Improvement of tolerance to lead by filamentous fungus Pleurotus ostreatus HAU-2 and its oxidative responses

Metabolic perturbation and oxidative damage induced by tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and tris(2-ethylhexyl) phosphate (TEHP) on Escherichia coli through integrative analyses of metabolome

Organophosphate esters (OPEs) are one of the emerging environmental threats, causing the hazard to ecosystem safety and human health. Yet, the toxic effects and metabolic response mechanism after Escherichia coli (E.coli) exposed to TDCIPP and TEHP is inconclusive. Herein, the levels of SOD and CAT were elevated in a concentration-dependent manner, accompanied with the increase of MDA contents, signifying the activation of antioxidant response and occurrence of lipid peroxidation. Oxidative damage mediated by excessive accumulation of ROS decreased membrane potential and inhibited membrane protein synthesis, causing membrane protein dysfunction. Integrative analyses of GC-MS and LC-MS based metabolomics evinced that significant perturbation to the carbohydrate metabolism, nucleotide metabolism, lipids metabolism, amino acid metabolism, organic acids metabolism were induced following exposure to TDCIPP and TEHP in E.coli, resulting in metabolic reprogramming. Additionally, metabolites including PE(16:1(5Z)/15:0), PA(17:0/15:1(9Z)), PC(20:2(11Z,14Z)/12:0), LysoPC(18:3(6Z,9Z,12Z)/0:0) were significantly upregulated, manifesting that cell membrane protective molecule was afforded by these differential metabolites to improve permeability and fluidity. Overall, current findings generate new insights into the molecular toxicity mechanism by which E.coli respond to TDCIPP and TEHP stress and supply valuable information for potential ecological risks of OPEs on aquatic ecosystems.

Eco-friendly management of Meloidogyne incognita in cadmium-contaminated soil by using nematophagous fungus Purpureocillium lavendulum YMF1.683: Efficacy and mechanism

Root-knot nematodes (RKNs) are distributed globally, including in agricultural fields contaminated by heavy metals (HM), and can cause serious crop damages. Having a method that could control RKNs in HM-contaminated soil while limit HM accumulation in crops could provide significant benefits to both farmers and consumers. In this study, we showed that the nematophagous fungus Purpureocillium lavendulum YMF1.683 exhibited a high nematocidal activity against the RKN Meloidogyne incognita and a high tolerance to CdCl2. Comparing to the P. lavendulum YMF1.838 which showed low tolerance to Cd2+, strain YMF1.683 effectively suppressed M. incognita infection and significantly reduced the Cd2+ uptake in tomato root and fruit in soils contaminated by 100 mg/kg Cd2+. Transcriptome analyses and validation of gene expression by RT-PCR revealed that the mechanisms contributed to high Cd-resistance in YMF1.683 mainly included activating autophagy pathway, increasing exosome secretion of Cd2+, and activating antioxidation systems. The exosomal secretory inhibitor GW4869 reduced the tolerance of YMF1.683 to Cd2+, which firstly demonstrated that fungal exosome was involved in HM tolerance. The up-regulation of glutathione synthesis pathway, increasing enzyme activities of both catalase and superoxide dismutase also played important roles in Cd2+ tolerance of YMF1.683. In Cd2+-contaminated soil, YMF1.683 limited Cd2+-uptake in tomato by up-regulating the genes of ABCC family in favor of HM sequestration in plant, and down-regulating the genes of ZIP, HMA, NRAMP, YSL families associated with HM absorption, transport, and uptake in plant. Our results demonstrated that YMF1.683 could be a promising bio-agent in eco-friendly management of M. incognita in Cd2+ contaminated soils.

Synergy among extracellular adsorption, bio-precipitation and transmembrane transport of Penicillium oxalicum SL2 enhanced Pb stabilization

As a potential bioremediation strain for Pb contamination, Penicillium oxalicum SL2 sometimes has secondary activation of Pb, so it is crucial to clarify its effect on Pb morphology and its intracellular response to Pb stress. We investigated the effect of P. oxalicum SL2 in medium on Pb2+ and Pb availability in eight minerals, and revealed the prioritization of Pb products. (i)Pb was stabilized within 30 days as Pb3(PO4)2 or Pb5(PO4)3Cl with sufficient phosphorus (P); (ii) under P deficiency but sulfur (S) sufficient, Pb was stabilized mainly in the form of PbSO4; (iii) under conditions of P and S deficiency, Pb was stabilized mainly in the form of PbC2O2. With the help of proteomic and metabolomics analysis, a total of 578 different proteins and 194 different metabolites were found to be matched in 52 pathways. Among them, the activation of chitin synthesis, oxalate production, sulfur metabolism and transporters improved the Pb tolerance of P. oxalicum SL2, and promoted the synergistic effect of extracellular adsorption, bio-precipitation and transmembrane transport on Pb stabilization. Our results fill the gap in the intracellular response of P. oxalicum SL2 to Pb and provide new insights into the development of bioremediation agent and technology for Pb contamination.

An Approach to Evaluate Pb Tolerance and Its Removal Mechanisms by Pleurotus opuntiae

Widespread lead (Pb) contamination prompts various environmental problems and accounts for about 1% of the global disease burden. Thus, it has necessitated the demand for eco-friendly clean-up approaches. Fungi provide a novel and highly promising approach for the remediation of Pb-containing wastewater. The current study examined the mycoremediation capability of a white rot fungus, P. opuntiae, that showed effective tolerance to increasing concentrations of Pb up to 200 mg L−1, evidenced by the Tolerance Index (TI) of 0.76. In an aqueous medium, the highest removal rate (99.08%) was recorded at 200 mg L−1 whereas intracellular bioaccumulation also contributed to the uptake of Pb in significant amounts with a maximum of 24.59 mg g−1. SEM was performed to characterize the mycelium, suggesting changes in the surface morphology after exposure to high Pb concentrations. LIBS indicated a gradual change in the intensity of some elements after exposure to Pb stress. FTIR spectra displayed many functional groups including amides, sulfhydryl, carboxyl, and hydroxyl groups on the cell walls that led to binding sites for Pb and indicated the involvement of these groups in biosorption. XRD analysis unveiled a mechanism of biotransformation by forming a mineral complex as PbS from Pb ion. Further, Pb fostered the level of proline and MDA at a maximum relative to the control, and their concentration reached 1.07 µmol g−1 and 8.77 nmol g−1, respectively. High Pb concentration results in oxidative damage by increasing the production of ROS. Therefore, the antioxidant enzyme system provides a central role in the elimination of active oxygen. The enzymes, namely SOD, POD, CAT, and GSH, served as most responsive to clear away ROS and lower the stress. The results of this study suggested that the presence of Pb caused no visible adverse symptoms in P. opuntiae. Moreover, biosorption and bioaccumulation are two essential approaches involved in Pb removal by P. opuntiae and are established as worthwhile agents for the remediation of Pb from the environment.

Sodium alginate-based composite microspheres for controlled release of pesticides and reduction of adverse effects of copper in agricultural soils

Excessive copper (Cu) concentrations pose significant health risks to both plants and humans. In this study, sodium alginate (SA)-gelatin (GEL)-polyvinyl pyrrolidone (PVP)- embedded dinotefuran (DIN) microspheres were prepared using spray-drying technology. The loading content and encapsulation efficiency of optimal microspheres determined by physical modifications were 19.77% and 99.32%, respectively. In addition, the microspheres showed variable stimuli-responsive controlled release capacities in different temperatures and types of soil, as well as showed better control efficiency of larvae of Protaetia brevitarsis at pesticide application in the early stage, with the potential ability to control pest outbreaks at high temperatures. In addition, blank microspheres improved the growth and physiological activity of cucumber seedlings, reduced copper content in leaves, increased soil nutrient content, and prevented soil acidification. Further, the use of blank microspheres increased the relative abundance of soil beneficial functional bacteria communities, which mediate heavy metal (HM) immobilization/tolerance and promote plant growth. Redundancy analysis (RDA) and Spearman correlation analysis showed that these beneficial functional bacteria were mainly positively correlated with soil EC, A-N, and N-N. In summary, this study showed that the technique of combining physically modified carrier materials with pesticides has the potential to reduce Cu contamination in the surrounding agricultural soil during pesticide application, thereby reducing Cu uptake by crops.

Nitric oxide enhances resistance of Pleurotus eryngii to cadmium stress by alleviating oxidative damage and regulating of short-chain dehydrogenase/reductase family

The function and mechanism of nitric oxide (NO) in regulating Pleurotus eryngii biological response to cadmium (Cd) stress was evaluated by using anti-oxidation and short-chain dehydrogenase/reductase (SDR) family analysis. The fresh biomass of P. eryngii mycelia sharply decreased after treatment with 50 µM Cd; the lipid peroxidation and H₂O₂ accumulation in P. eryngii were found responsible for it. Proper exogenous supply of NO (150 µM SNP) alleviated the oxidative damage induced by Cd stress in P. eryngii, which reduced the accumulation of thiobarbituric acid reactive substances (TBARS) and H₂O₂. The activities of antioxidant enzymes (superoxide dismutase, peroxidase) were significantly increased to deal with Cd stress when treated with SNP (150 µM), and the content of proline was also closely related to NO-mediated reduction of Cd toxicity. Moreover, SDR family members were widely involved in the response to Cd stress, especially PleSCH70 gene was observed for the first time in participating in NO-mediated enhancement of Cd tolerance in P. eryngii. Taken together, this study provides new insights in understanding the tolerance mechanisms of P. eryngii to heavy metal and lays a foundation for molecular breeding of P. eryngii to improve its tolerance to environmental stress.

A novel yeast strain Geotrichum sp. CS-67 capable of accumulating heavy metal ions

Bioremediation, which has several advantages over traditional methods, represents an alternative means of dealing with heavy metal pollution. We screened for microorganisms showing heavy metal tolerance in polluted mangrove soils. A novel yeast, Geotrichum sp. CS-67, was discovered and tested for tolerance of Cu²⁺, Zn²⁺, and Ni²⁺. Zn²⁺ was the most efficiently sequestered by Geotrichum sp. CS-67 followed by Ni²⁺ and Cu²⁺. Zn²⁺ and Ni²⁺ were actively taken up into the cell, while Cu²⁺ was adsorbed to the cell wall. We used RNA-Seq to show that a large number of genes involved in the physiological and biochemical processing of heavy metals were differentially expressed in this yeast when it was subjected to Zn²⁺ and Ni²⁺ stress. From this panel, we selected the SED1, GDI1 and ZRT1 genes for validation by qRT-PCR and discovered that, during Zn²⁺ and Ni²⁺ stress, SED1 and GDI1 were upregulated, while ZRT1 was downregulated, which was consistent with the RNA-Seq results and the biochemical function of these genes. In conclusion, the novel yeast Geotrichum sp. CS-67 has a marked ability to accumulate heavy metal ions, making it of great interest as a possible microbial agent for heavy metal pollution remediation in the future.

Heavy metal-induced oxidative stress and alteration in secretory proteins in yeast isolates

In the recent years, yeasts have evolved as potent bioremediative candidates for the detoxification of xenobiotic compounds found in the natural environment. Candida sp. are well-studied apart from Saccharomyces sp. in heavy metal detoxification mechanisms. In the current study, Candida parapsilosis strain ODBG2, Candida sp. strain BANG3, and Candida viswanathii strain ODBG4 were isolated from industrial effluents and contaminated ground water, and were studied for their metal tolerance. Among these three isolates, the metal tolerance was found to be more towards Lead (Pb 2 mM), followed by Cadmium (Cd 1.5 mM) and Chromium [Cr(VI), 1 mM]. On further exploring the involvement of primary defensive enzymes in these isolates towards metal tolerance, the anti-oxidative enzyme superoxide dismutase was found to be prominently high (25% with respect to the control) during first 24 h of metal-isolate interaction. The Catalase enzyme assay was observed to have increased enzyme activity at 48 h. It also triggered the activity of peroxidases, which lead to the increase in reduced glutathione in the organism by 0.87-1.9-fold as a metal chelator and also as a second-line defensive molecule. The exoproteome profile showed the early involvement (exponential growth phase) of secreted proteins (low-molecular-weight) of about ~ 40-45 kDa under Cd and Pb stress (0.5 mM). The exoproteome profiling under heavy metal stress in Candida parapsilosis strain ODBG2 and Candida viswanathii strain ODBG4 is the first report.

Heavy metal fixation of lead-contaminated soil using Morchella mycelium

With the exploitation of lead-zinc deposits, lead content around mining areas has seriously exceeded the recommended level. The most challenging problem is how to reduce lead contamination in soil efficiently. In this study, we developed a method to remediate lead-contaminated soil by adding Morchella mycelium. First, we compared the repair effects of mycelium and hyperaccumulator by conducting pot experiments. Then, we investigated the mechanism through which mycelium repairs lead-contaminated soil by conducting simulation experiments. Results showed that using mycelium was a more efficient way to repair soil than using hyperaccumulator. Compared with the untreated group, mycelium reduced the lead content of crops by 34.83 % and raised dry biomass by 134.05 % when lead addition was 800 mg/kg. After mycelium fixation, soil catalase, urease, cellulase, and sucrase activities were significantly enhanced, and the bioavailability of lead decreased significantly. The lead solution exposure simulation test showed that Morchella mycelium immobilized lead due to its extracellular secretions. That is, mycelium secreted metabolites and lead to form salt crystals, reducing bioavailable lead content. In addition, Morchella mycelium restoration may effectively improve soil fertility and increase crop yields. Thus, mycelium may be used successfully in alternative green repair methods for environmental heavy metal remediation.

Morphological changes and bioaccumulation in response to cadmium exposure in Morchella spongiola, a fungus with potential for detoxification

Morchella is a genus of edible fungi with strong resistance to Cd and the ability to accumulate it in the mycelium. However, the mechanisms conferring Cd resistance in Morchella are unknown. In the present study, morphological and physiological responses to Cd were evaluated in the mycelia of Morchella spongiola. Variations in hyphal micro-morphology including twisting, folding and kinking in mycelia exposed to different Cd concentrations (0.15, 0.9, 1.5, 2.4, 5.0 mg/L) were observed using scanning electron microscopy. Deposition of Cd precipitates on cell surfaces (at Cd concentrations > 2.4 mg/L) was shown by SEM-EDS. Transmission electron microscopy analysis of cells exposed to different concentrations of Cd revealed the loss of intracellular structures and the localization of Cd depositions inside/outside the cell. FTIR analysis showed that functional groups such as C=O, -OH, -NH and -CH could be responsible for Cd binding on the cell surface of M. spongiola. In addition, intracellular accumulation was observed in cultures at low Cd concentrations (< 0.9 mg/L), while extracellular adsorption occurred at higher concentrations. These results provide valuable information on the Cd tolerance mechanism in M. spongiola and constitute a robust foundation for further studies on fungal bioremediation strategies.

Mycoremediation of heavy metals: processes, mechanisms, and affecting factors

Industrial processes and mining of coal and metal ores are generating a number of threats by polluting natural water bodies. Contamination of heavy metals (HMs) in water and soil is the most serious problem caused by industrial and mining processes and other anthropogenic activities. The available literature suggests that existing conventional technologies are costly and generated hazardous waste that necessitates disposal. So, there is a need for cheap and green approaches for the treatment of such contaminated wastewater. Bioremediation is considered a sustainable way where fungi seem to be good bioremediation agents to treat HM-polluted wastewater. Fungi have high adsorption and accumulation capacity of HMs and can be potentially utilized. The most important biomechanisms which are involved in HM tolerance and removal by fungi are bioaccumulation, bioadsorption, biosynthesis, biomineralisation, bioreduction, bio-oxidation, extracellular precipitation, intracellular precipitation, surface sorption, etc. which vary from species to species. However, the time, pH, temperature, concentration of HMs, the dose of fungal biomass, and shaking rate are the most influencing factors that affect the bioremediation of HMs and vary with characteristics of the fungi and nature of the HMs. In this review, we have discussed the application of fungi, involved tolerance and removal strategies in fungi, and factors affecting the removal of HMs.

Use of soil fungi in the biosorption of three trace metals (Cd, Cu, Pb): promising candidates for treatment technology?

Trace metal contamination is a widespread and complex environmental problem. Because fungi are capable of growing in adverse environments, several fungal species could have an interesting potential in remediation technologies for metal contaminated environments. This study proposes to test the ability to tolerate and biosorb three trace metals (Cd, Cu and Pb) of 28 fungal isolates collected from different soils. First, a tolerance assay in agar medium was performed. Each isolate was grown in the presence of Cd, Cu, and Pb at different concentrations. Then, we exposed each soil fungus to 50 mg L^-1 of Cd, Cu, or Pb during 3 days in liquid medium. Parameters such as biomass production, pH, and biosorption were evaluated. The results showed that responses to metal exposure are very diverse even with fungi isolated from the same soil sample, or belonging to the same genera. Several isolates could be considered as good metal biosorbents and could be used in future mycoremediation studies. Among the 28 fungi tested, Absidia cylindrospora biosorbed more than 45% of Cd and Pb, Chaetomium atrobrunneum biosorbed more than 45% of Cd, Cu, Pb, and Coprinellus micaceus biosorbed 100% of Pb.

Modular engineering of Shiraia bambusicola for hypocrellin production through an efficient CRISPR system

Shiraia bambusicola exhibits an excellent capability to produce high-value pharmacological drugs, such as hypocrellin. However, less effective molecular tools hamper the processes to discover or exploit these metabolites. To address this issue, the more effective CRISPR/Cas9 system was constructed by optimizing the sgRNA transcription elements and disrupting the endogenous non-homologous end-joining pathway. These tactics prompted the gene-targeting frequency of 100% and simultaneously multiplex genome editing in S. bambusicola. This optimal CRISPR system encouraged us to rewire the entire hypocrellin flux and improve the yield by orchestrating the substrate pool supply, the central hypocrellin pathway, and the antioxidant system. Thus, 8632 mg/L hypocrellin was obtained, resulting in a 12-fold increase than that of the wild-type strain. This engineered S. bambusicola can still endure oxidative stresses from higher target metabolites and sustain an excellent biological activity. This study provides a whole conception to establish the more efficient genome-editing system. Higher conserved transcription elements for sgRNA expressions inspire us to adopt this system for gene modifications of other filamentous fungi. The rational and global biosystems outline will offer guidance to modulate metabolite productivity in other filamentous fungi.

Lead, cadmium and nickel removal efficiency of white-rot fungus Phlebia brevispora

Widespread of heavy metals contamination has led to several environmental problems. Some biological methods to remove heavy metals from contaminated wastewater are being widely explored. In the present study, the efficiency of a white-rot fungus, Phlebia brevispora to remove different metals (Pb, Cd and Ni) has been evaluated. Atomic absorption spectroscopy of treated and untreated metal containing water revealed that all the metals were efficiently removed by the fungus. Among all the used metals, cadmium was the most toxic metal for fungal growth. Phlebia brevispora removed maximum Pb (97·5%) from 100 mmol l^-1 Pb solution, which was closely followed by Cd (91·6%) and Ni (72·7%). Scanning electron microscopic images revealed that the presence of metal altered the morphology and fine texture of fungal hyphae. However, the attachment of metal on mycelia surface was not observed during energy-dispersive X-ray analysis, which points towards the intracellular compartmentation of metals in vacuoles. Thus, the study demonstrated an application of P. brevispora for efficient removal of Pb, Cd and Ni from the metal contaminated water, which can further be applied for bioremediation of heavy metals present in the industrial effluent.

Removal mechanism of Pb(II) by Penicillium polonicum: immobilization, adsorption, and bioaccumulation

Currently, lead (Pb) has become a severe environmental pollutant and fungi hold a promising potential for the remediation of Pb-containing wastewater. The present study showed that Penicillium polonicum was able to tolerate 4 mmol/L Pb(II), and remove 90.3% of them in 12 days through three mechanisms: extracellular immobilization, cell wall adsorption, and intracellular bioaccumulation. In this paper. the three mechanisms were studied by Raman, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results indicated that Pb(II) was immobilized as lead oxalate outside the fungal cell, bound with phosphate, nitro, halide, hydroxyl, amino, and carboxyl groups on the cell wall, precipitated as pyromorphite [Pb₅(PO₄)₃Cl] on the cell wall, and reduced to Pb(0) inside the cell. These combined results provide a basis for additionally understanding the mechanisms of Pb(II) removal by P. polonicum and developing remediation strategies using this fungus for lead-polluted water.

Hexavalent chromium stress response, reduction capability and bioremediation potential of Trichoderma sp. isolated from electroplating wastewater

In the present study we are investigating the Cr_(VI) reduction potential of a multi-metal tolerant fungus (isolate CR700); isolated from electroplating wastewater. Based on the ITS region sequencing, the isolate was identified as Trichoderma lixii isolate CR700 and able to tolerate As(2000 mg/L), Ni(1500 mg/L), Zn(1200 mg/L), Cu(1200 mg/L), Cr(1000 mg/L), and 100 mg/L of Pb and Cd evident from tolerance assay. Cr_(VI) reduction experiment was conducted in Erlenmeyer flasks containing different concentration of Cr_(VI) (0-200 mg/L) amended potato dextrose broth medium followed by inoculating with a disk (0.5 cm diameter) of 7 days grown isolate CR700, and achieved a maximum of 99.4% within 120 h at 50 mg/L of Cr_(VI). However, the accumulation of total Cr by isolate CR700 was 2.12 ± 0.15 mg/g of dried biomass at the same concentration after 144 h of exposure. Isolate CR700 showed the capability to reduce Cr_(VI) at different physicochemical stress conditions such as pH, temperature, heavy metals, metabolic inhibitor and also in tannery wastewater. Fungus exhibited multifarious morphological and biochemical response under the exposure of Cr_(VI); the scanning electron microscopic analysis revealed that Cr_(VI) treated mycelia of isolate CR700 comparatively irregular, aggregated and swelled than without treated mycelia which might be due to the tolerance mechanism and vacuolar compartmentation of chromium. Moreover, energy dispersive spectroscopy and x-ray photoelectron spectroscopic analysis exposed the Cr_(III) precipitation on the mycelia surface of isolate CR700 and Fourier-transform infrared spectroscopic analysis suggested the contribution of the protein associated functional group in the complexation of Cr_(VI). The phytotoxicity test of fungal treated 100 mg/L of Cr_(VI) supernatant on Vigna radiata and Cicer arietinum revealed the successful detoxification/remediation of Cr_(VI).

Removal and tolerance mechanism of Pb by a filamentous fungus: A case study

Currently, Pb pollution has become a severe environmental problem and filamentous fungi hold a promising potential for the treatment of Pb-containing wastewater. The present study showed that the strain Pleurotus ostreatus ISS-1 had a strong ability to tolerate Pb at high concentration and reached a removal rate of 53.7% in liquid media. Pb was removed by extracellular biosorption, intracellular bioaccumulation by mycelia, or precipitation with extracellular oxalic acids. On the cellular level, Pb was mainly distributed in the cell wall, followed by vacuoles and organelles. Fourier transform infrared spectroscopy (FTIR) analysis indicated that hydroxyl, amides, carboxyl, and sulfhydryl groups provided binding sites for Pb. Furthermore, Pb was found on the cell surface in the form of PbS and PbCO₃ through X-ray diffraction (XRD). Intracellular chelates such as thiol compounds and oxalic acid, as well as extracellular oxalic acid, might play an important role in the tolerance of Pb. In addition, isobaric tags for relative and absolute quantitation (iTRAQ) analysis showed that ATP-binding cassette (ABC) transporter, cytochrome P450, peroxisome, and the calcium signaling pathway might participate in both accumulation and detoxification of Pb. These results have successfully provided a basis for further developing Pb polluted water treatment technology by fungi.

Antioxidant defenses at enzymatic and transcriptional levels in response to acute lead administration in Oxya chinensis

Lead (Pb) is known to be toxic to many organisms. Oxidative stress is a major mechanism of its toxicity. This research aims to investigate the effects of Pb on hydrogen peroxide (H₂O₂) and malonedialdehyde (MDA) contents, activities and mRNA levels of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)) after Oxya chinensis were acutely treated with lead acetate for 24 h. The results showed that the LD₅₀-24 h value of lead acetate to O. chinensis was 1541.89 (1431.19-1655.77) μg g^-1 body H₂O₂ and MDA contents were elevated after Pb administration, which suggested that Pb induced the overproduction of ROS and caused oxidative stress. SOD activities were significantly inhibited 40.42% of the control by 280 μg μL^-1 Pb. CAT activities were increased while GPx activities had no significant changes. Different types of antioxidant-related genes had various responses to Pb stress. The transcriptions of icCuZnSOD2 and ecCuZnSOD2 were significantly inhibited by different concentrations of Pb. MnSOD mRNA levels showed the concentration-dependent rise with the Pb concentrations increase. The expressions of ecCuZnSOD1, CAT1, and GPx were significantly up-regulated while the transcriptions of icCuZnSOD1 and CAT2 had no significant changes. Alteration of activities and mRNA expressions of antioxidant enzymes implied that Pb-induced antioxidant defenses were related to modifications at enzymatic and transcriptional levels. The profiles of antioxidant enzymes and H₂O₂ and MDA contents and relationships among the parameters indicated that the cooperation of multiple antioxidants rather than a single factor might be responsible for the antioxidant defenses against Pb stress.

Mechanisms of Cr(VI) resistance by endophytic Sphingomonas sp. LK11 and its Cr(VI) phytotoxic mitigating effects in soybean (Glycine max L.)

Chromium Cr(VI) is highly toxic and leads to impaired phenotypic plasticity of economically important crops. The current study assessed an endophytic-bacteria assisted metal bio-remediation strategy to understand stress-alleviating mechanisms in Glycine max L (soybean) plants inoculated with Sphingomonas sp. LK11 under severe Cr(VI) toxicity. The screening analysis showed that high Cr concentrations (5.0 mM) slightly suppressed LK11 growth and metal uptake by LK11 cells, while significantly enhancing indole-3-acetic acid (IAA) production. Endophytic LK11 significantly upregulated its antioxidant system compared to control by enhancing reduced glutathione (GSH), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities to counteract Cr-induced oxidative stress. Cr toxicity induced cell morphological alteration, as shown by SEM-EDX analysis and triggered significant lipid peroxidation. The interaction between LK11 and soybean in Cr-contaminated soil significantly increased plant growth attributes and down-regulated the synthesis of endogenous defense-related phytohormones, salicylic acid and abscisic acid, by 20% and 37%, respectively, and reduced Cr translocation to the roots, shoot, and leaves. Additionally, Cr-induced oxidative stress was significantly reduced in LK11-inoculated soybean, regulating metal responsive reduced GSH and enzymatic antioxidant CAT. Current findings indicate that LK11 may be a suitable candidate for the bioremediation of Cr-contaminated soil and stimulation of host physiological homeostasis.

Investigation of lead bioimmobilization and transformation by Penicillium oxalicum SL2

Fungi Penicillium oxalicum SL2 was applied for Pb²⁺ bioremediation in aqueous solution in this study. After 7 days of incubation at different initial concentrations of Pb²⁺ (0, 100, 500 and 2500 mg L^-1), most of Pb²⁺ were removed (90, 98.3, and 86.2%), the maximum Pb content in mycelium reached about 155.6 mg g^-1 dw. Meanwhile, the formation of extracellular secondary minerals and intracellular Pb-complex were observed and identified, the speciation of Pb in mycelium was also detected by X-ray absorption near-edge structure (XANES) spectroscopy, i.e., Pb-oxalate, Pb-citrate, Pb-hydrogen phosphate and Pb-glutathione analogues. In addition, content of glutathione and oxidized glutathione was increased under the exposure of Pb²⁺, which implied that glutathione might play a key role in Pb immobilization and detoxification in P. oxalicum SL2. This study elucidated partial mechanisms of Pb immobilization and speciation transformation of this strain, providing an alternative biomaterial in the bioremediation of Pb-contaminated wastewater.

Cd resistant characterization of mutant strain irradiated by carbon-ion beam

Heavy metal pollution is harmful to the environment and to human health. Resistant strains can grow in adverse conditions and store heavy metals to reduce their damage. The Cd²⁺ resistant mutant strain C2, which was irradiated by the ¹²C⁶⁺ beams, can grow in Cd medium ranging from 20 to 100 mg L^-1 when compared with the original strain. Attempting to discern the cause of the resistance, the phenotype and antioxidant defense system were analyzed. SEM images showed that when exposed to Cd²⁺, gaps on the cell surface were filled with a complex granular compound. FT-IR demonstrated that the alcoholic hydroxyl group, amino, and amide groups combined with ions. Moreover, responses of antioxidant defense system were different in the Cd²⁺ groups. The expression of SOD peaked at 24 h in high concentrations of Cd²⁺; the content of GSH increased gradually and was significantly affected by cultivation time. The MDA and CAT had the strongest response to 20 mg L^-1 Cd²⁺, and the related metabolic pathway of CAT might play a key role in the resistance to high concentrations of Cd²⁺. The result indicated that the applicability of C2 could provide potential biotechnology for treatment of wastewaters and soils with Cd pollutions.

Comparative Assessment of the Bioremedial Potentials of Potato Resistant Starch-Based Microencapsulated and Non-encapsulated Lactobacillus plantarum to Alleviate the Effects of Chronic Lead Toxicity

Lead (Pb) is a well-recognized and potent heavy metal with non-biodegradable nature and can induce the oxidative stress, degenerative damages in tissues, and neural disorders. Certain lactic acid bacterial strains retain the potential to mitigate the lethal effects of Pb. The present work was carried out to assess the Pb bio-sorption and tolerance capabilities of Lactobacillus plantarum spp. Furthermore, potato resistant starch (PRS)-based microencapsulated and non-encapsulated L. plantarum KLDS 1.0344 was utilized for bioremediation against induced chronic Pb toxicity in mice. The experimental mice were divided into two main groups (Pb exposed and non-Pb exposed) and, each group was subsequently divided into three sub groups. The Pb exposed group was exposed to 100 mg/L Pb(NO₃)₂ via drinking water, and non-Pb exposed group was supplied with plain drinking water during 7 weeks prolonged in vivo study. The accumulation of Pb in blood, feces, renal, and hepatic tissues and its pathological damages were analyzed. The effect of Pb toxicity on the antioxidant enzyme capabilities in blood, serum, as well as, on levels of essential elements in tissues was also calculated. Moreover, KLDS 1.0344 displayed remarkable Pb binding capacity 72.34% and Pb tolerance (680 mg/L). Oral administration of both non- and PRS- encapsulated KLDS 1.0344 significantly provided protection against induced chronic Pb toxicity by increasing fecal Pb levels (445.65 ± 22.28 μg/g) and decreasing Pb in the blood up to 137.63 ± 2.43 μg/L, respectively. KLDS 1.0344 microencapsulated with PRS also relieved the renal and hepatic pathological damages and improved the antioxidant index by inhibiting changes in concentrations of glutathione peroxidase, glutathione, superoxide dismutase, malondialdehyde, and activated oxygen species, which were affected by the Pb exposure. Overall, our results suggested that L. plantarum KLDS 1.0344 either in free or encapsulated forms hold the potentiality to deliver a dietetic stratagem against Pb lethality.

Cadmium-induced stress response of Phanerochaete chrysosporium during the biodegradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47)

Cd-induced stress response of Phanerochaete chrysosporium during the biodegradation of BDE-47 was investigated in this study, with the goal of elucidating the tolerance behavior and the detoxification mechanisms of P. chrysosporium to resist the Cd stress in the course of BDE-47 biodegradation, which has implications for expanding the application of P. chrysosporium in the bioremediation of Cd and BDE-47 combined pollution. The results suggested that single BDE-47 exposure did not induce obvious oxidative stress in P. chrysosporium, but coexistent Cd significantly triggered ROS generation, both intracellular ROS level and H₂O₂ content showed positive correlation with Cd concentration. The activities of SOD and CAT were enhanced by low level of Cd (≤ 1 mg/L), but Cd of higher doses (＞1 mg/L) depressed the expression of these two antioxidant enzymes at the later exposure period (3-5 days). The intracellular content of GSH along with GSH/GSSG ratio also exhibited a bell-shaped response with a maximum value at Cd of 1 mg/L. Furthermore, Cd-induced ROS generation resulted in the lipid peroxidation, as indicated by a noticeable increment of MDA content found after 3 days. Moreover, the study also indicated that Cd less than 1 mg/L promoted the production of extracellular protein and quickened the decrease of pH value in the medium, while excessive Cd (＞1 mg/L) would lead to inhibition. These findings obtained demonstrated that P. chrysosporium had a certain degree of tolerance to Cd within a specific concentration range via regulating the antioxidant levels, inducing the synthesis of extracellular protein as well as stimulating the production of organic acids, and 1 mg/L is suggested to be the tolerance threshold of this strains under Cd stress during BDE-47 biodegradation.

Enhanced immobilization of U(VI) on Mucor circinelloides in presence of As(V): Batch and XAFS investigation

The combined pollution of radionuclides and heavy metals has been given rise to widespread concern during uranium mining. The influence of As(V) on U(VI) immobilization by Mucor circinelloides (M. circinelloides) was investigated using batch experiments. The activity of antioxidative enzymes and concentrations of thiol compounds and organic acid in M. circinelloides increased to respond to different U(VI) and As(V) stress. The morphological structure of M. circinelloides changed obviously under U(VI) and As(V) stress by SEM and TEM analysis. The results of XANES and EXAFS analysis showed that U(VI) was mainly reduced to nano-uraninite (nano-UO₂, 30.1%) in U₄₀₀, while only 9.7% of nano-UO₂ was observed in the presence of As(V) in U₄₀₀-As₄₀₀ due to the formation of uranyl arsenate precipitate (Trögerite, 48.6%). These observations will provide the fundamental data for fungal remediation of uranium and heavy metals in uranium-contaminated soils.

Hydrogen-rich water alleviates the toxicities of different stresses to mycelial growth in Hypsizygus marmoreus

In plants, hydrogen gas (H₂) enhances tolerance to several abiotic stresses, including salinity and heavy metals. However, the effect of H₂ on fungal growth under different stresses remains largely unclear. In this study, hydrogen-rich water (HRW) was employed to characterize physiological roles and molecular mechanisms of H₂ in the alleviation of three different stresses in basidiomycete Hypsizygus marmoreus. Our results showed that HRW treatment, of which the H₂ concentration was 0.8 mM, significantly reduced the toxicities of CdCl₂, NaCl and H₂O₂, leading to significantly improved mycelial growth and biomass. These beneficial effects could be attributed to a significantly decreased formation of malondialdehyde (MDA). Besides, HRW treatment significantly increased the activities of antioxidants (SOD, CAT and GR) as well as the gene expressions of these antioxidants (SOD, CAT, and GR) at the mRNA level. In vivo detection of reactive oxygen species (ROS), including H₂O₂ and O₂⁻, as well as lipid peroxidation provided further evidence that HRW could significantly improve tolerances of CdCl₂, NaCl and H₂O₂. Furthermore, pyruvate kinase was activated in the mycelia treated with HRW, along with its induced gene expression, suggesting that HRW treatment enhanced the glucose metabolism. Taken together, our findings suggested that the usage of HRW could be an effective approach for contaminant detoxification in H. marmoreus, which was similar with the effects of HRW in plants, and such effects could be also beneficial in entire agricultural system.

Lead-induced oxidative stress and antioxidant response provide insight into the tolerance of Phanerochaete chrysosporium to lead exposure

The present work investigated the effect of lead (Pb) on the growth, metal accumulation, oxidative stress, and antioxidant response in Phanerochaete chrysosporium, which is a well-known hyperaccumulating species for heavy metal with appreciable bioaccumulation capacity. Results revealed that P. chrysosporium exhibited a good ability in Pb accumulation and tolerance over a concentration range of 50-100 mg L^-1 Pb. The removal rate of Pb decreased with the increasing levels of Pb and reached a maximum of 91.3% at 50 mg L^-1. Both extracellular adsorption and intracellular bioaccumulation contributed to the removal of Pb, with the maximum of 123.8 mg g^-1 and 162.5 mg g^-1 dry weight, respectively. Pb may exert its toxicity to P. chrysosporium by impairing oxidative metabolism, as evidenced by the enhanced accumulation of hydrogen peroxide (H₂O₂) and lipid peroxidation product malonaldehyde (MDA). P. chrysosporium evolved an antioxidant system by elevating the activity of superoxide dismutase (SOD) and the level of reduced glutathione (GSH) in response to Pb stress, whereas decreasing the activities of catalase (CAT) and peroxidase (POD). Moreover, Pearson correlation analysis demonstrated a good correlation between oxidative stress biomarkers and enzymatic antioxidants. The preset work suggested that P. chrysosporium exhibited an outstanding accumulation of Pb and tolerance of Pb-induced oxidative stress by the effective antioxidant defense mechanism.

Hexavalent chromium induced oxidative stress and apoptosis in Pycnoporus sanguineus

White rot fungi have been proved to be a promising option for the removal of heavy metals, understanding their toxic response to heavy metals is conducive to developing and popularizing fungi-based remediation technologies so as to lessen the hazard of heavy metals. In this study, Cr(VI)-induced oxidative stress and apoptosis in Pycnoporus sanguineus, a species of white rot fungi were investigated. The results suggested that high level of Cr(VI) promoted the formation of ROS, including H₂O₂, O₂^•- and ·OH. With the increment of Cr(VI) concentration, the SOD and CAT activity along with GSH content increased within the first 24 h, but decreased afterward, companied with a significant enhancement of MDA content. Cr(VI)-induced oxidative damage further caused and aggravated apoptosis in P. sanguineus, especially at Cr(VI) concentrations above 20 mg/L. Cr(VI)-induced apoptosis was involved with mitochondrial dysfunction including mitochondrial depolarization, the enhancement of mitochondrial permeability and release of cytochrome c. The early and late apoptosis hallmarks, such as metacaspase activation, phosphatidylserine (PS) externalization, DNA fragmentation and the nuclear condensation and fragmentation were observed. Moreover, we also found disturbances of ion homeostasis, which was featured by K⁺ effluxes and overload of cytoplasmic and mitochondrial Ca²⁺.Based on these results, we suggest that Cr(VI) induced oxidative stress and apoptosis in white rot fungi, P. sanguineus.

Mechanisms of Cd and Cr removal and tolerance by macrofungus Pleurotus ostreatus HAU-2

Fungi bioaccumulation is a novel and highly promising approach to remediate polluted soil. The present study revealed a high ability to tolerate Cd and Cr in the fungus Pleurotus ostreatus HAU-2. However, high concentrations of Cd and Cr can suppress fungal growth and result in a variation of hypha micromorphology. Batch experiments were performed to investigate Cd and Cr stress effects on the amount of active oxygen in fungi, activity of antioxidant enzyme, as well as the removal efficiency of Cd and Cr. The results revealed that Cd and Cr caused increasing active oxygen and malonaldehyde (MDA) concentrations. Antioxidant enzymes play a central role in removing active oxygen, while glutathione (GSH) aids the Cd detoxification within cells. In fluid culture, fungal removal rates of Cd and Cr ranged from 44.85% to 80.36% and 14.49% to 45.55%, respectively. Intracellular accumulation and extracellular adsorption were the major removal approaches. Bag cultivation testing indicated that the fungus absorbed Cd and Cr contained within soil. In particular, the accumulation ability of Cd (15.6mgkg^-1) was higher compared to that of Cr (8.9mgkg^-1). These results successfully establish P. ostreatus HAU-2 as promising candidate for the remediation of heavy-metal polluted soils.