Mercury-resistant bacteria from salt marsh of Tagus Estuary: the influence of plants presence and mercury contamination levels

Bioremediation by Cupriavidus metallidurans Strain MSR33 of Mercury-Polluted Agricultural Soil in a Rotary Drum Bioreactor and Its Effects on Nitrogen Cycle Microorganisms

Nitrogen cycle microorganisms are essential in agricultural soils and may be affected by mercury pollution. The aims of this study are to evaluate the bioremediation of mercury-polluted agricultural soil using Cupriavidus metallidurans MSR33 in a rotary drum bioreactor (RDB) and to characterize the effects of mercury pollution and bioremediation on nitrogen cycle microorganisms. An agricultural soil was contaminated with mercury (II) (20-30 ppm) and subjected to bioremediation using strain MSR33 in a custom-made RDB. The effects of mercury and bioremediation on nitrogen cycle microorganisms were studied by qPCR. Bioremediation in the RDB removed 82% mercury. MSR33 cell concentrations, thioglycolate, and mercury concentrations influence mercury removal. Mercury pollution strongly decreased nitrogen-fixing and nitrifying bacterial communities in agricultural soils. Notably, after soil bioremediation process nitrogen-fixing and nitrifying bacteria significantly increased. Diverse mercury-tolerant strains were isolated from the bioremediated soil. The isolates Glutamicibacter sp. SB1a, Brevundimonas sp. SB3b, and Ochrobactrum sp. SB4b possessed the merG gene associated with the plasmid pTP6, suggesting the horizontal transfer of this plasmid to native gram-positive and gram-negative bacteria. Bioremediation by strain MSR33 in an RDB is an attractive and innovative technology for the clean-up of mercury-polluted agricultural soils and the recovery of nitrogen cycle microbial communities.

Mercury detoxification by absorption, mercuric ion reductase, and exopolysaccharides: a comprehensive study

Mercury (Hg), the environmental toxicant, is present in the soil, water, and air as it is substantially distributed throughout the environment. Being extremely toxic even at low concentration, its remediation is utterly important. Therefore, it is necessary to detoxify the contaminant within the acceptable limits before threatening the environment. Although various conventional methods are being used, irrespective of high cost, it produces intermediate toxic by-product too. Biological methods are eco-friendly, clean, greener, and safer for the remediation of heavy metals corresponding to the conventional remediation due to their economic and high-tech constraints. Bioremediation is now being used for Hg (II) removal, which involves biosorption and bioaccumulation mechanisms or both, also mercuric ion reductase, exopolysaccharide play significant role in detoxification of mercury by acting a potential instrument for the remediation of heavy metals. In this review paper, we shed light on problems caused by mercury pollution, mercury cycle, and its global scenario and detoxification approaches by biological methods and result found in the literature.

Genomic Characterization of a Mercury Resistant Arthrobacter sp. H-02-3 Reveals the Presence of Heavy Metal and Antibiotic Resistance Determinants

Nuclear production and industrial activities led to widespread contamination of the Department of Energy (DOE) managed Savannah River Site (SRS), located in South Carolina, United States. The H-02 wetland system was constructed in 2007 for the treatment of industrial and storm water runoff from the SRS Tritium Facility. Albeit at low levels, mercury (Hg) has been detected in the soils of the H-02 wetland ecosystem. In anoxic sediments, Hg is typically methylated by anaerobic microbiota, forming the highly neurotoxic methylmercury (MeHg), which biomagnifies across food webs. However, in surficial oxic wetland soils, microbially mediated demethylation and/or volatilization processes can transform Hg²⁺ into the less toxic Hg⁰ form which is released into the atmosphere, thus circumventing MeHg formation. To obtain a deeper understanding on bacterial Hg volatilization, a robust Hg-resistant (HgR) bacteria, called as strain H-02-3 was isolated from the H-02 soils. A draft genome sequence of this strain was obtained at a coverage of 700×, which assembled in 44 contigs with an N50 of 171,569 bp. The genomic size of the strain H-02-3 was 4,708,612 bp with a total number of 4,240 genes; phylogenomic analysis revealed the strain as an Arthrobacter species. Comparative genomics revealed the presence of 1100 unique genes in strain H-02-3, representing 26.7% of the total genome; many identified previously as metal resistance genes (MRGs). Specific to Hg-cycling, the presence of mercuric ion reductase (merA), the organomercurial lyase (merB), and the mercuric resistance operon regulatory protein, were identified. By inference, it can be proposed that the organomercurial lyase facilitates the demethylation of MeHg into Hg²⁺ which is then reduced to Hg⁰ by MerA in strain H-02-3. Furthermore, gene prediction using resistome analysis of strain H-02-3 revealed the presence of several antibiotic resistance genes (ARGs), that statistically correlated with the presence of metal resistant genes (MRGs), suggesting co-occurrence patterns of MRGs and ARGs in the strain. Overall, this study delineates environmentally beneficial traits that likely facilitates survival of Arthrobacter sp. H-02-3 within the H-02 wetland soil. Finally, this study also highlights the largely ignored public health risk associated with the co-development of ARGs and MRGs in bacteria native to historically contaminated soils.

Risk assessment of methylmercury in pregnant women and newborns in the island of Madeira (Portugal) using exposure biomarkers and food-frequency questionnaires

Methylmercury (MeHg) is a contaminant present in fish which exerts a severe impact on health predominantly exhibiting neurotoxicity that might irreversibly affect fetal neurodevelopment. Fish consumption in Portugal is the third highest in the world, particularly high in regions with fishing tradition such as the Madeira Archipelago. Therefore, this study aimed at assessing the risk of exposure to MeHg in a population of pregnant women residing in Madeira. Blood samples from pregnant women (533) and umbilical cord (194) were collected from volunteer participants collected at primary health services in Madeira (Portugal) and analyzed for total mercury (HgT) level. A food-frequency questionnaire was used to estimate exposure and indices of risk while HgT in blood were correlated with estimated exposure. Analysis of HgT levels in blood indicated that 30% of pregnant women surpassed the maximum safe level of 10 µg/L recommended by the WHO, which was derived from the consumption of predatory fish, rich in MeHg. In addition, HgT levels in cord blood were 1.3 fold higher than in maternal blood, indicating the high risk of exposure to MeHg in this population. It is thus important to provide nutritional advice concerning fish consumption as a food choice in order to reduce fetal exposure and potential neurologic damage.

Gene Determinants for Mercury Bioremediation as Revealed by Draft Genome Sequence Analysis of Stenotrophomonas sp. Strain MA5

A soilborne Stenotrophomonas sp. strain (MA5) that is resistant to mercury was isolated. A draft genome sequence-based analysis revealed a suite of gene determinants to resist mercury and other heavy metals, multidrug efflux, stress response, and membrane transport, and these provide cues to a suite of mechanisms that underpin cellular survival in contaminated soil.

A soilborne Stenotrophomonas sp. strain (MA5) that is resistant to mercury was isolated. A draft genome sequence-based analysis revealed a suite of gene determinants to resist mercury and other heavy metals, multidrug efflux, stress response, and membrane transport, and these provide cues to a suite of mechanisms that underpin cellular survival in contaminated soil.

Isolation and characterization of mercury-resistant bacteria from wastewater sources in Egypt

An important mechanism for microbial resistance to mercury is its reduction into elemental mercury (facilitated by the merA gene). Thirty-eight microbial isolates from a variety of wastewater sources in Egypt were collected. Approximately 14 of the 38 isolates exhibited not only a high degree of tolerance to mercury (up to 160 ppm) but also a high degree of resistance to other tested heavy metals (Cu, Co, Ni, and Zn). From these 14, the 10 most resistant isolates were selected for further study and were found to include 9 Gram-negative and 1 Gram-positive bacterial strains. Multi-antibiotic-resistance profiles were detected for 6 out of the 10 selected isolates. All the tested Gram-negative isolates (n = 9) harbored a plasmid-encoded merA gene. The mercury removal effectiveness for the 10 selected isolates ranged between 50% and 99.9%, among which Stenotrophomonas maltophilia ADW10 recorded the highest rate (99.9%; at an initial mercury concentration of 20 ppm). To the best of our knowledge, this is the first study to (i) demonstrate the presence of a multimetal-resistant S. maltophilia bacterium with a high mercury tolerance capacity that would make it a suitable candidate for future bioremediation efforts in heavy-metal-polluted areas in Egypt and (ii) report Pseudomonas otitidis as one of the mercury-resistant bacteria.

Evidence of Mercury Methylation and Demethylation by the Estuarine Microbial Communities Obtained in Stable Hg Isotope Studies

Microbial activity is a critical factor controlling methylmercury formation in aquatic environments. Microbial communities were isolated from sediments of two highly mercury-polluted areas of the Tagus Estuary (Barreiro and Cala do Norte) and differentiated according to their dependence on oxygen into three groups: aerobic, anaerobic, and sulphate-reducing microbial communities. Their potential to methylate mercury and demethylate methylmercury was evaluated through incubation with isotope-enriched Hg species (¹⁹⁹HgCl and CH₃²⁰¹HgCl). The results showed that the isolated microbial communities are actively involved in methylation and demethylation processes. The production of CH₃¹⁹⁹Hg was positively correlated with sulphate-reducing microbial communities, methylating up to 0.07% of the added ¹⁹⁹Hg within 48 h of incubation. A high rate of CH₃²⁰¹Hg degradation was observed and >20% of CH₃²⁰¹Hg was transformed. Mercury removal of inorganic forms was also observed. The results prove the simultaneous occurrence of microbial methylation and demethylation processes and indicate that microorganisms are mainly responsible for methylmercury formation and accumulation in the polluted Tagus Estuary.

Citrus Epicarp-Derived Biochar Reduced Cd Uptake and Ameliorates Oxidative Stress in Young Abelmoschus esculentus (L.) Moench (okra) Under Low Cd Stress

Due to the important role of biochar (BC) in reducing metal-toxicity in plants, this study was aimed at assessing the potential of citrus epicarp-derived BC in ameliorating Cd toxicity in young Abelmoschus esculentus (okra) under low Cd toxicity. Okra was grown in soil amended with BC at four treatment levels for 49 days as follows: control (A), sole 1.4 mg Cd/kg-spiked soil (B), 1.4 mg Cd/kg-spiked soil + 1% BC (C) and 1.4 mg Cd/kg-spiked soil + 3% BC (D). The results showed a dose-dependent reduction in shoot accumulation of Cd due to the BC application. In addition, compared to control and sole Cd-amended soil, BC treatments (both at 1% and 3% w/w) decreased the oxidative stress, and enhanced activities of enzymatic and non-enzymatic antioxidants in the young okra. Generally, the application of BC to the soil was effective in ameliorating the Cd-induced oxidative stress in okra with limited shoot bioaccumulation of Cd.

Microbial Diversity of Mer Operon Genes and Their Potential Rules in Mercury Bioremediation and Resistance

Background:

Mercury is a toxic metal that is present in small amounts in the environment, but its level is rising steadily, due to different human activities, such as industrialization. It can reach humans through the food chain, amalgam fillings, and other sources, causing different neurological disorders, memory loss, vision impairment, and may even lead to death; making its detoxification an urgent task.

Methods:

Various physical and chemical mercury remediation techniques are available, which generally aim at: (i) reducing its mobility or solubility; (ii) causing its vaporization or condensation; (iii) its separation from contaminated soils. Biological remediation techniques, commonly known as bioremediation, are also another possible alternative, which is considered as cheaper than the conventional means and can be accomplished using either (i) organisms harboring themeroperon genes (merB,merA,merR,merP,merT,merD,merF,merC,merE,merHandmerG), or (ii) plants expressing metal-binding proteins. Recently, differentmerdeterminants have been genetically engineered into several organisms, including bacteria and plants, to aid in detoxification of both ionic and organic forms of mercury.

Results:

Bacteria that are resistant to mercury compounds have at least a mercuric reductase enzyme (MerA) that reduces Hg+2to volatile Hg0, a membrane-bound protein (MerT) for Hg+2uptake and an additional enzyme, MerB, that degrades organomercurials by protonolysis. Presence of bothmerA andmerB genes confer broad-spectrum mercury resistance. However,merA alone confers narrow spectrum inorganic mercury resistance.

Conclusion:

To conclude, this review discusses the importance of mercury-resistance genes in mercury bioremediation. Functional analysis ofmeroperon genes and the recent advances in genetic engineering techniques could provide the most environmental friendly, safe, effective and fantastic solution to overcome mercuric toxicity.

Optimization of microbial detoxification for an aquatic mercury-contaminated environment

Mercury (Hg) reduction performed by microorganisms is well recognized as a biological means for remediation of contaminated environment. Recently, studies demonstrated that Hg-resistant microorganisms of Tagus Estuary are involved in metal reduction processes. In the present study, aerobic microbial community isolated from a highly Hg-contaminated area of Tagus Estuary was used to determine the optimization of the reduction process in conditions such as the contaminated ecosystem. Factorial design methodology was employed to examine the influence of glucose, sulfate, iron, and chloride on Hg reduction. In the presence of several concentrations of these elements, microbial community reduced Hg in a range of 37-61% of the initial 0.1 mg/ml Hg²⁺ levels. The response prediction through central composite design showed that the increase of sulfate concentration led to an optimal response in Hg reduction by microbial community, while the rise in chloride levels markedly decreased metal reduction. Iron may exert antagonistic effects depending upon the media composition. These results are useful in understanding the persistence of Hg contamination in Tagus Estuary after inactivation of critical industrial units, as well as data might also be beneficial for development of new bioremediation strategies either in Tagus Estuary and/or in other Hg-contaminated aquatic environments.

Evaluation of mercury methylation and methylmercury demethylation rates in vegetated and non-vegetated saltmarsh sediments from two Portuguese estuaries

Neurotoxic methylmercury (MMHg) is formed from inorganic divalent mercury (Hg²⁺). However, it is poorly understood to what extent different mercury (Hg) pools contribute to existent MMHg levels. In this study, ambient concentrations of total Hg (THg) and MMHg as well as rates of methylation and demethylation were measured simultaneously in sediments with and without salt-marsh plant vegetation, which were collected in Guadiana and Tagus estuaries, Portugal. Concurrent processes of Hg methylation and MMHg demethylation were directly monitored and compared by spiking sediments cores with stable isotope tracers of ¹⁹⁹Hg²⁺ and CH₃²⁰¹Hg⁺ followed by gas chromatographic separation and isotope-specific detection using inductively coupled plasma mass spectrometry. Compared to the Guadiana estuary, where concentrations were comparatively low, THg and MMHg levels varied between vegetated and non-vegetated sediments collected at the Rosário site (ROS) of the Tagus estuary. Methylation (K_M) and demethylation rates (K_D) were also different between estuaries being dependent on the presence of vegetation. In addition, the type of macrophyte species influenced K_M and K_D values. In fact, the highest K_M value was found in Sarcocornia fruticosa vegetated sediments at the Castro Marim site in Guadiana (CM, 0.160 day^-1) and the lowest K_M was observed in non-vegetated sediments at the Alcochete site in Tagus (ALC, 0.009 day^-1). K_D varied by a factor of three among sites with highest rates of demethylation observed in non-vegetated sediments in Guadiana (12 ± 1.3 day^-1, corresponding to a half-life of 1.4 ± 0.2 h). This study clearly shows that the presence of vegetation in sediments favors the formation of MMHg. Moreover, this effect might be site specific and further studies are needed to confirm the findings reported here.

Identification of Sesbania sesban (L.) Merr. as an Efficient and Well Adapted Phytoremediation Tool for Cd Polluted Soils

A pot experiment was carried out to assess Cd uptake and accumulation efficiency of Sesbania sesban. Plants were grown in soil spiked with 25, 50, 100, 150, 200, 250, and 300 mg/kg Cd. After 120 days, plants were harvested and analyzed for Cd content. A steady increase in Cd accumulation with increasing metal concentration in soil was observed for all treatments. Accumulation of Cd was greatest in roots (86.7 ± 6.3 mg/kg), followed by stem (18.59 ± 1.9 mg/kg), and leaf (3.16 ± 1.1 mg/kg). Chlorophyll content declined with increasing Cd concentration, while proline and protein content increased as compared to control. At higher Cd levels, root, shoot length, and biomass were all significantly reduced (p ≤ 0.001). An increase in total protein along with greater A₂₅₀/A₂₈₀ value suggested an increase in metal-protein complexes. Considering the rapid growth, high biomass, accumulation efficiency, and adaptive properties, this plant could be used as a valuable tool for the phytoremediation of Cd contaminated soils.

The effect of plant growth-promoting rhizobacteria on the growth, physiology, and Cd uptake of Arundo donax L

In this study, plant growth-promoting potential isolates from rhizosphere of 10 weed species grown in heavy metal-contaminated areas were identified and their effect on growth, antioxidant enzymes, and cadmium (Cd) uptake in Arundo donax L. was explored. Plant growth-promoting traits of isolates were also analyzed. These isolates were found to produce siderophores and enzymes such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and aid in solubilization of mineral nutrients and modulate plant growth and development. Based on the presence of multiple plant growth-promoting traits, isolates were selected for molecular characterization and inoculation studies. Altogether, 58 isolates were obtained and 20% of them were able to tolerate Cd up to 400 ppm. The sequence analysis of the 16S rRNA genes indicates that the isolates belong to the phylum Firmicutes. Bacillus sp. along with mycorrhizae inoculation significantly improves the growth, the activity of antioxidants enzymes, and the Cd uptake in A. donax than Bacillus alone. Highly significant correlations were observed between Cd uptake, enzymatic activities, and plant growth characteristics at 1% level of significance. The synergistic interaction effect between these organisms helps to alleviate Cd effects on soil. Heavy metal-tolerant isolate along with arbuscular mycorrhizae (AM) could be used to improve the phytoremedial potential of plants.

Toxicology of metals and metalloids: Promising issues for future studies in environmental health and toxicology

The function and behavior of chemical elements in ecosystems and in human health probably comprise one of the most studied issues and a theme of great interest and fascination in science. Hot topics are emerging on an annual basis in this field. Bearing this in mind, some promising themes to explore in the field of metals and metalloids in the environment and in toxicology are highlighted and briefly discussed herein.

Associations between omega-3 fatty acids, selenium content, and mercury levels in wild-harvested fish from the Dehcho Region, Northwest Territories, Canada

To better understand the risks and benefits of eating wild-harvested fish from the Northwest Territories, Canada, levels of total mercury (HgT) and selenium (Se) and composition of omega-3 fatty acid (n-3 FA) were measured in muscle tissue of fish harvested from lakes in the Dehcho Region, Northwest Territories, Canada. Average HgT levels ranged from 0.057 mg/kg (cisco) to 0.551 mg/kg (northern pike), while average n-3 FA concentrations ranged from 101 mg/100 g (burbot) to 1,689 mg/100 g (lake trout). In contrast to HgT and n-3 FA, mean Se concentrations were relatively similar among species. Consequently, species such as lake whitefish, cisco, and longnose sucker displayed the highest nutrient levels relative to HgT content. Levels of HgT tended to increase with fish size, while Se and n-3 FA levels were typically not associated with fork length or fish weight. Interestingly, HgT concentration was occasionally inversely related to tissue nutrient content. Significant negative correlations were observed between Hg and n-3 FA for lake trout, northern pike, and walleye. There were also significant negative correlations between Hg and Se noted for lake whitefish, cisco, and northern pike. Samples with the highest nutritional content displayed, on occasion, lower levels of HgT. This study provides valuable information for the design of probabilistic models capable of refining public health messaging related to minimizing Hg risks and maximizing nutrient levels in wild-harvested fish in the Canadian subarctic.

Characterization of cadmium-resistant bacteria for its potential in promoting plant growth and cadmium accumulation in Sesbania bispinosa root

The cadmium (Cd) resistant bacteria were isolated from soils of Damanganga river, Vapi, and identified 11 potential Cd resistant bacteria based on 16S rDNA sequences. The Cd resistant bacteria belonged to four different genera: Providencia spp., Morganella sp., Stenotrophomonas sp., and Bacillus spp. The assessment of plant growth-promoting (PGP) parameters revealed that the Cd tolerant bacteria showed one or more PGP properties. Further, a pot experiment was conducted to elucidate the effects of Cd resistant bacteria on the plant growth and the uptake of Cd by Sesbania bispinosa. The bacterized seedlings recorded 36.0-74.8% and 21.2-32.9% higher root and shoot lengths, respectively, in Cd amended soil compared with control. The Cd mobilization in the root of S. bispinosa by microbial inoculants ranged from 0.02 ± 0.01 to 1.11 ± 0.06 ppm. The enhanced concentrations of Cd accumulation in S. bispinosa roots correspond to the effect of the bacterial strains on metal mobilization in soil. The present observations showed that the Cd resistant strains protect the plants against the inhibitory effects of Cd, probably due to the production of PGP properties. The present results provided a new insight into the phytoremediation of Cd contaminated soil.

Protective effects of niacin against methylmercury-induced genotoxicity and alterations in antioxidant status in rats

This study investigates the potential beneficial effects of niacin (NA; vitamin B3) supplementation in rats chronically exposed to methylmercury (MeHg). Animals were randomly assigned to one of 4 groups (n = 6): Group I, control, received distilled water by gavage; Group II, received MeHg (100 µg/kg/d) by gavage; Group III, received NA (50 mg/kg/d) in drinking water; Group IV, received MeHg (100 µg/kg/d) by gavage + NA (50 mg/kg/d) in drinking water. Biochemical parameters levels of glucose, triglycerides, total cholesterol and fractions, and enzyme activities aspartate transaminase (AST) and alanine transaminase (ALT) were determined. Further, oxidative stress markers activity of glutathione peroxidase (GPx) and catalase (CAT) activity, as well as levels of reduced glutathione (GSH), malondialdehyde (MDA), and nitric oxide, were examined, and the comet assay was performed, using blood/plasma. Hg levels were measured in blood, brain, and kidneys of animals. Our results demonstrated that NA reduced adverse effects produced by MeHg. The mechanism underlying these effects appears to be related to the intrinsic antioxidant potential of NA. Considering the beneficial effects attributed to NA following MeHg exposure and that fish are the main source of both NA and MeHg, future studies need to evaluate the potential counteractive effect of NA against the adverse consequences of MeHg exposure in fish-eating populations.

Aerobic Mercury-resistant bacteria alter Mercury speciation and retention in the Tagus Estuary (Portugal)

Aerobic mercury-resistant bacteria were isolated from the sediments of two highly mercury-polluted areas of the Tagus Estuary (Barreiro and Cala do Norte) and one natural reserve area (Alcochete) in order to test their capacity to transform mercury. Bacterial species were identified using 16S rRNA amplification and sequencing techniques and the results indicate the prevalence of Bacillus sp. Resistance patterns to mercurial compounds were established by the determination of minimal inhibitory concentrations. Representative Hg-resistant bacteria were further tested for transformation pathways (reduction, volatilization and methylation) in cultures containing mercury chloride. Bacterial Hg-methylation was carried out by Vibrio fluvialis, Bacillus megaterium and Serratia marcescens that transformed 2-8% of total mercury into methylmercury in 48h. In addition, most of the HgR bacterial isolates showed Hg(2+)-reduction andHg(0)-volatilization resulting 6-50% mercury loss from the culture media. In summary, the results obtained under controlled laboratory conditions indicate that aerobic Hg-resistant bacteria from the Tagus Estuary significantly affect both the methylation and reduction of mercury and may have a dual face by providing a pathway for pollution dispersion while forming methylmercury, which is highly toxic for living organisms.

Inoculation with Metal-Mobilizing Plant-Growth-Promoting Rhizobacterium Bacillus sp. SC2b and Its Role in Rhizoremediation

A plant growth-promoting bacterial (PGPB) strain SC2b was isolated from the rhizosphere of Sedum plumbizincicola grown in lead (Pb)/zinc (Zn) mine soils and characterized as Bacillus sp. based on (1) morphological and biochemical characteristics and (2) partial 16S ribosomal DNA sequencing analysis. Strain SC2b exhibited high levels of resistance to cadmium (Cd) (300 mg/L), Zn (730 mg/L), and Pb (1400 mg/L). This strain also showed various plant growth-promoting (PGP) features such as utilization of 1-aminocyclopropane-1-carboxylate, solubilization of phosphate, and production of indole-3-acetic acid and siderophore. The strain mobilized high concentration of heavy metals from soils and exhibited different biosorption capacity toward the tested metal ions. Strain SC2b was further assessed for PGP activity by phytagar assay with a model plant Brassica napus. Inoculation of SC2b increased the biomass and vigor index of B. napus. Considering such potential, a pot experiment was conducted to assess the effects of inoculating the metal-resistant PGPB SC2b on growth and uptake of Cd, Zn and Pb by S. plumbizincicola in metal-contaminated agricultural soils. Inoculation with SC2b elevated the shoot and root biomass and leaf chlorophyll content of S. plumbizincicola. Similarly, plants inoculated with SC2b demonstrated markedly higher Cd and Zn accumulation in the root and shoot system, indicating that SC2b enhanced Cd and Zn uptake by S. plumbizincicola through metal mobilization or plant-microbial mediated changes in chemical or biological soil properties. Data demonstrated that the PGPB Bacillus sp. SC2b might serve as a future biofertilizer and an effective metal mobilizing bioinoculant for rhizoremediation of metal polluted soils.