Cd Bioremediation Research Articles

Simultaneous removal of cadmium and arsenic co-contamination by iron/sulfur-modified zeolites combined with sulfate-reducing bacteria

As common water environmental pollutants, the problem of co-contamination of cadmium (Cd) and arsenic (As) has aroused widespread concern. To solve the problem, microbial remediation technology, represented by its high efficiency, cheapness, and stability, has gained increased attention. In this study, we conducted an investigation on the efficacy of Fe/S modified zeolites (Z-FeOS) and sulfate-reducing bacteria (SRB) in removing Cd(II) and As(III) contained wastewater. The Cd(II) and As(III) removal efficacy of Z-FeOS+SRB were investigated by differing the addition time of heavy metals, SRB dosage, Z-FeOS dosage, pH, and reaction time. The produced precipitates were characterized to elucidate the removal mechanism. The results showed that the removal efficiency of Z-FeOS+SRB was much better than that of separate Z-FeOS and SRB treatments. At the Cd(II) and As(III) concentrations of 10 and 5 mg/L, respectively, the ideal removal conditions of Z-FeOS+SRB were post-heavy metal addition time of 48 h, SRB dosage of 20 % v/v, Z-FeOS dosage of 0.7 % m/v, pH 8.0, and reaction time of 168 h. Under these conditions, Cd(II) and As(III) removal efficiencies were 93.4 % and 39.9 %, respectively. The characterization results illustrated the existence of CdS and As2S3 in the precipitation products, suggesting that Cd and As were removed through sorption/co-precipitation in these forms. This study demonstrated the application potential of Z-FeOS+SRB in the bioremediation of Cd and As from environments.

Unlocking Cd(II) biosorption potential of Candida tropicalis XTA 1874 for sustainable wastewater treatment

Cd(II) is a potentially toxic heavy metal having carcinogenic activity. It is becoming widespread in the soil and groundwater by various natural and anthropological activities. This is inviting its immediate removal. The present study is aimed at developing a Cd(II) resistant strain isolated from contaminated water body and testing its potency in biological remediation of Cd(II) from aqueous environment. The developed resistant strain was characterized by SEM, FESEM, TEM, EDAX, FT-IR, Raman Spectral, XRD and XPS analysis. The results depict considerable morphological changes had taken place on the cell surface and interaction of Cd(II) with the surface exposed functional groups along with intracellular accumulation. Molecular contribution of critical cell wall component has been evaluated. The developed resistant strain had undergone Cd(II) biosorption study by employing adsorption isotherms and kinetic modeling. Langmuir model best fitted the Cd(II) biosorption data compared to the Freundlich one. Cd(II) biosorption by the strain followed a pseudo second order kinetics. The physical parameters affecting biosorption were also optimized by employing response surface methodology using central composite design. The results depict remarkable removal capacity 75.682 ± 0.002% of Cd(II) by the developed resistant strain from contaminated aqueous medium using 500 ppm of Cd(II). Quantitatively, biosorption for Cd(II) by the newly developed resistant strain has been increased significantly (p < 0.0001) from 4.36 ppm (non-resistant strain) to 378.41 ppm (resistant strain). It has also shown quite effective desorption capacity 87.527 ± 0.023% at the first desorption cycle and can be reused effectively as a successful Cd(II) desorbent up to five cycles. The results suggest that the strain has considerable withstanding capacity of Cd(II) stress and can be employed effectively in the Cd(II) bioremediation from wastewater.

In vitro exploration of Acinetobacter strain (SG-5) for antioxidative potential and phytohormone biosynthesis in maize (Zea mays L.) cultivars differing in cadmium tolerance.

Cadmium (Cd) poses serious threats to plant growth and development, whereas the use of plant growth-promoting rhizobacteria (PGPR) has emerged a promising approach to diminish Cd retention in crops. A pot experiment was conducted to evaluate the effect of Cd tolerant strain Acinetobacter sp. SG-5 on growth, phytohormonal response, and Cd uptake of two maize cultivars (3062 and 31P41) under various Cd stress levels (0, 5, 12, 18, 26, and 30μM CdCl2). The results revealed that CdCl2 treatment significantly suppressed the seed germination and growth together with higher Cd retention in maize cultivars in a dose-dependent and cultivar-specific manner with pronounced negative effect in 31P41. However, SG-5 strain exerted positive impact by up-regulating seed germination traits, plant biomass, photosynthetic pigments, enzymatic and non-enzymatic antioxidants, endogenous hormone level indole-3-acetic acid (IAA), abscisic acid (ABA), and sustained optimal nutrient's levels in both cultivars but predominantly in Cd-sensitive one (31P41). Further, Cd-resistant PGPR decreased the formation of reactive oxygen species in terms of malondialdehyde (MDA) and hydrogen peroxide (H2O2) verified through 3, 3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) analysis in conjunction with reduced Cd uptake and translocation in maize root and shoots in comparison to controls, advocating its sufficiency for bacterial-assisted Cd bioremediation. In conclusion, both SG-5 inoculated cultivars exhibited maximum Cd tolerance but substantial Cd tolerance was acquired by Cd susceptible cultivar-31P41 than Cd-tolerant one (3062). Current work recommended SG-5 strain as a promising candidate for plant growth promotion and bacterial-assisted phytomanagement of metal-polluted agricultural soils.

Enhancing remediation efficiency of hyperaccumulators through earthworm addition: Evidence from a pot study on cadmium-contaminated soil

Soil cadmium (Cd) contamination is an urgent environmental problem, which endangers human health through the food chain. Bioremediation attracted extensive attention around the world due to the high cost-efficiency. However, the remediation efficiency of different plant and earthworm species of soil Cd pollution is still unclear, it is thus of great significance to explore the combined effects of different remediation plants and earthworm species to improve the bioremediation capacity. In the present study, we consequently selected three species of Cd hyperaccumulator plants (vetiver, P. vittata and S. emarginatum) and three species of earthworms (E. fetida P1, E. fetida P2, and P. guillelmi) to compare the differences in Cd accumulation among various earthworm-plant combinations. Results indicated that the changes of soil pH and SOM in plant-animal combined application induced the higher soil Cd removal efficiency. The Cd removal efficiency showed highest in combination groups P. vittata-E. fetida P2 and P. vittata-P. guillelmi. Meanwhile, the improvements of biomass of plants and animals also were consistent with the increasing of Cd concentration in both plants and earthworms after combined application. It showed that the Cd concentrations in P. vittata were the highest while the TFs of Cd in S. emarginatum displays significantly more than that in others. In conclusion, the recommended combined system of earthworm-plant (P. vittata-E. fetida P2 and P. vittata-P. guillelmi) to provide reference for soil Cd bioremediation system in practice.

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

Adsorption mechanism of Cd2+ on microbial inoculant and its potential for remediation Cd–polluted farmland soils

The adsorption characteristics and mechanism of Cd2+ on microbial inoculant (MI) mainly composed of Bacillus subtilis, Bacillus thuringiensis and Bacillus amyloliquefaciens, and its potential for remediation Cd polluted soils through batch adsorption and soil incubation experiments. It was found that the Freundlich isotherm model and the pseudo–second–order kinetics were more in line with the adsorption processes of Cd2+. The maximum adsorption capacity predicted by Langmuir isotherm model suggested that of MI was 57.38 mg g−1. Scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS) images exhibited the surface structure of MI was damaged to varying degrees after adsorption, and Cd element was distributed on the surface of MI through ion exchange. X–ray diffraction (XRD) results showed that CdCO3 was formed on the surface of MI. Moreover, the functional groups (–OH, C–H, and –NH) involved in the adsorption of Cd2+ through fourier transform infrared spectroscopy (FTIR). After applying MI to Cd–contaminated soil, it was found that soil pH, conductivity (EC) and soil organic matter (SOM) increased by 0.84 %–2.43 %, 31.6 %–241.48 %, and 8.11 %–24.1 %, respectively, when compared with the control treatments. The content of DTPA–Cd in the soils was significantly (P < 0.05) reduced by 15.48 %–29.68 % in contrast with CK, and the Cd speciation was transformed into a more stable residual fraction. The activities of urease, phosphatase and sucrose were increased by 3.5 %–45.18 %, 57.00 %–134.18 % and 52.51 %–70.52 %, respectively, compared with CK. Therefore, MI could be used as an ecofriendly and sustainable material for bioremediation of Cd–contaminated soils.

Surface expression of metallothionein enhances bioremediation in Escherichia coli

Cadmium contamination is prevalent, and microorganisms are commonly employed for bioremediation to treat cadmium contamination in water. Bacteria accumulated Cd primarily through the cell wall or by secreting polysaccharides and proteins. Metallothionein (MT) is a protein with high affinity for Cd found in a variety of organisms. In this study, the EGR_09832 gene from Echinococcus granulosus was fused with Lpp-OmpA in the outer membrane of Escherichia coli by constructing a recombinant plasmid pBSD-LEF encoding LPP-OmpA- EGR_09832-Flag fusion protein. Then we displayed the metallothionein EGR_09832 from Echinococcus granulosus on the surface of E. coli DH5α cells, as verified by flow cytometry. The result indicated that displaying MT on the cell membrane indeed enhanced the cadmium tolerance of E. coli from 60 mg/L to 160 mg/L. Furthermore, Cd adsorption ability was more than double compared to the wild E. coli. Fourier-transform infrared spectroscopy indicated the amide II band at 1533 cm−1 may be associated with the MT displayed on the cell membrane. This study suggested that the expressing Cd-binding short peptides such as MT onto the surface of bacterial cells can improve microbial bioremediation. It proposed a novel solution of Cd bioremediation.

Effective Bioremediation of Cd, Cr, and Pb in Tannery Effluent Using Aspergillus fumigatus and Aspergillus terreus: Synergistic Effects of Using the Two Strains Together

Effective Bioremediation of Cd, Cr, and Pb in Tannery Effluent Using Aspergillus fumigatus and Aspergillus terreus: Synergistic Effects of Using the Two Strains Together

Bio-inoculation with Serratia CP-13 enhances Cd detoxification via modulation of phytohormone, gas exchange attributes and nutrient acquisition in maize cultivars cultivated in Cd-stressed soil

Heavy metals contamination of soil is increasing rapidly due to prompt in urbanization and industrialization. Recently, cadmium (Cd) pollution has emerged as a severe menace to plant and human health, while the use of plant growth promoting rhizobacteria (PGPR) has appeared as an economical approach for bioremediation of Cd toxicity in crop plants. In this study, the effect of Serratia sp. CP-13 inoculation on two maize cultivars in pre-Cd (0, 5, 12, 18, 26, 30 µM) spiked soil was evaluated. The combined effect of soil Cd and CP-13 application was assessed through the analysis of seed germination, plant biomass, phytohormones, gas exchange attributes, antioxidant production, plant Cd, and nutrient uptake in two (Sahiwal-2002, MMRI-Yellow) maize cultivars. Our outcomes exposed that single treatment of Cd-spiked soil significantly downregulates seed germination, plant biomass, plant nutrients, photosynthetic pigments, indole acetic acid (IAA), total protein, proline, total soluble sugar (TSS), stomatal conductance, transpiration rate, net photosynthesis, and antioxidant production, together with upregulating malondialdehyde (MDA), relative membrane permeability (RMP), abscisic acid (ABA), and Cd uptake in maize cultivars. However, this response of the maize crop against Cd-spiked soil was found to be maximal in Sahiwal-2002 at 30 µM Cd. Furthermore, the inoculation of Cd-resistant CP-13 significantly upregulates the plant accumulation of biomass, seed germination, antioxidants, IAA, gas exchange attributes, photosynthetic pigments, plant physiology, and nutrient uptake and downregulates the MDA, RMP, ABA, and root/shoot Cd accretion in two cultivars of maize. Moreover, this CP-13 based upregulation of plant growth was found to be cultivar (Sahiwal-2002) and Cd treatment (30 µM) specific by controlling the accumulation of lipid peroxidation, phytohormone content, and Cd detoxification. Further, our results indicate that the CP-13 might be a promising and cost effective future biofertilizer for bioremediation of soil Cd.

Removal of cadmium and arsenic from water through biomineralization.

Due to anthropogenic activities, heavy metals such as cadmium (Cd) and arsenic (As) are one of the most toxic xenobiotics contaminating water, thus affecting human health and the environment. The objective of the present investigation was to study the effect of ureolytic bacteria Bacillus paramycoides-MSR1 for the bioremediation of Cd and As from contaminated water. The B. paramycoides showed high resistance to heavy metals, Cd and As, with minimum inhibitory concentration (MIC) of 12.84 μM and 48.54 μM, respectively. The urease activity and calcium carbonate (CaCO3) precipitation were evaluated in artificial wastewater with different concentrations of Cd (0, 10, 20, 30, 40, 50, and 60 μM) and As (0, 20, 40, 60, 80, and 100 μM). The maximum urease activity in Cd-contaminated artificial wastewater was observed after 96 hours, which showed a 76.1% decline in urease activity as the metal concentration increased from 0 to 60 μM. Similarly, 14.1% decline in urease activity was observed as the concentration of As was increased from 0 to 100 μM. The calcium carbonate precipitation at the minimum inhibitory concentration of Cd and As-contaminated artificial wastewater was 189 and 183 mg/100 ml, respectively. The percentage removal of metal from artificially contaminated wastewater with varied concentrations was analyzed using atomic absorption spectroscopy (AAS). After 168 hours of incubation, 93.13% removal of Cd and 94.25% removal of As were observed. Microstructural analysis proved the presence of calcium carbonate in the form of calcite, confirming removal of cadmium and arsenic by microbially induced calcium carbonate precipitation (MICCP) to be promising technique for water decontamination.

Biotrophic interactions between plant and endophytic bacteria in removal of PAHs and Cd from contaminated soils enhanced by graphene oxide

Graphene oxide (GO)-mediated phytoremediation is a novel strategy for abating polycyclic aromatic hydrocarbons (PAHs) from contaminated soils, but the underlying mechanism has not been fully investigated. In this study, Fire Phoenix plants were grown in soils contaminated by 105.00 mg kg−1 or 154.55 mg kg−1 PAHs, containing 15 mg kg−1 Cd and 0.0, 0.3, 0.4, or 0.5 g kg−1 GO, respectively. After 150 days of plant growth, PAH removal rates from low-PAHs/Cd and high-PAHs/Cd soils amended with 0.4 g kg−1 GO were 78.95% and 73.21%, respectively. GO particularly promoted the biodegradation of high-ring PAHs as the removal rate increased by 55.69% on day 120 of plant growth. Dioxygenase genes including nidA and pdoA2 directly degraded PAHs in GO-induced remediation. GO mediated both upstream and downstream degradation pathways of PAHs, during which the tricarboxylic acid cycle initially dominated the downstream pathway followed by carbohydrate and amino acid metabolisms. Soil Cd was also significantly reduced by GO-enhanced root absorption. This study for the first time elucidated the mechanisms underpinning the interaction of Fire Phoenix plants with microorganisms in remediation of soil PAHs and Cd and illustrated the viability of GO-mediated bioremediation of PAHs and Cd from co-contaminated soils.

Amaranthus Biochar-Based Microbial Cell Composites for Alleviation of Drought and Cadmium Stress: A Novel Bioremediation Approach.

Metal contamination coupled with aridity is a major challenge for remediation of abiotic stressed soils throughout the world. Both biochar and beneficial bacteria showed a significant effect in bioremediation; however, their conjugate study needs more exploration. Two rhizobacteria strains Serratia sp. FV34b and Pseudomonas sp. ASe42b isolated from multi-metal and drought stressed sites showed multiple plant-growth-promoting attributes (phosphate solubilization, indole-3-acetic acid, siderophore, and ammonia production). Both strains were able to tolerate a high concentration of Cd along with being resistant to drought (-0.05 to -0.73 MPa). The seldom studied biomass of Amaranthus caudatus L. was used for biochar preparation by pyrolyzing it at 470 °C for 160 min under limited oxygen and then using it for the preparation of biochar-based microbial cell composites (BMC)s. To check the efficiency of BMC under Cd stress (21 mg kg-1 soil) and drought, a pot-scale study was conducted using Brassica napus L. for 47 days. Both the BMC5 (Biochar + Serratia sp. FV43b) and BMC9 (Biochar + Pseudomonas sp. ASe42b) improved the seed germination, plant biometrical (shoot and root biomass, length of organs) and physiological (photosynthetic pigments, proline, malondialdehyde, and relative water content) parameters under drought (exerted until it reaches up to 50% of field capacity) and Cd-spiked soil. However, for most of them, no or few significant differences were observed for BMC9 before and after drought. Moreover, BMC9 maximized the Cd accumulation in root and meager transfer to shoot, making it a best bioformulation for sustainable bioremediation of Cd and drought stressed soils using rapeseed plant.

Cadmium-absorptive Bacillus vietnamensis 151–6 reduces the grain cadmium accumulation in rice (Oryza sativa L.): Potential for cadmium bioremediation

Microbial bioremediation of heavy metal-polluted soil is a promising technique for reducing heavy metal accumulation in crops. In a previous study, we isolated Bacillus vietnamensis strain 151–6 with a high cadmium (Cd) accumulation ability and low Cd resistance. However, the key gene responsible for the Cd absorption and bioremediation potential of this strain remains unclear. In this study, genes related to Cd absorption in B. vietnamensis 151–6 were overexpressed. A thiol-disulfide oxidoreductase gene (orf4108) and a cytochrome C biogenesis protein gene (orf4109) were found to play major roles in Cd absorption. In addition, the plant growth-promoting (PGP) traits of the strain were detected, which enabled phosphorus and potassium solubilization and indole-3-acetic acid (IAA) production. Bacillus vietnamensis 151–6 was used for the bioremediation of Cd-polluted paddy soil, and its effects on growth and Cd accumulation in rice were explored. The strain increased the panicle number (114.82%) and decreased the Cd content in rice rachises (23.87%) and grains (52.05%) under Cd stress, compared with non-inoculated rice in pot experiments. For field trials, compared with the non-inoculated control, the Cd content of grains inoculated with B. vietnamensis 151–6 was effectively decreased in two cultivars (low Cd-accumulating cultivar: 24.77%; high Cd-accumulating cultivar: 48.85%) of late rice. Bacillus vietnamensis 151–6 encoded key genes that confer the ability to bind Cd and reduce Cd stress in rice. Thus, B. vietnamensis 151–6 exhibits great application potential for Cd bioremediation.

Phytoremediation of Heavy Metals from Irrigation Water, Faisalabad, Pakistan

A technique called phytoremediation makes use of a plant’s root system to draw contaminants, primarily heavy metals (zn, cr, and ni), from the surrounding rhizosphere. These are the end result of human actions such the use of pesticides, waste byproducts, cosmetics, and pharmaceuticals. This analysis focuses on soil contamination removal since prolonged exposure to heavy metals can cause respiratory illnesses, cardiovascular disorders, cancer of the liver, lungs, and kidneys, among other problems. In order to immobilise metals and change their harmful states into less toxic states, plants use a process called phytoremediation and tactics like phyto(rhizo) stabilisation. Chromium 6 is changed into chromium 3 through phytostabalization, a process in which plants are utilised to change a pollutant’s more hazardous form into a less hazardous volatile form that may be transported. Macrophytes, such as Arbidopsis thaliana and Cgara canescens, have been found to use phytofiltration and phytovolatization to remove radioactive and heavy metals. Indian mustard (Brassica juncea) and sun flower (Helianthus annus) are suitable plants for rhizofilteration, which is essential to prevent environmental and health problems. A heavy metal that is widely present in soil is cadmium. Cd can be removed physically in a number of ways, with membrane filtration and adsorption being the most often utilised techniques for doing so. Chemical (in which the addition of barium acetate caused coagulation) and biological (which uses microorganisms such bacteria, yeast species, fungal aspergillus, and green algea chlorel for the Bioremediation of Cd.) approaches are also employed for the removal of cadmium. In essence, phytoremediation uses the already-existing power of plant systems. This approach is more economical and environmentally benign than conventional approaches for cleaning up contaminated soil and ground water. Since drinking water contaminated with heavy metals is thought to be the primary cause of death in Pakistan, getting rid of these pollutants is our top priority.

A novel N-arachidonoyl-l-alanine-catabolizing strain of Serratia marcescens for the bioremediation of Cd and Cr co-contamination

Cadmium (Cd) and chromium (Cr) are widespread contaminants with a high risk to the environment and humans. Herein we isolated a novel strain of Serratia marcescens, namely strain S27, from soil co-contaminated with Cd and Cr. This strain showed strong resistance to Cd as well as Cr. S27 cells demonstrated Cd adsorption rate of 45.8% and Cr reduction capacity of 84.4% under optimal growth conditions (i.e., 30 °C, 200 rpm, and pH 7.5). Microscopic characterization of S27 cells revealed the importance of the functional groups C–O–C, C–H–O, C–C, C–H, and –OH, and also indicated that Cr reduction occurred on bacterial cell membrane. Cd(II) and Cr(VI) bioaccumulation on S27 cell surface was mainly in the form of Cd(OH)2 and Cr2O3, respectively. Further, metabolomic analyses revealed that N-arachidonoyl-l-alanine was the key metabolite that promoted Cd and Cr complexation by S27; it primarily promotes γ-linolenic acid (GLA) metabolism, producing siderophores and coordinating with organic acids to enhance metal bioavailability. To summarize, our results suggest that S27 is promising for the bioremediation of environments contaminated with Cd and Cr in tropical regions.

Evaluation of Haloferax mediterranei Strain R4 Capabilities for Cadmium Removal from Brines.

Haloferax mediterranei has revealed a high bioremediation potential for several inorganic anions (e.g., nitrates and nitrites) and metals from hypersaline waters and brines. However, it is unclear, to date, whether this microorganism allows Cd (II) bioremediation. Consequently, the main objective of this work was to assess the Cd (II) bioremediation potential of Hfx. mediterranei R4. To this end, Hfx. mediterranei cell growth rate and metal bioaccumulation were investigated using different culture media (complex, CM, and defined medium, DM) containing Cd (II) up to 1 mM. In addition, the elemental profile of the biomass (i.e., Al, Ba, Ca, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Sr and Zn) has also been monitored to gain insight into the metabolic processes that may be taking place at the intracellular level for Cd (II) removal. Because of the formation of CdS precipitate, CM is not a suitable culture media for evaluating Cd bioremediation since metal concentration could not be appropriately controlled. When operating in DM, it was observed that the cell doubling time increases three times in the presence of Cd (II). Hfx. mediterranei can bioaccumulate Cd, showing the highest significant accumulation at concentrations of 0.4 mM (108 ± 12 mg Cd/g dry tissue). Finally, the presence of Cd (II) affects the content of K, Mg, Mn and Zn in the biomass, by increasing K levels up to 27 ± 18% and Mn up to 310 ± 140% and reducing Mg levels up to 55 ± 36% and Zn up to 30 ± 4%. These results suggest that different mechanisms are involved in Cd (II) tolerance by Hfx. mediterranei, resulting in increasing the cell concentration of stress-tolerant elements in the biomass (K and Mn), while lowering the concentration of elements which Cd (II) competes with (Mg and Zn), and that all affects the physiological response of the organism by decreasing its growth rate.

Integrated analysis of transcriptomic and protein-protein interaction data reveals cadmium stress response in Geobacter sulfurreducens

Bacteria have evolved several mechanisms to resist Cd toxicity, which are crucial for Cd detoxication and have the potential to be used for bioremediation of Cd. Geobacter species are widely found in anaerobic environments and play important roles in natural biogeochemical cycles. However, the transcriptomic response of Geobacter sulfurreducens under Cd stress have not been fully elucidated. Through integrated analysis of transcriptomic and protein-protein interaction (PPI) data, we uncovered a global view of mRNA changes in Cd-induced cellular processes in this study. We identified 182 differentially expressed genes (|log2(fold change)| > 1, adjusted P < 0.05) in G. sulfurreducens exposed to 0.1 mM CdCl2 using RNA sequencing (RNA-seq). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that CdCl2 significantly affected sulfur compound metabolic processes. In addition, through PPI network analysis, hub genes related to molecular chaperones were identified to play important role in Cd stress response. We also identified a Cd-responsive transcriptional regulator ArsR2 (coded by GSU2149) and verified the function of ArsR2-ParsR2 regulatory circuit in Escherichia coli. This study provides new insight into Cd stress response in G. sulfurreducens, and identified a potential sensor element for Cd detection.

Efficient bioimmobilization of cadmium contamination in phosphate mining wastelands by the phosphate solubilizing fungus Penicillium oxalicum ZP6

In recent years, Cd contamination in phosphate mining wastelands has become increasingly serious, posing a great threat to ecological stability and human health. In this study, we aimed to investigate the bioremediation effect and mechanisms of phosphate-solubilizing fungi (Penicillium oxalicum ZP6) on Cd contamination in phosphate mining wastelands. A liquid shake-flask experiment showed that strain ZP6 was able to solubilize phosphate rock by reducing the pH, thus effectively removing Cd2+. Moreover, strain ZP6 adsorbed Cd2+ mainly through tight binding. Soil experiments showed that 81.64% Cd2+ removal was achieved after 21 d of inoculation with ZP6. FTIR and XRD analyses revealed that strain ZP6 achieved bioimmobilization of Cd2+ through the formation of Cd-phosphate and Cd-oxalate precipitates. Inoculation with strain ZP6 increased the microbial community diversity of Cd-contaminated soil from a phosphate mining wasteland, increasing the relative abundance of unclassified-d-unclassified and Actinobacteria. The activation of high-abundance genes (ATPF1A, atpD, GGT, cydA, and G6PD) was promoted, thereby enhancing the expression of signaling and metabolism-related functional genes. Our study indicates that strain ZP6 has enormous potential for bioremediation of Cd in phosphate mining wastelands. It also provides an efficient, green and economical biomaterial for remediating Cd contamination in phosphate mining wastelands.

Combined effects of Bacillus sp. M6 strain and Sedum alfredii on rhizosphere community and bioremediation of cadmium polluted soils.

Concerns regarding inevitable soil translocation and bioaccumulation of cadmium (Cd) in plants have been escalating in concomitance with the posed phytotoxicity and threat to human health. Exhibiting a Cd tolerance, Bacillus sp. M6 strain has been reported as a soil amendment owing to its capability of reducing metal bioavailability in soils. The present study investigated the rhizospheric bacterial community of the Cd hyperaccumulator Sedum alfredii using 16S rRNA gene sequencing. Additionally, the Cd removal efficiency of strain Bacillus sp. M6 was enhanced by supplementing with biochar (C), glutamic acid (G), and rhamnolipid (R) to promote the phytoremediation effect of hyperaccumulator S. alfredii. To the best of our knowledge, this is the first time the amendments such as C, G, and R together with the plant-microbe system S. alfredii-Bacillus sp. M6 has been used for Cd bioremediation. The results showed that soil CaCl2 and DTPA (Diethylenetriamine penta-acetic acid) extractable Cd increased by 52.77 and 95.08%, respectively, in all M6 treatments compared to unamended control (CK). Sedum alfredii with Bacillus sp. M6 supplemented with biochar and rhamnolipid displayed a higher phytoremediation effect, and the removal capability of soil Cd (II) reached up to 16.47%. Moreover, remediation of Cd polluted soil by Bacillus sp. M6 also had an impact on the soil microbiome, including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and cadmium transporting ATPase (cadA) genes. Quantitative PCR analysis confirmed the Bacillus sp. M6 strain increased the abundance of AOB and cadA in both low Cd (LC) and high Cd (HC) soils compared to AOA gene abundance. Besides, the abundance of Proteobacteria and Actinobacteria was found to be highest in both soils representing high tolerance capacity against Cd. While Firmicutes ranked third, indicating that the additionof strain could not make it the most dominant species. The results suggested the presence of the hyperaccumulator S. alfredii and Cd tolerant strain Bacillus sp. M6 supplemented with biochar, and rhamnolipid, play a unique and essential role in the remediation process and reducing the bioavailability of Cd.

Long-term bioremediation of cadmium contaminated sediment using sulfate reducing bacteria: Perspective on different depths of the sediment profile

Sulfate reducing bacteria (SRB) can be utilized for the in-situ remediation of heavy metal contaminated sediment, and the remediation processes occurring at different depths of the sediment profile are critical to the practical application of SRB. In this study, column reactors with sediment profile sampling devices were designed to investigate the variations in Cd speciation, labile S2− and microbial community at different depths of the sediment profile during the bioremediation of Cd contaminated sediment by SRB, over a 270 day monitoring period. In order to evaluate the remediation effect, in vitro extraction of sediment was performed with Sipunculus nudus intestinal juice to determine Cd bioavailability. Results showed that bioremediation caused acid soluble Cd to decrease in the surface sediment (0–6 cm), while reducible and residual fractions of Cd increased. The bioavailability of Cd in the surface sediment reduced by 25.1 % compared to before bioremediation, while no significant changes were observed in other sediment layers. These results indicate that the surface sediment was the main remediation range when SRB were initially added at the water–sediment interface. Furthermore, labile Cd and S2− in the surface sediment of the bioremediation column reactor exhibited a negative correlation (P < 0.1), while they were positively correlated in the sediment profile below 12 cm (P < 0.1) and throughout the whole control column reactor (P < 0.1). This demonstrates that the correlation between labile Cd and S2− could potentially be used as an indicator to reflect the remediation performance. Principal component analysis results revealed that the remediation effect was related to the different Cd fractions, labile S2− and microbial community in the sediment, among which Cd speciation was the most influential factor. Overall, this research provides comprehensive foundation for the practical application of SRB for sediment in-situ remediation.