Cr(VI) Reduction and Fe(II) Regeneration by Penicillium oxalicum SL2-Enhanced Nanoscale Zero-Valent Iron

Insights into biostimulation-enhanced microbial detoxification of chromium ore processing residue-contaminated soil: The critical role of Cr(VI) key host-phase transformation and soil microbiota shifts

The continuous and slow release of Cr(VI) from chromium ore processing residue contaminated soil (COPR-soil) poses a substantial threat to soil and groundwater. Despite microbial reduction is considered as an effective approach for the remediation of Cr(VI)-contaminated soil, the efficiency and rate of Cr(VI) reduction in COPR-soil, especially Cr(VI) embedded in minerals (e.g., vaterite, Ca/Al-Cr layered double hydroxide (Ca/Al-Cr LDH)) remain low. Here, a biostimulation-enhanced microbial detoxification strategy was developed, utilizing the strong electron transfer properties of FeSx. The removal efficiency of Cr(VI) from COPR-soil reached 99.9 %, with a 9-fold increase in the reduction rate of dissolved Cr(VI) compared to microbial remediation. FeSx semiconductor nanoparticles adhered tightly to the surface of the electroactive bacterium Pannonibacter phragmitetus BB (BB), facilitating mineral-microbial interactions that increased protein concentration by 35.8 % and Cr(VI) tolerance by 23.0 %. Biostimulation with FeSx significantly enhanced the biochemical dissolution capacity and electron shuttle potential of BB, accelerating the transformation of Cr(VI) host-phases. Vaterite was completely converted to calcite with a 22 % increase in transformation degree, while the interlayer nanoconfined Ca-Cr coordination in Ca/Al-Cr LDH shifted to a more accessible outer nonconfined structure. This transformation reduced the Cr(VI) binding capacity by 68.6 % and 79.4 %, respectively, effectively releasing Cr(VI) from mineral. Soluble Fe(III) emerged as a critical electron shuttle, enabling indirect electron transfer from BB to Cr(VI) via the Fe(III)/Fe(II) redox cycle. Additionally, biostimulation enhanced soil fertility and stability, fostering microbial consortia with improved resistance to environmental stresses through Cr(VI) efflux and intracellular translocation of Fe-Fe carrier complexes. This study provides a promising strategy to promote effective microbial remediation of COPR-soil.

Zeolitic imidazolate framework- cellulose loading GR(II)/Cu for efficient Cr(VI) removal over a wide pH range from water: Combined insights of capture performance and potential mechanism analysis

The development of efficient, stable, and user-friendly adsorbents for the removal of Cr(VI) from wastewater has become a hot issue for researchers. The present study focused on the synthesis of a composite material, namely zeolitic imidazolate framework (ZIF8)- cellulose loading GR(II)/Cu (MCH-ZIF8@GR(II)/Cu), aiming to leverage the advantages of each component for enhancing the rapid decontamination and removal efficiency of Cr(VI) from wastewater. The Cr(VI) removal efficiency of MCH-ZIF8@GR(II)/Cu composite reached nearly 100 % within the pH range of 3 to 4, remained above 90 % within the pH range of 5 to 6, and still maintained a significant removal rate of approximately 80 % even at a pH level of 7. Even in the presence of Ca2+, Mg2+, and CO32-, the removal efficiency remained approximately 90 %, exhibiting a high anti-interference ability. MCH-ZIF8@GR(II)/Cu composite exhibited outstanding cycling performance, with a Cr(VI) removal efficiency of 87.8 % even after undergoing five cycles. The main mechanism of Cr(VI) removal by MCH-ZIF8@GR(II)/Cu is primarily attributed to anion exchange, as supported by both experimental characterizations and DFT calculations. The present study demonstrates the superiority of anion exchange in the removal of Cr(VI) and offers a novel perspective for effectively treating wastewater contaminated with Cr(VI).

Iron(II/III) Alters the Relative Roles of the Microbial Byproduct and Humic Acid during Chromium(VI) Reduction and Fixation by Soil-Dissolved Organic Matter

Though reduction of hexavalent chromium (Cr(VI)) to Cr(III) by dissolved organic matter (DOM) is critical for the remediation of polluted soils, the effects of DOM chemodiversity and underlying mechanisms are not fully elucidated yet. Here, Cr(VI) reduction and immobilization mediated by microbial byproduct (MBP)- and humic acid (HA)-like components in (hot) water-soluble organic matter (WSOM), (H)WSOM, from four soil samples in tropical and subtropical regions of China were investigated. It demonstrates that Cr(VI) reduction capacity decreases in the order WSOM > HWSOM and MBP-enriched DOM > HA-enriched DOM due to the higher contents of low molecular weight saturated compounds and CHO molecules in the former. The presence of Fe(II/III) selectively coprecipitates with high molecular weight components (e.g., tannins, lignin, and CHON-rich compounds) to form ferrihydrite and greatly inhibits Cr(VI) transformation and fixation in MBP-enriched DOM but enhances that in HA-enriched DOM. This is probably owing to the combined effects of (1) the increase of DOM electron-donating capacity and Fe(II) generation during the reactions of HA with Fe(II) and Fe(III), respectively; (2) the enrichment of phenolic and carboxyl groups, aromatic compounds, and carbon defects on ferrihydrite surfaces; and (3) the acceleration of HA decomposition and MBP mineralization by hydroxyl radicals. These findings enhance our understanding of the chemodiversity of soil DOM, the complex interactions between Cr(VI), DOM, and Fe(II/III), and can help design remediation strategies for contaminated environments.

Identification of key chromium resistance genes in Cellulomonas using transcriptomics

Cellulomonas fimi Clb-11 can reduce high toxic Cr(VI) to less toxic Cr(III), and transcriptomics was used to reveal the key Cr(VI) uptake and reduction genes of C. fimi Clb-11 in this study. The results showed that under 0.5 mM Cr(VI) stress, 654 genes were upregulated. Among the upregulated genes, phosphate transport protein encoding genes phoU and TC.PIT, and molybdate transport protein encoding genes modA, modB, and modC were involved in the cell uptake of Cr(VI). Cytochrome c subunits encoding genes qcrA and qcrC were involved in the intracellular reduction of Cr(VI), and cytochrome c oxidase subunits encoding genes coxB and coxC were involved in extracellular electron secretion. Additionally, several unreported genes were found to be upregulated in C. fimi Clb-11 under Cr(VI) stress. The upregulated manganese transport protein encoding gene mntH may also assist Cr(VI) uptake in C. fimi Clb-11. Proton pump subunit encoding genes atpA, atpB, atpE, atpF, and atpH, as well as sodium-hydrogen antiporter subunit encoding genes mnhA and mnhC were upregulated, it may be involved in the extracellular proton secretion to reduce Cr(VI). Iron complex transport system substrate-binding protein encoding gene ABC.FEV.S, vacuolar iron transporter encoding gene VIT, FMN reductase gene encoding gene ssuE, and quinone oxidoreductase encoding genes qor and qorB were upregulated to reduce Cr(VI) in the intracellular. Our study showed theoretical importance by revealing the Cr(VI) reduction mechanism using chrome-resistant microorganisms.

Nano-micro materials regulated biocatalytic metabolism for efficient environmental remediation: Fine engineering the mass and electron transfer in multicellular environments

The escalating energy and environmental crises have spurred significant research interest into developing efficient biological remediation technologies for sustainable contaminant and resource conversion. Integrating engineered nano-micro materials (NMMs) with these biocatalytic processes offers a promising approach to improve the microbial performance for environmental remediation. Core to such material-enhanced hybrid biocatalysis systems (MHBSs) is the rational regulation of metabolic processes with the assistance of NMMs, where a fine engineered mass and electron transfer is beneficial for the improved biocatalytic activity. However, the specific mechanisms of those NMMs-enhanced microbial metabolisms are normally overlooked. Here, we review the recent progress in MHBSs, focusing primarily on the mass/electron transfer regulation strategies for an enhanced microbial behavior. Specifically, the NMMs-regulated mass and electron transfer in extracellular, interfacial, and intracellular environment are summarized, where the patterns of diverse microbiological response are discussed thoroughly. Notably, fine modifications of cell interfaces and intracellular compartments by NMMs could even endow the biohybrids with new metabolic functions beyond their natural capabilities. Further, we also emphasize the importance of matching the various metabolic demands of biosystems with the diverse properties of NMMs to achieve efficient environmental remediation through a coordinated regulation strategy. Finally, major challenges and opportunities for the future development and practical implementation of MHBSs for environment remediation practices are given, aiming to provide future system design guidelines for attaining desirable biological behaviors.

The Application of Nano Zero-Valent Iron in Synergy with White Rot Fungi in Environmental Pollution Control

Developing efficient and sustainable pollution control technologies has become a research priority in the context of escalating global environmental pollution. Nano zero-valent iron (nZVI), with its high specific surface area and strong reducing power, demonstrates remarkable performance in pollutant removal. Still, its application is limited by issues such as oxidation, passivation, and particle aggregation. White rot fungi (WRF) possess a unique enzyme system that enables them to degrade a wide range of pollutants effectively, yet they face challenges such as long degradation cycles and low degradation efficiency. Despite the significant role of nZVI in pollutant remediation, most contaminated sites still rely on microbial remediation as a concurrent or ultimate treatment method to achieve remediation goals. The synergistic combination of nZVI and WRF can leverage their respective advantages, thereby enhancing pollution control efficiency. This paper reviews the mechanisms, advantages, and disadvantages of nZVI and WRF in pollution control, lists application examples, and discusses their synergistic application in pollution control, highlighting their potential in pollutant remediation and providing new insights for combined pollutant treatment. However, research on the combined use of nZVI and WRF for pollutant remediation is still relatively scarce, necessitating a deeper understanding of their synergistic potential and further exploration of their cooperative interactions.

Synergistic degradation of 2,4-dichlorophenoxyacetic acid in water by interfacial pre-reduction enhanced peroxymonosulfate activation derived from novel zero-valent iron/biochar

Iron-based biochar exhibits great potential in degrading emerging pollutants and remediation of water environments. In this study, a highly efficient catalytic Fe0/biochar (MZB-800) was synthesized by the co-pyrolysis of poplar sawdust and K2FeO4 at 800 °C. A novel water purification technology of pre-reduction followed by PMS activation for MZB-800 was proposed to degrade the refractory 2,4-dichlorophenoxyacetic acid (2,4-D) pesticide. The corrosive effect of the strong oxidizing potassium salt endowed the MZB-800 surface with more Fe0 and porous structure, achieving greater 2,4-D adsorption binding energy. The removal efficiency of MZB-800 on 2,4-D was greater than that of biochar (BC) and conventional Fe0/biochar (Fe-BC) prepared by FeCl3·6 H2O as the precursor. The proposed novel water purification technology showed the synergistic effect between the interfacial pre-reduction and the PMS activation derived by MZB-800. Regarding 2,4-D degradation and dechlorination performance, the synergistic coefficient between pre-reduction and subsequent PMS activation for MZB-800 were 2 and 1.4 respectively. Based on the normalized kinetic analysis and the Langmuir-Hinshelwood model, we proposed the underlying mechanism of MZB-800 interfacial pre-reduction and subsequent PMS activation for synergistic removal of 2,4-D. The large amount of Fe2+ and hydroxyl density accumulated by the Fe0 and hydroquinone structures on the MZB-800 surface during the pre-reduction stage provided abundant active sites for the subsequent activation of PMS. The improved activation reaction rate generated more reactive oxygen species, further strengthening the removal efficiency of 2,4-D. This work manifested that the novel water purification technology of pre-reduction/PMS activation of iron-based biochar is feasible for removing emerging pollutants in the water environment. ENVIRONMENTAL IMPLICATION: Extensive abuse of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide with high solubility and refractory degradation has caused environmental pollution and ecological deterioration. This manuscript described a novel water purification technology, centered on high-efficiency Fe0/biochar and utilizing pre-reduction and PMS reactivation strategies to synergistically degrade 2,4-D, which had strong environmental relevance. By elucidating the synergistic removal mechanism, the research provided valuable insights into removing emerging pollutants, thus promoting environmental sustainability and safeguarding ecosystem health. Overall, it is of high importance to provide a feasible and efficient method for removing hazardous 2,4-D from water environments, which contributes to addressing pressing environmental problems.

Enhancement of nitrogen on core taxa recruitment by Penicillium oxalicum stimulated microbially-driven soil formation in bauxite residue

Microbially-driven soil formation process is an emerging technology for the ecological rehabilitation of alkaline tailings. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. Herein, a 1-year field-scale experiment was applied to demonstrate the effect of nitrogen input on the structure and function of the microbiome in alkaline bauxite residue. Results showed that the contents of nutrient components were increased with Penicillium oxalicum (P. oxalicum) incorporation, as indicated by the increasing of carbon and nitrogen mineralization and enzyme metabolic efficiency. Specifically, the increasing enzyme metabolic efficiency was associated with nitrogen input, which shaped the microbial nutrient acquisition strategy. Subsequently, we evidenced that P. oxalicum played a significant role in shaping the assemblages of core bacterial taxa and influencing ecological functioning through intra- and cross-kingdom network analysis. Furthermore, a recruitment experiment indicated that nitrogen enhanced the enrichment of core microbiota (Nitrosomonas, Bacillus, Pseudomonas, and Saccharomyces) and may provide benefits to fungal community bio-diversity and microbial network stability. Collectively, these results demonstrated nitrogen-based coexistence patterns among P. oxalicum and microbiome and revealed P. oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. It will aid in promoting soil formation and ecological rehabilitation of bauxite residue. ENVIRONMENT IMPLICATION: Bauxite residue is a highly alkaline solid waste generated during the Bayer process for producing alumina. Attempting to transform bauxite residue into a stable soil-like substrate using low-cost microbial resources is a highly promising engineering. However, the dominant microorganisms and their specific roles in soil formation processes remain unknown. In this study, we evidenced the nitrogen-based coexistence patterns among Penicillium oxalicum and microbiome and revealed Penicillium oxalicum-mediated nutrient dynamics and ecophysiological adaptations in alkaline microhabitats. This study can improve the understanding of core microbes' assemblies that affect the microbiome physiological traits in soil formation processes.

The colonization of Penicillium oxalicum SL2 on rice root surface increased Pb interception capacity of iron plaque and decreased Pb uptake by roots

The exploration of microbial resources to reduce Pb accumulation in rice attracted great attention. In this study, we found Penicillium oxalicum SL2, a Pb-tolerant strain with good capability of dissolving phosphorus and stabilizing Pb in soil, was able to colonize on the root surface of rice seedlings without additional carbon sources, and promoted the secretion of metabolites related to amino acid metabolism, organic acid metabolism, signal transduction and other pathways in rhizosphere exudates, in which the secretion of oxalate increased by 47.7 %. However, P. oxalicum SL2 increased Fe(II) proportion and Fe availability on the root surface, resulting in iron plaque content decrease. Moreover, by converting root surface Pb from Pb-Fe state to PbC2O4 and Pb-P compounds, P. oxalicum SL2 increased Pb intercept capacity of iron plaque by 118.0 %. Furthermore, P. oxalicum SL2 regulated element distribution on the root surface, and reduced the relative content of Pb on the maturation zone of root tip, which was conducive to reducing Pb uptake by apoplastic pathway and the risk of Pb accumulation in root system. Our findings further revealed the interaction between P. oxalicum SL2 and rice root, providing a theoretical basis for the development and application of microbial agents in Pb-contaminated farmland.

Penicillium oxalicum SL2-enhanced nanoscale zero-valent iron effectively reduces Cr(VI) and shifts soil microbiota

Most current researches focus solely on reducing soil chromium availability. It is difficult to reduce soil Cr(VI) concentration below 5.0 mg kg-1 using single remediation technology. This study introduced a sustainable soil Cr(VI) reduction and stabilization system, Penicillium oxalicum SL2-nanoscale zero-valent iron (nZVI), and investigated its effect on Cr(VI) reduction efficiency and microbial ecology. Results showed that P. oxalicum SL2-nZVI effectively reduced soil total Cr(VI) concentration from 187.1 to 3.4 mg kg-1 within 180 d, and remained relatively stable at 360 d. The growth curve of P. oxalicum SL2 and microbial community results indicated that γ-ray irradiation shortened the adaptation time of P. oxalicum SL2 and facilitated its colonization in soil. P. oxalicum SL2 colonization activated nZVI and its derivatives, and increased soil iron bioavailability. After restoration, the negative effect of Cr(VI) on soil microorganisms was markedly alleviated. Cr(VI), Fe(II), bioavailable Cr/Fe, Eh, EC and urease (SUE) were the key environmental factors of soil microbiota. Notably, Penicillium significantly stimulated the growth of urease-positive bacteria, Arthrobacter, Pseudarthrobacter, and Microvirga, synergistically reducing soil chromium availability. The combination of P. oxalicum SL2 and nZVI is expected to form a green, economical and long-lasting Cr(VI) reduction stabilization strategy.