition in tailings remains unclear. To fill this knowledge gap, we compared the physicochemical properties and microbial community structure of V-Ti magnetite tailings under different environmental conditions, including illumination, temperature, and residual beneficiation agents (salicylhydroxamic acid, sodium isobutyl xanthate, and benzyl arsonic acid) during a 28-day reaction. The results revealed that beneficiation agents exacerbated the acidification of the tailings and the release of V, among which benzyl arsonic acid had the greatest impact. The concentration of soluble V in the leachate of tailings with benzyl arsonic acid was 6.4 times higher than that with deionized water. Moreover, illumination, high temperatures, and beneficiation agents contributed to the reduction of V in V-containing tailings. High-throughput sequencing revealed that Thiobacillus and Limnohabitans adapted to the tailings environment. Proteobacteria was the most diverse phylum, and the relative abundance was 85.0%-99.1%. Desulfovibrio, Thiobacillus, and Limnohabitans survived in the V-Ti magnetite tailings with residual beneficiation agents. These microorganisms could contribute to the development of bioremediation technologies. The main factors affecting the diversity and composition of bacteria in the tailings were Fe, Mn, V, SO₄^2-, total nitrogen, and pH of the tailings. Illumination inhibited microbial community abundance, while the high temperature (39.5 °C) stimulated microbial community abundance. Overall, this study strengthens the understanding of the geochemical cycling of V in tailings influenced by residual beneficiation agents and the application of inherent microbial techniques in the remediation of tailing-affected environments.

Thermally enhanced biodegradation of benzo[a]pyrene and benzene co-contaminated soil: Bioavailability and generation of ROS

In this study, a set of comprehensive experiments were conducted to explore the effects of temperature on the biodegradation, bioavailability, and generation of reactive oxygen species (ROS) by thermally enhanced biodegradation (TEB) under benzene and BaP co-contaminated conditions. The biodegradation rates of benzene increased from 57.4% to 88.7% and 84.9%, and the biodegradation efficiency of BaP was enhanced from 15.8% to 34.6% and 28.6%, when the temperature was raised from the ambient temperature of 15 °C to 45 °C and 30 °C, respectively. In addition, the bioavailability analysis results demonstrated that the water- and butanol-extractable BaP increased with elevated temperatures. High enzymatic activities and PAH-RHD_α gene in gram-positive bacteria favored the long-term elevated temperatures (30 and 45 °C) compared to gram-negative bacteria. Moreover, ROS species (O₂^•- and •OH) generation was detected which were scavenged by the increased superoxide dismutase and catalase activities at elevated temperatures. Soil properties (pH, TOC, moisture, total iron, Fe³⁺, and Fe²⁺) were affected by the temperature treatments, revealing that metal-organic-associated reactions occurred during the TEB of benzene-BaP co-contamination. The results concluded that biodegradation of benzene-BaP co-contamination was greatly improved at 45 °C and that microbial activities enhanced the biodegradation under TEB via the increased bioavailability and generation and degradation of ROS.

Electron transfer routes in nitrate-pentavalent vanadium co-contaminated system of oligotrophic microbiology niche

Microbial techniques have been extensively used for the remediation of nitrate and V(V) co-contaminations, but the mechanisms of electron and substances transport and metabolism of co-contaminations under oligotrophic niche have been largely overlooked. This study quantified the electron transfer and consumption, substance transfer, and metabolic pathways in the nitrate and V(V) co-contamination system under oligotrophic condition to explore the underlying mechanisms by characterizing the products and elucidating conventional cognitive pathways. This study compared the composition of the precipitates under the conditions of sufficient and insufficient carbon sources using energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and discovered the re-oxidation process of the already reduced V(IV). Electronic evidence for the re-oxidation process of V(IV) was also provided by electron transfer and quantitative analysis. Besides, this study found that the electron contribution ratio of NO₃^--N → NO₂^--N and V(V) → V(IV) reduction was 40.2:1. In addition, based on the functional prediction of PICRUSt 2, it was found that the utilization of intracellular reserve carbon source and enzymes in the transport chain were enhanced in oligotrophic microbiology niche. These results provide new insights into the stability of co-contamination reduction in oligotrophic microbiology niche and demonstrate a new mobilization pathway for V(V) in oligotrophic systems.

A sustainable vanadium bioremediation strategy from aqueous media by two potential green microalgae

Globally, environmental concerns are rapidly growing due to increasing pollution levels. Vanadium is a hazardous heavy metal that poses health issues with an exposure concentration of about 2 ppm. It is regularly discharged by some industries and poses an environmental challenge. There are no sustainable green treatment methods for discharged effluents to mitigate vanadium threats to humans and the environment. In this study, the goal was to develop a green, sustainable method for removing vanadium and to utilize the produced biomass for biofuels, thus offsetting the treatment cost. Microalgae Chlorella sorokiniana SU1 and Picochlorum oklahomensis were employed for vanadium (III) treatment. The maximum removal was 25.5 mg L^-1 with biomass and lipid yields of 3.0 g L^-1 and 884.4 mg L^-1 respectively after 14 days of treatment. The vanadium removal capacity by microalgae was further enhanced up to 2-2.7 folds while optimizing the key parameters, pH, and temperature before removing biomass from the liquid phase. FTIR is used to analyse the reactive groups in algal cell walls to confirm vanadium adsorption and to understand the dominant and quantitative interactions. Zeta potential analysis helps to find out the most suitable pH range to facilitate the ionic bonding of biomass and thus maximum vanadium adsorption. This study addresses regulating external factors for enhancing the removal performance during microalgal biomass harvesting, which significantly enhances the removal of vanadium (III) from the aqueous phase. This strategy aims to improve the removal efficiency of microalgal treatment at an industrial scale for the bioremediation of vanadium and other inorganic pollutants.

Independent and synergistic bio-reductions of uranium (VI) driven by zerovalent iron in aquifer

Zerovalent iron [Fe(0)] can donate electron for bioprocess, but microbial uranium (VI) [U(VI)] reduction driven by Fe(0) is still poorly understood. In this study, Fe(0) supported U(VI) bio-reduction was steadily achieved in the 160-d continuous-flow biological column. The maximum removal efficiency and capacity of U(VI) were 100% and 46.4 ± 0.52 g/(m³·d) respectively, and the longevity of Fe(0) increased by 3.09 times. U(VI) was reduced to solid UO₂, while Fe(0) was finally oxidized to Fe(III). Autotrophic Thiobacillus achieved U(VI) reduction coupled to Fe(0) oxidation, verified by pure culture. H₂ produced from Fe(0) corrosion was consumed by autotrophic Clostridium for U(VI) reduction. The detected residual organic intermediates were biosynthesized with energy released from Fe(0) oxidation and utilized by heterotrophic Desulfomicrobium, Bacillus and Pseudomonas to reduce U(VI). Metagenomic analysis found the upregulated genes for U(VI) reduction (e.g., dsrA and dsrB) and Fe(II) oxidation (e.g., CYC1 and mtrA). These functional genes were also transcriptionally expressed. Cytochrome c and glutathione responsible for electron transfer also contributed to U(VI) reduction. This study reveals the independent and synergistic pathways for Fe(0)-dependent U(VI) bio-reduction, providing promising remediation strategy for U(VI)-polluted aquifers.

Study on the coordination conduct and kinetic insights within the oxo-vanadate and organic reductive nitrogen and sulfur functionalities during the reduction coupled adsorption processes: Implications in practical applications

Vanadium(V) is arising wastewater contaminant recently. Although bio-reduction of vanadium(V) is effective, the knowledge of electron transfer pathways and coordination nature by cellular organic functionalities is seriously lacking. Herein, the coordination conduct and kinetic modes for the reduction of V(V) by organic nitrogen and sulfur functionalities in working pHs are comprehensively investigated for the first time. The kinetics follow 3 steps; (1) diffusion of V(V) species, (2) reduction of V(V) to V(IV), and (3) adsorption of existing V species. The diffusion of V(V) is controlled by the protonated =NH₂⁺, -SH₂⁺, -CSH⁺ functional groups and oxo-vanadate speciation. The reduction of V(V) to V(IV) was efficient by -SH than =NH, -NH- , because of the higher oxidation potential of sulfur and which acted as the sole electron donor in the process. The coordination of V(V)/V(IV) species interacted with oxygen, nitrogen and sulfur atoms via parallel orientation and leads to multi-docking or single-ionic interactions, revealing the previously unrecognized track. Hence, the system tested in four types of wastewaters with different pHs and resulted the comprehensive practical applicability of the system. This study proposes a novel tactic to design an efficient V(V) wastewater treatment system by considering its water parameters.

Insights into the shift of microbial community related to nitrogen cycle, especially N2O in vanadium-polluted soil

Soil is a vital contributor to the production of nitrous oxide (N₂O), a potent greenhouse gas, through the nitrogen cycle, which can be influenced by accumulated vanadium (V) in soil but it is less pronounced. This work investigated the response of soil N₂O fluxes along with major nitrogen cycle products (ammonium, nitrate, and nitrite) to different vanadium contents (0, 200, 500, 800, and 1100 mg V/kg), and the underlying microbial mechanisms. N₂O fluxes was significantly influenced at high V content (1100 mg V/kg) due to its corresponding high water-soluble V content. Microbial composition and their correlations with nitrogen cycle products showed that microbes in dominant phyla (Actinobacteriota and Proteobacteria) and genus (Nocardioides, Lysobacter, Sphingomonas, and Marmoricola) might be the important contributor to N₂O fluxes regardless of the V content. Moreover, high V contents (800, and 1100 mg V/kg) could enrich microbes involved in nitrogen cycle, but weaken their correlations with nitrogen-related products, such as in genus Bacillus, and change microbial correlation with N₂O from associated with nitrate and nitrite to ammonium. Meanwhile, functional gene predication results showed that denitrifying genes nirKS and nosZ were negatively and positively correlated with V contents, respectively. These all further suggested that the shift of possible N₂O metabolic pathways induced mainly by water-soluble V might be the underlying reason for N₂O fluxes. These findings promote an understanding of the potential effect of metal pollution on N₂O fluxes in soil.

Arsenic release from microbial reduction of scorodite in the presence of electron shuttle in flooded soil

Scorodite (FeAsO₄·H₂O) is a common arsenic-bearing (As-bearing) iron mineral in near-surface environments that could immobilize or store As in a bound state. In flooded soils, microbe induced Fe(III) or As(V) reduction can increase the mobility and bioavailability of As. Additionally, humic substances can act as electron shuttles to promote this process. The dynamics of As release and diversity of putative As(V)-reducing bacteria during scorodite reduction have yet to be investigated in detail in flooded soils. Here, the microbial reductive dissolution of scorodite was conducted in an flooded soil in the presence of anthraquinone-2,6-disulfonate (AQDS). Anaeromyxobacter, Dechloromonas, Geothrix, Geobacter, Ideonella, and Zoogloea were found to be the dominant indigenous bacteria during Fe(III) and As(V) reduction. AQDS increased the relative abundance of dominant species, but did not change the diversity and microbial community of the systems with scorodite. Among these bacteria, Geobacter exhibited the greatest increase and was the dominant Fe(III)- and As(V)-reducing bacteria during the incubation with AQDS and scorodite. AQDS promoted both Fe(III) and As(V) reduction, and over 80% of released As(V) was microbially transformed to As(III). The increases in the abundance of arrA gene and putative arrA sequences of Geobacter were higher with AQDS than without AQDS. As a result, the addition of AQDS promoted microbial Fe(III) and As(V) release and reduction from As-bearing iron minerals into the environment. These results contribute to exploration of the transformation of As from As-bearing iron minerals under anaerobic conditions, thus providing insights into the bioremediation of As-contaminated soil.

Biological Consequences of Vanadium Effects on Formation of Reactive Oxygen Species and Lipid Peroxidation

Lipid peroxidation (LPO), a process that affects human health, can be induced by exposure to vanadium salts and compounds. LPO is often exacerbated by oxidation stress, with some forms of vanadium providing protective effects. The LPO reaction involves the oxidation of the alkene bonds, primarily in polyunsaturated fatty acids, in a chain reaction to form radical and reactive oxygen species (ROS). LPO reactions typically affect cellular membranes through direct effects on membrane structure and function as well as impacting other cellular functions due to increases in ROS. Although LPO effects on mitochondrial function have been studied in detail, other cellular components and organelles are affected. Because vanadium salts and complexes can induce ROS formation both directly and indirectly, the study of LPO arising from increased ROS should include investigations of both processes. This is made more challenging by the range of vanadium species that exist under physiological conditions and the diverse effects of these species. Thus, complex vanadium chemistry requires speciation studies of vanadium to evaluate the direct and indirect effects of the various species that are present during vanadium exposure. Undoubtedly, speciation is important in assessing how vanadium exerts effects in biological systems and is likely the underlying cause for some of the beneficial effects reported in cancerous, diabetic, neurodegenerative conditions and other diseased tissues impacted by LPO processes. Speciation of vanadium, together with investigations of ROS and LPO, should be considered in future biological studies evaluating vanadium effects on the formation of ROS and on LPO in cells, tissues, and organisms as discussed in this review.

Degradation of alkane hydrocarbons by Priestia megaterium ZS16 and sediments consortia with special reference to toxicity and oxidative stress induced by the sediments in the vicinity of an oil refinery

Petroleum hydrocarbon is a critical ecological issue with impact on ecosystems through bioaccumulation. It poses significant risks to human health. Due to the extent of alkane hydrocarbon pollution in some environments, biosurfactants are considered as a new multifunctional technology for the efficient removal of petroleum-based contaminants. To this end, Yamuna river sediments were collected at different sites in the vicinity of Mathura oil refinery, UP (India). They were analysed by atomic absorption spectrophotometry and gas chromatography-mass spectrometry (GC-MS) for heavy metals and organic pollutants. Heptadecane, nonadecane, oleic acid ester and phthalic acid were detected. In total 107 bacteria were isolated from the sediments and screened for biosurfactant production. The most efficient biosurfactant producing strain was tested for its capability to degrade hexadecane efficiently at different time intervals (0 h, 7 d, 14 d and 21 d). FT-IR analysis defined the biosurfactant as lipopeptide. 16S rRNA gene sequencing identified the bacterium as Priestia megaterium. The strain lacks resistance to common antibiotics thus making it an important candidate for remediation. The microbial consortia present in the sediments were also investigated for their capability to degrade C₁₆, C₁₇ and C₁₈ alkane hydrocarbons. By using gas chromatography-mass spectrophotometry the metabolites were identified as 1-docosanol, dodecanoic acid, 7-hexadecenal, (Z)-, hexadecanoic acid, docosanoic acid, 1-hexacosanal, 9-octadecenoic acid, 3-octanone, Z,Z-6,28-heptatriactontadien-2-one, heptacosyl pentafluoropropionate, 1,30-triacontanediol and decyl octadecyl ester. Oxidative stress in Vigna radiata L. roots was observed by using Confocal Laser Scanning Microscopy. A strong reduction in seed germination and radicle and plumule length was observed when Vigna radiata L. was treated with different concentrations of sediment extracts, possibly due to the toxic effects of the pollutants in the river sediments. Thus, this study is significant since it considers the toxicological effects of hydrocarbons and to degrade them in an environmentally friendly manner.

The parallel electron transfer pathways of biofilm and self-secreted electron shuttles in gram-positive strain Rhodococcus pyridinivorans HR-1 inoculated microbial fuel cell

Microbial fuel cell (MFC) exhibits huge potentials in disposing wastewater and extra energy consumption. Exploring useful microorganisms for MFC is the crucial section. Herein, the electrochemical mechanism of extracellular anaerobic respiration in MFC inoculated with gram-positive Rhodococcus pyridinivorans HR-1, was first revealed. The MFC exhibited rapid recovery of currents on anode, and could recover to maximum output within one hour, with redox peaks near -0.38 and -0.18 V through electron transfer between the biofilm and anode. When the biofilm-based pathway was blocked by wrapping the anode with Millipore filter membrane, HR-1 inoculated MFC could still generate electricity within a longer recovery period (∼35 h) during anolyte exchange. This was proposed as a self-secreted electron shuttle pathway for electron transfer in R. pyridinivorans HR-1. Cyclic voltammetry analysis revealed that the biofilm-based and self-secreted electron shuttle-based pathways co-existed in R. pyridinivorans HR-1 inoculated MFC, which could play synergistic roles in electricity generation.

Enhanced biological S0 accumulation by using signal molecules during simultaneous desulfurization and denitrification

A high rate of elemental sulfur (S⁰) accumulation from sulfide-containing wastewater has great significance in terms of resource recovery and pollution control. This experimental study used Thiobacillus denitrificans and denitrifying bacteria incorporated with signal molecules (C6 and OHHL) for simultaneous sulfide (S^2-) and nitrate (NO₃^-) removal in synthetic wastewater. Also, the effects on S⁰ accumulation due to changes in organic matter composition and bacteria proportion through signal molecules were analyzed. The 99.0% of S^2- removal and 99.3% of NO₃^- was achieved with 66% of S⁰ accumulation under the active S^2- removal group. The S⁰ accumulation, S^2- and NO₃^- removal mainly occurred in 0-48 h. The S⁰ accumulation in the active S^2- removal group was 2.0-6.3 times higher than the inactive S^2- removal groups. In addition, S⁰/SO₄^2- ratio exhibited that S⁰ conversion almost linearly increased with reaction time under the active S^2- removal group. The proportion of Thiobacillus denitrificans and H⁺ consumption showed a positive correlation with S⁰ accumulation. However, a very high or low ratio of H⁺/S⁰ is not suitable for S⁰ accumulation. The signal molecules greatly increased the concentration of protein-I and protein-II, which resulted in the high proportion of Thiobacillus denitrificans. Therefore, high S⁰ accumulation was achieved as Thiobacillus denitrificans regulated the H⁺ consumption and electron transfer rate and provided suppressed oxygen environment. This technology is cost-effective and commercially applicable for recovering S⁰ from wastewater.