Characterization of Cd2+ biosorption by Pseudomonas sp. strain 375, a novel biosorbent isolated from soil polluted with heavy metals in Southern China

The Cd resistant mechanism of Proteus mirabilis Ch8 through immobilizing and detoxifying

Cadmium (Cd) pollution is a serious global environmental problem, which requires a global concern and practical solutions. Microbial remediation has received widespread attention owing to advantages, such as environmental friendliness and soil amelioration. However, Cd toxicity also severely deteriorates the remediation performance of functional microorganisms. Analyzing the mechanism of bacterial resistance to Cd stress will be beneficial for the application of Cd remediation. In this study, the bacteria strain, up to 1400 mg/L Cd resistance, was employed and identified as Proteus mirabilis Ch8 (Ch8) through whole genome sequence analyses. The results indicated that the multiple pathways of immobilizing and detoxifying Cd maintained the growth of Ch8 under Cd stress, which also possessed high Cd extracellular adsorption. Firstly, the changes in surface morphology and functional groups of Ch8 cells were observed under different Cd conditions through SEM-EDS and FTIR analyses. Under 100 mg/L Cd, Ch8 cells exhibited aggregation and less flagella; the Cd biosorption of Ch8 was predominately by secreting exopolysaccharides (EPS) and no significant change of functional groups. Under 500 mg/L Cd, Ch8 were present irregular polymers on the cell surface, some cells with wrapping around; the Cd biosorption capacity exhibited outstanding effects (38.80 mg/g), which was mainly immobilizing Cd by secreting and interacting with EPS. Then, Ch8 also significantly enhanced the antioxidant enzyme activity and the antioxidant substance content under different Cd conditions. The activities of SOD and CAT, GSH content of Ch8 under 500 mg/L Cd were significantly increased by 245.47%, 179.52%, and 241.81%, compared to normal condition. Additionally, Ch8 significantly induced the expression of Acr A and Tol C (the resistance-nodulation-division (RND) efflux pump), and some antioxidant genes (SodB, SodC, and Tpx) to reduce Cd damage. In particular, the markedly higher expression levels of SodB under Cd stress. The mechanism of Ch8 lays a foundation for its application in solving soil remediation.

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.

Unveiling the performance of a novel alkalizing bacterium Enterobacter sp. LYX-2 in immobilization of available Cd

A novel alkalizing strain Enterobacter sp. LYX-2 that could resist 400 mg/L Cd was isolated from Cd-contaminated soil, which immobilized 96.05% Cd2+ from medium. Cd distribution analysis demonstrated that more than half of the Cd2+ was converted into extracellular precipitated Cd through mobilization of the alkali-producing mechanism by the strain LYX-2, achieving the high immobilization efficiency of Cd2+. Biosorption experiments revealed that strain LYX-2 had superior biosorption capacity of 48.28 mg/g for Cd. Pot experiments with Brassica rapa L. were performed with and without strain LYX-2. Compared to control, 15.92% bioavailable Cd was converted to non-bioavailable Cd and Cd content in aboveground vegetables was decreased by 37.10% with addition of strain LYX-2. Available Cd was mainly immobilized through extracellular precipitation, cell-surface biosorption and intracellular accumulation of strain LYX-2, which was investigated through Cd distribution, Scanning Electron Microscope and Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis. In addition, the application of strain LYX-2 significantly promoted the growth of vegetables about 2.4-fold. Above results indicated that highly Cd-resistant alkalizing strain LYX-2, as a novel microbial passivator, had excellent ability and reuse value to achieve the remediation of Cd-contaminated soil coupled with safe production of vegetables simultaneously.

Potential applications of extremophilic bacteria in the bioremediation of extreme environments contaminated with heavy metals

Protecting the environment from harmful pollutants has become increasingly difficult in recent decades. The presence of heavy metal (HM) pollution poses a serious environmental hazard that requires intricate attention on a worldwide scale. Even at low concentrations, HMs have the potential to induce deleterious health effects in both humans and other living organisms. Therefore, various strategies have been proposed to address this issue, with extremophiles being a promising solution. Bacteria that exhibit resistance to metals are preferred for applications involving metal removal due to their capacity for rapid multiplication and growth. Extremophiles are a special group of microorganisms that are capable of surviving under extreme conditions such as extreme temperatures, pH levels, and high salt concentrations where other organisms cannot. Due to their unique enzymes and adaptive capabilities, extremophiles are well suited as catalysts for environmental biotechnology applications, including the bioremediation of HMs through various strategies. The mechanisms of resistance to HMs by extremophilic bacteria encompass: (i) metal exclusion by permeability barrier; (ii) extracellular metal sequestration by protein/chelator binding; (iii) intracellular sequestration of the metal by protein/chelator binding; (iv) enzymatic detoxification of a metal to a less toxic form; (v) active transport of HMs; (vi) passive tolerance; (vii) reduced metal sensitivity of cellular targets to metal ions; and (viii) morphological change of cells. This review provides comprehensive information on extremophilic bacteria and their potential roles for bioremediation, particularly in environments contaminated with HMs, which pose a threat due to their stability and persistence. Genetic engineering of extremophilic bacteria in stressed environments could help in the bioremediation of contaminated sites. Due to their unique characteristics, these organisms and their enzymes are expected to bridge the gap between biological and chemical industrial processes. However, the structure and biochemical properties of extremophilic bacteria, along with any possible long-term effects of their applications, need to be investigated further.

Characterization of bacterial diversity and capacity to remove lead of a consortium from mining soil

INTRODUCTION

At present, the presence of lead (Pb2+) continues to be a problem in water bodies due to its continuous use and high toxicity. The aim of this study was to investigate the bacterial diversity of a potential consortium used as a biosorbent for the removal of lead in an aqueous solution.

METHODS

The minimum inhibitory concentration and the mean lethal dose of the consortium were determined, and then the optimal variables of pH and temperature for the removal process were obtained. With the optimal conditions, the kinetic behavior was evaluated, and adjustments were made to different mathematical models. A Fourier transform infrared spectroscopy analysis was performed to determine the functional groups of the biomass participating in the removal process, and the diversity of the bacterial consortium was evaluated during Pb2+ removal by an Ion Torrent Personal Genome Machine System.

RESULTS

It was found that the intraparticle diffusion model was the one that described the adsorption kinetics showing a higher rate constant with a higher concentration of Pb2+, while the Langmuir model was that explained the isotherm at 35 °C, defining a maximum adsorption load for the consortium of 54 mg/g. In addition, it was found that Pb2+ modified the diversity and abundance of the bacterial consortium, detecting genera such as Pseudomonas, Enterobacter, Citrobacter, among others.

CONCLUSIONS

Thus, it can be concluded that the bacterial consortium from mining soil was a biosorbent with the ability to tolerate high concentrations of Pb2+ exposure. The population dynamics during adsorption showed enrichment of Proteobacteria phyla, with a wide range of bacterial families and genera capable of resisting and removing Pb2+ in solution.

Removal of toxic metal Cd (II) by Serratia bozhouensis CdIW2 using in moving bed biofilm reactor (MBBR)

The use of bioreactor technology to treat industrial wastewater containing heavy metals has created new perspectives. Cadmium metal is one of the toxic heavy metals that have harmful effects on human health and the environment. This research work presents a comprehensive approach for aqueous cadmium removal through biosorption in a moving bed biofilm reactor (MBBR). The bacterium resistant to Cd(II) (350 mg/L) CdIW2 was selected among 8 cadmium tolerant bacteria isolated from the industrial wastewater of the metal industry. 16S rRNA gene and phenotypic analysis showed that the bacterium CdIW2 is similar to Serratia bozhouensis. The highest biosorption capacity of 65.79 mg/g was acquired in optimal conditions (30 min, pH = 6, 0.5 g/L, and 35 °C). The biosorption of the CdIW2 strain was consistent with the Langmuir isotherm and the pseudo-second order kinetic and showed the process's spontaneous thermodynamic and endothermic results. The removal rate 91.74% of MBBR in batch mode was obtained in 72 h and 10 mg/L of Cd(II). Furthermore, continuous mode bioreactor analysis has shown high efficiency at intel loading rates of 6-36 mg/L. day for cadmium removal. The second order kinetic (Grau) was chosen as the suitable model for modeling the MBBR process. Although several studies have evaluated the removal of various types of heavy metals, none of the studies involved the use of a metal-resistant strain in an MBBR bioreactor.

Cadmium and lead removal by Mg/Fe bimetallic oxide-loaded sludge-derived biochar: batch adsorption, kinetics, and mechanism

Biochar is a valuable adsorbent for the removal of heavy metals from water, and it is important to explore ways to increase its heavy metal adsorption capacity. In this study, Mg/Fe bimetallic oxide was loaded onto sewage sludge-derived biochar to enhance its heavy metal adsorption capacity. Batch adsorption experiments for the removal of Pb(II) and Cd(II) were performed to evaluate the removal efficiency of Mg/Fe layer bimetallic oxide-loaded sludge-derived biochar ((Mg/Fe)LDO-ASB). The physicochemical properties of (Mg/Fe)LDO-ASB and corresponding adsorption mechanisms were studied. The maximum adsorption capacities of (Mg/Fe)LDO-ASB for Pb(II) and Cd(II), which were calculated by isotherm model, were 408.31 and 270.41 mg/g, respectively. Adsorption kinetics and isotherms analysis showed that the dominant adsorption process of Pb(II) and Cd(II) uptake by (Mg/Fe)LDO-ASB was spontaneous chemisorption and heterogeneous multilayer adsorption, and film diffusion was the rate-limiting step. SEM-EDS, FTIR, XRD, and XPS analyses revealed that the Pb and Cd adsorption processes of (Mg/Fe)LDO-ASB involved oxygen-containing functional group complexation, mineral precipitation, electron-π-metal interactions, and ion exchange. The order of their contribution was as follows: mineral precipitation (Pb: 87.92% and Cd: 79.91%) > ion exchange (Pb: 9.84% and Cd: 16.45%) > metal-π interaction (Pb: 0.85% and Cd: 0.73%) > oxygen-containing functional group complexation (Pb: 1.39% and Cd: 2.91%). Mineral precipitation was the main adsorption mechanism, and ion exchange played a crucial role in Pb and Cd adsorption.

Adsorption of Cd (II) by a novel living and non-living Cupriavidus necator GX_5: optimization, equilibrium and kinetic studies

Biosorbents have been extensively studied for heavy metal adsorption due to their advantages of low cost and high efficiency. In the study, the living and non-living biomass of Cupriavidus necator GX_5 previously isolated were evaluated for their adsorption capacity and/or removal efficiency for Cd (II) through batch experiments, SEM and FT-IR investigations. The maximum removal efficiency rates for the live and dead biomass were 60.51% and 78.53%, respectively, at an optimum pH of 6, a dosage of 1 g/L and an initial Cd (II) concentration of 5 mg/L. The pseudo-second-order kinetic model was more suitable for fitting the experimental data, indicating that the rate-limiting step might be chemisorption. The Freundlich isotherm model fit better than the Langmuir isotherm model, implying that the adsorption process of both biosorbents was heterogeneous. FT-IR observation reflected that various functional groups were involved in Cd (II) adsorption: -OH, -NH, C=O, C-O and C-C groups for the living biomass and -OH, -NH, C-H, C = O, C-N and N-H groups for the dead biomass. Our results imply that non-living biosorbents have a higher capacity and stronger strength for absorbing Cd (II) than living biomass. Therefore, we suggest that dead GX_5 is a promising adsorbent and can be used in Cd (II)-contaminated environments.

Preparation of biomass-based hydrogels and their efficient heavy metal removal from aqueous solution

In this work, a porous tobacco straw-based polyacrylic acid hydrogel STS-PAA with high adsorption performance was prepared by polymerizing pretreated waste tobacco straw (TS) with acrylic acid/potassium acrylate by UV radiation initiation. The adsorption performance of metal ions was investigated. The effects of different temperatures (25°C, 35°C, and 45°C), adsorption times (1-420 min), pH values (2.0-6.0) and initial concentrations (0.25-4.0 mmol L^-1) of metal ions on the adsorption amount of heavy metal ions were investigated. The results showed that the hydrogel had a high removal rate of Pb²⁺, Cd²⁺ and Hg²⁺ in aqueous solution. The adsorption of Pb²⁺ was particularly effective. When C₀ = 4.0 mmol L^-1, pH = 6, the equilibrium adsorption amount of Pb²⁺, Cd²⁺ and Hg²⁺ reached 1.49 mmol g^-1, 1.02 mmol L^-1 and 0.94 mmol g^-1, respectively. The chemical structure and morphology of the hydrogels were characterized by FT-IR, EDS, SEM and XPS. The Langmuir model fits well with the adsorption system. The kinetic data suggest the adsorption of Pb²⁺, Cd²⁺ and Hg²⁺ follow the pseudo-first-order model. This indicates that STS-PAA adsorption of three heavy metal ions is monolayer physical adsorption. Thermodynamic analysis shows that the adsorption of Pb²⁺, Cd²⁺ and Hg²⁺ by STS-PAA is an endothermic (ΔH>0) entropy increase (ΔS>0) non-spontaneous reaction.

Biosorption of heavy metals by microorganisms: Evaluation of different underlying mechanisms

Globally, ecotoxicologists, environmental biologists, biochemists, pathologists, and other experts are concerned about environmental contamination. Numerous pollutants, such as harmful heavy metals and emerging hazardous chemicals, are pervasive sources of water pollution. Water pollution and sustainable development have several eradication strategies proposed and used. Biosorption is a low-cost, easy-to-use, profitable, and efficient method of removing pollutants from water resources. Microorganisms are effective biosorbents, and their biosorption efficacy varies based on several aspects, such as ambient factors, sorbing materials, and metals to be removed. Microbial culture survival is also important. Biofilm agglomerates play an important function in metal uptake by extracellular polymeric molecules from water resources. This study investigates the occurrence of heavy metals, their removal by biosorption techniques, and the influence of variables such as those indicated above on biosorption performance. Ion exchange, complexation, precipitation, and physical adsorption are all components of biosorption. Between 20 and 35 °C is the optimal temperature range for biosorption efficiency from water resources. Utilizing living microorganisms that interact with the active functional groups found in the water contaminants might increase biosorption efficiency. This article discusses the negative impacts of microorganisms on living things and provides an outline of how they affect the elimination of heavy metals.

Existence of a novel heavy metal-tolerant Pseudomonas aeruginosa strain Zambia SZK-17 Kabwe 1: the potential bioremediation agent in the heavy metal-contaminated area

Bacterial biomass may serve as an important environmental cleaning agent to toxic heavy metal ions at the expense of chemical processes which are not environmentally friendly. This study aimed at characterizing bacterial agents which could serve as a potential in situ bioremediation agent at the site of isolation. The characterization was performed using both phenotypic and molecular approaches. A novel Pseudomonas aeruginosa strain Pseudomonas aeruginosa Zambia SZK17 Kabwe1 was successfully isolated, identified, and characterized. The strain showed a promising tolerance to heavy metals such as copper (2 mM), zinc, nickel (2 mM), cobalt (1 mM), and cadmium (0.5 mM) at the laboratory level. The bacterium has shown the bioaccumulation of at least 60% of copper (II) sulfate (0.3655 mg/l) with R = 69.75%, cadmium (II) chloride (0.0241 mg/l) with R = 69.98%, zinc (II) chloride (0.1389 mg/l) with R = 69.91%, nickel (II) chloride (0.1155 mg/l) with R = 69.92%, and cobalt (II) chloride (0.593 mg/l) with R = 69.92%. The highest bioaccumulation has been observed in heavy metals cadmium, zinc, nickel, and cobalt. Characterization of the bacterium on pH has revealed that at a very high pH (≥ 9) and lower (≤ 5.5) pH, the bacterium tended to have reduced growth with optimum growth at pH 8. The high temperature at around 40 °C had a negative effect on the growth performance of the bacterium while optimum growth was observed at 28 °C. This novel P. aeruginosa strain has shown the phenotypic attributes to become a potential bioremediation agent; however, further investigation needs to be done to understand the genes and or molecular mechanisms that drive their tolerance to multiple heavy metals.

Continuous Systems Bioremediation of Wastewaters Loaded with Heavy Metals Using Microorganisms

Heavy metal pollution is a serious concern of the modern era due to its widespread negative effects on human health and to the environment. Conventional technologies applied for the uptake of this category of persistent pollutants are complex, often expensive, and inefficient at low metal concentrations. In the last few years, non-conventional alternatives have been studied in search of better solutions in terms of costs and sustainability. Microbial adsorbents are one of the biomass-based sorbents that have extensively demonstrated excellent heavy metals removal capacity even at low concentrations. However, most of the carried-out research regarding their application in wastewater treatment has been performed in discontinuous systems. The use of microorganisms for the uptake of metal ions in continuous systems could be an important step for the upscale of the remediation processes since it facilitates a faster remediation of higher quantities of wastewaters loaded with heavy metals, in comparison with batch systems removal. Thus, the current research aims to analyze the available studies focusing on the removal of metal ions from wastewaters using microorganisms, in continuous systems, with a focus on obtained performances, optimized experimental conditions, and the sustainability of the bioremoval process. The present work found that microbial-based remediation processes have demonstrated very good performances in continuous systems. Further sustainability analyses are required in order to apply the bioremediation technology in an optimized environmentally friendly way in large-scale facilities.

Potentiality of phosphorus-accumulating organisms biomasses in biosorption of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions: Behaviors and mechanisms

Heavy metal pollution is consistently a critical global issue, and bioremediation is regarded as one of the most promising approaches. In this work, the biosorption characteristics of Cd(II), Pb(II), Cu(II) and Zn(II) from aqueous solutions using three phosphorus-accumulating organisms (PAOs) biomasses, Ochrobactrum cicero (PAB-006), Stenotrophomonas maltophilia (PAB-009), and Pseudomonas putida (PAB-0031), as biosorbents were investigated. Results indicated that the equilibrium biosorption capacities of biosorbents to heavy metal ions were sensitive to the solution pH, and increased with increasing pH values. The experimental data of Cd(II), Pb(II), Cu(II) and Zn(II) biosorption were in good agreement with the Pseudo-second-order, Redlich-Peterson and Temkin models, implying that the biosorption was a hybrid chemical reaction-biosorption process. In addition, the theoretical maximum biosorption capacities of Cd(II), Pb(II), Cu(II) and Zn(II) were calculated to be 67.84, 80.23, 50.56 and 63.07 mg/g for PAB-006, 59.99, 87.71, 39.26 and 64.00 mg/g for PAB-009 and 68.31, 85.43, 38.97 and 62.85 mg/g for PAB-031, respectively (pH = 5.0 ± 0.1, T = 25 °C), according to the parameters of the Langmuir model. Moreover, ionic strength had negligible influences or slight promoting effects, while humic acid exhibited positive effects on the removal of heavy metals. Further, PABs were stable and displayed excellent reusability. Characterization techniques of FTIR and XPS revealed that surface complexation, ion exchange, hydrogen bonding and electrostatic interaction were the main mechanisms involved in the biosorption process. In summary, the biosorbent PABs possessed high biosorption performance with excellent reusability, and which hold the great application prospect in the treatment of heavy metal contaminated water.

Cadmium tolerant microbial strains possess different mechanisms for cadmium biosorption and immobilization in rice seedlings

Heavy metal remediation, such as cadmium (Cd²⁺) by microbial strains is efficient and environment-friendly. In this current study, we exploited the potential of Bacillus strains (Cd²⁺-tolerant; NMTD17, GBSW22, and LLTC96) to regulate Cd²⁺ biosorption mechanisms and improve rice seedling growth. The results showed that initial concentration and contact time affected Cd²⁺ biosorption, and the kinetic models of pseudo orders were effective in the elaborate biosorption process. Mainly, the bacterial cell wall had the potential for Cd²⁺ biosorption, and we found non-significant biosorption alterations among bacterial strains' inner and outer surfaces of cell membranes. Furthermore, the Fourier transform infrared (FTIR) spectroscopy analysis identified the differences in functional groups, such as C-N, PO₂, -SO₃, CO, COOH, C-O, C-N, -OH, and -NH that interact in biosorption by Bacillus strains. The scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) examination revealed that the binding of Cd²⁺ to microbes was mostly based on ion exchange pathways. Moreover, the Bacillus strains responded to Cd²⁺ stress in rice under pot experiment at various concentrations (0, 0.25, and 0.50 mg kg^-1), and they also influenced the chlorophyll contents and antioxidants activities were studied. The analysis of physio-morphological parameters was observed to be increased, which indicated that all Bacillus strains showed significant effects on rice growth under Cd²⁺ stress. These results revealed that the selected strains had the capability for additional use in the development of Cd²⁺ bioremediation methods. These strains also provided plant growth-promoting (PGP) traits that can alleviate the harmful effects of Cd²⁺ in rice plants.

Remediation of heavy metal(loid) contaminated soil through green nanotechnology

Modern industrialization is progressively degrading soil quality due to heavy metal contamination. Heavy metal (HM) contamination of agricultural soil has gained considerable attention due to its rapidly increasing levels. Nanoparticles (NPs) have unique physicochemical properties that make them effective stress relievers. Material science has recently been emphasizing “green” synthesis as a reliable, environmentally friendly, and sustainable method of synthesizing different kinds of materials, such as alloys, metal oxides, hybrids, and bioinspired materials. Therefore, green synthesis can be viewed as an effective tool to reduce the detrimental effects of the traditional nanoparticle synthesis methods commonly used in laboratories and industries. The review briefly describes the biosynthesis of NPs, the use of nanobiotechnology to remediate heavy metal-contaminated soil, the effect that NPs have on growth and development of plants, the behavior of NPs within plants when exposed to pollutants and the mechanisms used to alleviate HM stress. In addition, a broad overview of the major types of nanomaterials used so far in bioremediation of toxic heavy materials, recent advances regarding HM stress and the possible mechanisms by which NPs and HM interact in the agricultural system are also discussed.

The removal of selenite and cadmium by immobilized biospheres: Efficiency, mechanisms and bacterial community

In this study, a complex bacterial consortium was enriched from a typical Pb-Zn mine area and immobilized by sodium alginate to form biospheres, which were used for treatment of selenite (Se(IV))- and cadmium (Cd(II))-containing wastewater without external carbon source. Batch experiments showed that the maximum Se(IV) removal efficiency was 92.36% under the optimal conditions of an initial pH of 5, dosage of 5 g/L, initial Se(IV) concentration of 7.9 mg/L and reaction time of 168 h. Subsequently, more than 99% of 11.2 mg/L Cd(II) was removed by the biospheres within 10 h. Physicochemical characterization showed that reduction and adsorption were the main mechanisms for Se(IV) and Cd(II) removal, respectively. During the removal process, selenium and CdSe nanoparticles were formed. Bacterial community analysis showed the dominant bacterial genera changed after treatment of Se(IV)- and Cd(II)-containing wastewater. Additionally, 16S rRNA gene function prediction results showed that amino acid transport, carbohydrate transport, ion transport and metabolism were the dominant gene functions. The present study provides a potential way for the biological treatment of Se(IV)- and Cd(II)-containing wastewater using immobilized biospheres without external carbon source in short-term.

Resistance properties and adaptation mechanism of cadmium in an enriched strain, Cupriavidus nantongensis X1T

Bacterial adaption to heavy metal stress is a complex and comprehensive process of multi-response regulation. However, the mechanism is largely unexplored. In this study, cadmium (Cd) resistance and adaptation mechanism in Cupriavidus nantongensis X1^T were investigated. Strain X1^T could resist the stress of 307 mg/L Cd²⁺ and remove 70% Cd²⁺ in 48 h. Spectroscopic analyses suggested interactions between Cd²⁺ with C-N, -COOH, and -NH ligands of extracellular polymeric substances. Whole-genome sequencing found that the resistance of Cd²⁺ in strain X1^T was caused by the joint action of Czc and Cad systems. Cd²⁺ at 20 mg/L elicited differential expression of 1157 genes in strain X1^T. In addition to the reported effects of uptake, adsorption, effluxion, and accumulation system, the oxidative stress system, Type-VI secretory protein system, Fe-S protein synthesis, and cysteine synthesis system in strain X1^T were involved in the Cd²⁺ resistance and accumulation. The intracellular accumulation content of Cd²⁺ in strain X1^T was higher than the extracellular adsorption content made strain X1^T to be an important resource strain in the bioremediation of Cd-contaminated sewage. The results provide a theoretical network for understanding the complex regulatory system of bacterial resistance and adaptation of Cd against stressful environments.

Adsorption Behavior of 3-phenoxybenzoic Acid by Lactobacillus Plantarum and Its Potential Application in Simulated Digestive Juices

3-PBA is a major degradation intermediate of pyrethroids. Its widespread existence in the environment poses a severe threat to the ecosystem and human health. This study evaluated the adsorption capacity of L. plantarum RS20 toward 3-PBA. Batch adsorption experiments indicated that the optimal adsorption conditions were a temperature of 37 °C and initial pH of 6.0–8.0, under which the removal rate was positively correlated with the cell concentration. In addition, there was no link between the incubation time and adsorption rate. The kinetic study showed that the adsorption process fitted well with the pseudo-second-order model, and the adsorption isotherms could be described by both Langmuir and Freundlich equations. Heat and acid treatments showed that the ability of strain RS20 in removing 3-PBA was independent of microbial vitality. Indeed, it was involved with chemisorption and physisorption via the cell walls. The cell walls made the highest contribution to 3-PBA removal, according to the adsorption experiments using different cellular components. This finding was further reconfirmed by SEM. FTIR spectroscopy analysis indicated that carboxyl, hydroxyl, amino groups, and –C–N were the functional sites for the binding of 3-PBA. The co-culture experiments showed that the adsorption of strain RS20 enhanced the degradation of 3-PBA by strain SC-1. Strain RS20 could also survive and effectively remove 3-PBA in simulated digestive juices. Collectively, strain RS20 could be employed as a biological detoxification agent for humans and animals by eliminating 3-PBA from foods, feeds, and the digestive tract in the future.

Effect of Environmental pH on Mineralization of Anaerobic Iron-Oxidizing Bacteria

Freshwater lakes are often polluted with various heavy metals in the Anthropocene. The iron-oxidizing microorganisms and their mineralized products can coprecipitate with many heavy metals, including Al, Zn, Cu, Cd, and Cr. As such, microbial iron oxidation can exert a profound impact on environmental remediation. The environmental pH is a key determinant regulating microbial growth and mineralization and then influences the structure of the final mineralized products of anaerobic iron-oxidizing bacteria. Freshwater lakes, in general, are neutral-pH environments. Understanding the effects of varying pH on the mineralization of iron-oxidizing bacteria under neutrophilic conditions could aid in finding out the optimal pH values that promote the coprecipitation of heavy metals. Here, two typical neutrophilic Fe(II)-oxidizing bacteria, the nitrate-reducing Acidovorax sp. strain BoFeN1 and the anoxygenic phototrophic Rhodobacter ferrooxidans strain SW2, were selected for studying how their growth and mineralization response to slight changes in circumneutral pH. By employing focused ion beam/scanning electron microscopy (FIB–SEM) and transmission electron microscopy (TEM), we examined the interplay between pH changes and anaerobic iron-oxidizing bacteria and observed that pH can significantly impact the microbial mineralization process and vice versa. Further, pH-dependent changes in the structure of mineralized products of bacterial iron oxidation were observed. Our study could provide mechanical insights into how to manipulate microbial iron oxidation for facilitating remediation of heavy metals in the environment.

Effective immobilization of heavy metals via reactive barrier by rhizosphere bacteria and their biofilms

As the portal of plants, rhizosphere microorganisms play an essential role in controlling the species, transformation, and bioavailability of heavy metals, yet the potential passivation mechanism is still unclear. In this study, two heavy metal resistant and growth-promoting rhizosphere bacteria were screened, and their mechanisms in dealing with external stress and immobilizing heavy metal were explored. The results showed that heavy metals inhibited the ability of Pseudomonas sp. H13 and Brevundomonas sp. H16 to promote plant growth, but stimulated the production of extracellular polysaccharides and inorganic labile sulfide, and enhanced biofilm formation, thereby significantly improved the removal efficiency of Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺. Compared with H16, the biofilm of H13 disintegrated rapidly in the later stage, so more metal ions were adsorbed on the planktonic cells. The C-OH and PO groups related to polysaccharides play a crucial role in heavy metal adsorption, and the immobilization mechanism of the planktonic cell is mainly ion exchange and group complex, but for H16, intracellular enrichment cannot be ignored. Functional group complexes played a dominant role in biofilm, and the immobilized heavy metals were more difficult to release into the environment. This study highlighted the potential application prospects of biofilm bacteria in heavy metal remediation and explained the reactive barrier of rhizosphere bacteria to heavy metals.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Transcriptome Analysis on Key Metabolic Pathways in Rhodotorula mucilaginosa Under Pb(II) Stress

Rhodotorula mucilaginosa shows adaption to a broad range of Pb²⁺ stress. In this study, three key pathways, i.e., glycolysis (EMP), the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (OXPHOS), were investigated under 0-2,500 mg · L^-1 Pb stress, primarily based on biochemical analysis and RNA sequencing. R. mucilaginosa cells showed similar metabolic response to low/medium (500/1000 mg · L^-1) Pb²⁺ stress. High (2,500 mg · L^-1) Pb²⁺ stress exerted severe cytotoxicity to R. mucilaginosa. The downregulation of HK under low-medium Pb²⁺ suggested a correlation with the low hexokinase enzymatic activity in vivo. However, IDH3, regulating a key step of circulation in TCA, was upregulated to promote ATP feedstock for downstream OXPHOS. Then, through activation of complex I & IV in the electron transport chain (ETC) and ATP synthase, ATP production was finally enhanced. This mechanism enabled fungal cells to compensate for ATP consumption under low-medium Pb²⁺ toxicity. Hence, R. mucilaginosa tolerance to such a broad range of Pb²⁺ concentrations can be attributed to energy adaption. In contrast, high Pb²⁺ stress caused ATP deficiency. Then, the subsequent degradation of intracellular defense systems further intensified Pb toxicity. This study correlated responses of EMP, TCA, and OXPHOS pathways in R. mucilaginosa under Pb stress, hence providing new insights into the fungal resistance to heavy metal stress. IMPORTANCE Glycolysis (EMP), the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (OXPHOS) are critical metabolism pathways for microorganisms to obtain energy during the resistance to heavy metal (HM) stress. However, these pathways at the genetic level have not been elucidated to evaluate their cytoprotective functions for Rhodotorula mucilaginosa under Pb stress. In this study, we investigated these three pathways based on biochemical analysis and RNA sequencing. Under low-medium (500-1,000 mg · L^-1) Pb²⁺ stress, ATP production was stimulated mainly due to the upregulation of genes associated with the TCA cycle and the electron transport chain (ETC). Such an energy compensatory mechanism could allow R. mucilaginosa acclimation to a broad range of Pb²⁺ concentrations (up to 1000 mg · L^-1). In contrast, high (2500 mg · L^-1) Pb²⁺ stress exerted its excessive toxicity by provoking ATP deficiency and damage to intracellular resistance systems. This study provided new insights into R. mucilaginosa resistance to HM stress from the perspective of metabolism.

Insights into the role of extracellular DNA in heavy metal adsorption

Extracellular polymeric substances (EPS) participate in heavy metal adsorption in the aquatic environments. Extracellular DNA (eDNA) is an essential component of EPS, but its involvement in metal binding remains ambiguous. Herein, the role of eDNA in Cd(II) and Ni(II) adsorption was described using a combination of semi-quantitative and qualitative approaches. EPS were extracted from Burkholderia sp. MBR-1 and eDNA accounted for 6.9% of the total mass of EPS. The eDNA in the extracted EPS was digested using the DNase II to prepare an eDNA-free EPS sample. Potentiometric titration unveiled that the number of total binding sites of the eDNA-free EPS was 19% lower than the untreated EPS. The Cd(II) and Ni(II) adsorption capacity of the eDNA-free EPS was lower than the untreated EPS at the pH range of 4-7. At pH 7, the results of batch adsorption experiments showed that removing eDNA from EPS resulted in declines of 12.6% and 15.7% in the adsorption capacities for Cd(II) and Ni(II), respectively. Furthermore, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy unraveled that the phosphoryl groups and purines of eDNA are responsible for Cd(II) and Ni(II) complexation. The results demonstrated that eDNA plays an essential role in heavy metal adsorption.

Bacterial strains found in the soils of a municipal solid waste dumping site facilitated phosphate solubilization along with cadmium remediation

Phosphate solubilizing bacteria (PSB) that can withstand high cadmium (Cd) stress is a desired combination for bioremediation. This study evaluated the Cd bioremediation potential of four PSB strains isolated from the contaminated soils of a municipal solid waste (MSW) discarding site (Guwahati, India). PSB strains were cultured in Pikovskaya (PVK) media, which led to higher acid phosphatase (ACP) activity and the release of organic acid. Optical density (OD) measurements were performed to determine the growth pattern of PSB; furthermore, Cd uptake by PSB was evaluated using infrared spectroscopy (IR) and X-Ray Diffraction (XRD) analyses. The 16S rRNA taxonomic analysis revealed that all the four promising PSB strains belonged to either Bacillus sp. or Enterobacter sp. One strain (SM_SS8) demonstrated higher tolerance towards Cd (up to 100 mg L^-1). Flow cytometry analysis revealed 70.92%, 46.93% and 20.4% viability of SM_SS8 in 10, 50 and 100 mg L^-1, respectively in PVK media containing Cd. This study has therefore substantiated the bioremediation of Cd from polluted soil by the PSB isolates. Thus, experimental results revealed a potential combo benefit, phosphate solubilization along with Cd remediation.

Analysis of the Genome of the Heavy Metal Resistant and Hydrocarbon-Degrading Rhizospheric Pseudomonas qingdaonensis ZCR6 Strain and Assessment of Its Plant-Growth-Promoting Traits

The Pseudomonas qingdaonensis ZCR6 strain, isolated from the rhizosphere of Zea mays growing in soil co-contaminated with hydrocarbons and heavy metals, was investigated for its plant growth promotion, hydrocarbon degradation, and heavy metal resistance. In vitro bioassays confirmed all of the abovementioned properties. ZCR6 was able to produce indole acetic acid (IAA), siderophores, and ammonia, solubilized Ca₃(PO₄)₂, and showed surface active properties and activity of cellulase and very high activity of 1-aminocyclopropane-1-carboxylic acid deaminase (297 nmol α-ketobutyrate mg⁻¹ h⁻¹). The strain degraded petroleum hydrocarbons (76.52% of the initial hydrocarbon content was degraded) and was resistant to Cd, Zn, and Cu (minimal inhibitory concentrations reached 5, 15, and 10 mM metal, respectively). The genome of the ZCR6 strain consisted of 5,507,067 bp, and a total of 5055 genes were annotated, of which 4943 were protein-coding sequences. Annotation revealed the presence of genes associated with nitrogen fixation, phosphate solubilization, sulfur metabolism, siderophore biosynthesis and uptake, synthesis of IAA, ethylene modulation, heavy metal resistance, exopolysaccharide biosynthesis, and organic compound degradation. Complete characteristics of the ZCR6 strain showed its potential multiway properties for enhancing the phytoremediation of co-contaminated soils. To our knowledge, this is the first analysis of the biotechnological potential of the species P. qingdaonensis.

Comparative Study of Heavy Metal Uptake and Analysis of Plant Growth Promotion Potential of Multiple Heavy Metal-Resistant Bacteria Isolated From Arable Land

Heavy metal-induced pollution is a serious environmental concern. This study was aimed at exploring indigenous heavy metal-resistant and plant growth promoting bacteria from arable land that might be useful for developing green strategies to counter the challenges related to bioremediation and sustainable agriculture. A thorough screening and characterization of all the twenty heavy metal-resistant bacterial isolates obtained in this study was done. Of these, three potent isolates were further analyzed to unravel their heavy metal resistance and uptake potentiality. Minimum inhibitory concentration determination depicted considerable tolerance (≥ 500 µg/mL) of the three isolates to Ni, Zn, Fe, Cd, Cu, etc. Growth kinetics of the isolates in presence of various heavy metals indicated differences between normal and metal-induced growth. pH tolerance and pigmentation ability of the isolates were also analyzed. Inductively Coupled Plasma-Mass Spectrometry study revealed maximum Cd uptake by the isolates during exponential phase of growth. One of the isolates demonstrated plant growth promotion ability detected using different in vitro qualitative screening tests. Molecular identification using 16S rRNA depicted the isolates as strains of Pseudomonas aeruginosa. This was the first study of heavy metal-resistant and plant growth promoting bacteria from this region. Further exploration of such multi metal-resistant indigenous bacteria may pave the way for designing effective strategies for bioremediation and sustainable agriculture.

Bioremediation potential of Pseudomonas genus isolates from residual water, capable of tolerating lead through mechanisms of exopolysaccharide production and biosorption

The mechanisms of tolerance to heavy metals used by some microorganisms identified by bioprospection processes are useful for the development and implementation of bioremediation strategies for contaminated environments with high toxic load caused by heavy metals. A total of seven native microbial isolates were obtained from wastewater bodies from an industrial zone in the municipality of Girardota, Antioquia, Colombia. Subsequently, they were selected to evaluate their lead tolerance capacity at different concentrations. In addition, some parameters were determined, such as the capacity to produce exopolysaccharides and their biosorption to understand potential mechanisms associated to lead tolerance. According to the biocehemical test (Vitek) and the molecular analysis of sequences of 16S rDNA, bacterial were identified as Pseudomonas aeruginosa, Pseudomonas nitroreducens, and Pseudomonas alcaligenes. We determined that the seven isolates had the capacity to tolerate concentrations higher than 50 mg/ml of lead, and that the concentration and exposure time (40 h) to this metal significantly affect the Pseudomonas spp. isolates. Statistically significant differences were detected (p < 0.05) in the production of the exopolysaccharide (EPS) among the isolates. P. aeruginosa (P16) was the strain with the maximum absorbance exopolysaccharide measured. We evidenced that P. aeruginosa (P14) and P. nitroreducens (P20) have 80% capacity to biosorber lead using live mass (minimum range from 80.9% to 87%). It is suggested that the tolerance to lead exhibited by the environmental isolates of Pseudomonas spp. can be attributed to the production of exopolysaccharides and biosorption, which are protection factors for its survival in contaminated places. Finally, it was determined that the adsorption measured from dead biomass was significant (p < 0.05) from 40 h of exposure to metal (Average 182.2 ± 7). We generated new knowledge about the potential use of the Pseudomonas spp. genus to bioremediate affluent contaminated with heavy metals.

Selenium improved the combined remediation efficiency of Pseudomonas aeruginosa and ryegrass on cadmium-nonylphenol co-contaminated soil

Most chemical plant wastewater contains both organic and inorganic pollutants, which are easy to diffuse along with surface runoff. The combined pollution of nonylphenol (NP) and cadmium (Cd) in soil is a serious problem that has not attracted enough attention. Based on the effects of selenium (Se) and Pseudomonas aeruginosa (P. aeruginosa) on plant and soil microbial communities, we speculated that the application of Se and P. aeruginosa in soil could improve the phytoremediation efficiency of ryegrass on contaminated soil. In this study, pot experiments with Cd and NP co-contaminated soil were conducted, and the results showed that application of P. aeruinosa alone could improve the removal rates of NP and Cd by ryegrass, and the supplementary of Se further enhanced the effect of micro-phyto remediation, with the highest removal rates of NP and Cd were 79.6% and 49.4%, respectively. The application of P. aeruginosa plus Se reduced the adsorption of Cd and NP through C-O and Si-O-Fe of the soil, changed the enzyme activity, and also affected the changing trend of the microbial community in soil. Pseudomonas, Sphingomonadales, Nitrospira, and other beneficial bacteria were enriched after a 60-day period with P. aeruginosa and Se treatment, thus promoting the removal of NP and Cd. In light of the above results, we suggest that P. aeruginosa application can efficiently facilitate the phytoremediation of ryegrass on Cd-NP co-contaminated soil, and Se supplementation in soil showed the synergistic effect on the remediation.

Biosorption of heavy metal ions by green alga Neochloris oleoabundans: Effects of metal ion properties and cell wall structure

Effects of metal ion proprieties and the cell wall structure of green alga Neochloris oleoabundans were investigated on five strategically selected heavy metal ions, Pb(II), Hg(II), Zn(II), Cd(II) and Cu(II). The biosorption of these ions were energy-independent and spontaneous Langmuir adsorption. The adsorption capacities of Pb(II), Hg(II), Zn(II), Cd(II) and Cu(II) were determined to be 1.03, 0.91, 1.20, 0.65 and 1.23 mmol/g, respectively. Data suggest that peptide-containing molecules and non-cellulosic polysaccharides on cell wall were the primary sites of adsorption. Ion Pb(II) showed the strongest inhibitive effects on the adsorption of other metal ions on cells in binaries, corresponding to its large affinity to the biosorbents, which was next only to that of Cu(II). A linear relation was established for the first time between the adsorption capacity and the impact factor, which is defined in this paper as the electronegativity of a metal ion normalized by its atomic radius. In other words, adsorption capacity of N. oleoabundans biomass to the tested two-valence metal ions is proportional to the electronegativity and inversely proportional to the radius of the metal ions. Cell aggregation was caused by the addition of Cu(II), which exhibited distinctive adsorption behaviors than other metal ions.

Assessment of resistance and biosorption ability of Lactobacillus paracasei to remove lead and cadmium from aqueous solution

Since heavy metals have been regarded as ubiquitous environmental pollutants, the exploitation of bacterial biosorption has been suggested as an applicable method for being employed for heavy metal depletion. The present study aimed to characterize the function of Lactobacillus paracasei in the presence of Pb (II) and Cd (II). The simultaneous effect of pH, initial metal concentration, and inoculum size demonstrated the Pb (II) removal of 85.77% at the lowest pH, while the inoculum size was enhanced to 45 CFU/100 ml. The maximum Cd (II) removal was obtained at a high level of pH and inoculum size, while the metal concentration was reduced to 30 ppb. The addition of Cd (II) concentration in access led to the 10% drop in Cd (II) removal efficiency attributed to the metal toxicity and pH. Additionally, the slight variation in the amount of inoculum size caused the decreasing trend in the Cd (II) removal. According to the obtained results, the benefit of L. paracasei in the biosorption of heavy metals was well-recognized, which could be suggested as an alternative candidate. PRACTITIONER POINTS: Strain of Lactobacillus paracasei as potential probiotics was tested for biosorption. A successful response surface method was proposed. L. paracasei showed a good efficiency for the lead and cadmium biosorption. Biosorption process was effective in removing low metal level from drinking water. The maximum biosorption was found to be 85.77% for Pb (II) obtained from the experiment.

The efficient biomineralization and adsorption of cadmium (Cd2+) using secretory organo-biominerals (SOBs) produced by screened Alcaligenes faecalis K2

Cadmium-contaminated wastewater has attracted increasing concerns due to its non-biodegradable properties and high toxicity. To explore eco-friendly and economically feasible strategies, the screened Alcaligenes faecalis K2 were employed for the biomineralization and recovery of Cd²⁺ from wastewater while producing considerable secretory organo-biominerals (SOBs) as bioadsorbents. At 75 mg/L Cd²⁺ exposure, 85.5% of Cd²⁺ was removed by K2, 43.0% of which was fixed in the granular SOBs. SOBs were convenient for separating from the solution. The adsorption capacity of granular sorbent made from SOBs was verified to be greater than 77.1 mg/g. Practically, 89.5% of 75 mg/L of Cd²⁺ could be stably removed while ereK2 continuously generated SOBs in a moving-bed biofilm reactor (MBBR). To sum up, the production of bioadsorbents can be achieved by K2, while removing Cd with live microorganisms, which was conducive to making full use of materials and improving Cd removal efficiency.

Effective removal of heavy metals from industrial effluent wastewater by a multi metal and drug resistant Pseudomonas aeruginosa strain RA-14 using integrated sequencing batch reactor

Sequencing batch reactor (SBR) is useful in removal of both non-biodegradable and biodegradable contaminants from wastewater. The main aim of the present investigation was to evaluate the potential of biocatalyst strain RA-14 on heavy metal removal under SBR. The selected strain was screened from the soil sediment contaminated with heavy metals. It was able to survive at different (Hg²⁺, Pb²⁺, Zn²⁺, Cu²⁺, Cd²⁺ and Ni²⁺) heavy metals (>500 ppm). The bacterial strain RA-14 showed maximum bioaccumulation potential than other strains. Heavy metal resistance patterns of Pb²⁺ > Cu² > Cd²⁺ > Hg²⁺, Ni²⁺ and Zn² was observed. Strain RA-14 was resistant to penicillin-G, nalidixic acid, ceftazidime, cefotaxime, kanamycin and ampicillin. The results revealed that bioaccumulation activities were improved at pH 7.0 (83.2 ± 1.8%), 40 °C (89.34 ± 3%) and affected at higher pH values and temperature. The results showed that contact time and initial Lead concentration was also affected Lead accumulation. The heavy metal tolerant strain RA-14 was further investigated towards heavy metal removal in SBR. Heavy metal was removed in SBR within 10 h of hydraulic retention time. Heavy metal removal was high at 2 mg/L (0.33 mg/L Cu²⁺, 0.33 mg/L Hg²⁺, 0.33 mg/L Pb²⁺, 0.33 mg/L Zn²⁺, 0.33 mg/L Cd²⁺ and 0.33 mg/L Ni²⁺) heavy metals. Total nitrogen, biological oxygen demand (BOD) and chemical oxygen demand (COD) of treated water in SBR was removed and the removal efficacy was 91.3 ± 2.1%, 97.6 ± 3.3%, and 94.3 ± 4.4%, respectively in 10 h hydraulic retention time. However, the efficiency of BOD, COD and total nitrogen content removal was decreased, due to the reduced metabolic process of bacteria after 10 h. The SBR reactor proved to be an efficient method for the treatment of various heavy metals from the wastewater.

A meta-analysis of metal biosorption by suspended bacteria from three phyla

Biosorption of heavy metals by bacterial biomass has been the subject of significant research interest in last decades due to its efficiency, relatively low cost and minimal negative effects for the surrounding environment. In this meta-analysis, the biosorption efficiencies of different bacterial strains for Cu(II), Cd(II), Zn(II), Cr(III), Mn(II), Pb(II) and Ni(II) were evaluated. Optimum conditions for the biosorption process such as initial metal concentration, temperature, pH, contact time, metal type, biomass dosage and bacterial phyla, were evaluated for each heavy metal. According to the results, the efficiencies of bacterial biomass for removal of heavy metal were as follows: Cd(II) > Cr(III) > Pb(II) > Zn(II) > Cu(II) > Ni(II) > Mn(II). Firmicute phyla showed the highest overall (living and dead) biosorption efficiency for heavy metals. Living biomass of Proteobacteria had the best biosorption performance. Living bacterial biomass was significantly more efficient in biosorption of Cu(II), Zn(II) and Pb(II) than dead biomass. The maximum biosorption efficiency of bacterial strains for Cd(II), Pb(II) and Zn(II) was achieved at pH values between 6 and 7.5. High temperatures (>35 °C) reduced the removal efficiencies for Cu(II) and Zn(II) and increased the efficiencies for Cd(II) and Cr(III) ions. The maximum biosorption efficiency of non-essential heavy metals occurred with short contact times (<2 h). Essential metals such as Zn and Cu were more efficiently removed with long biosorption durations (>24 h). The mean biosorption capacity of bacterial biomass was between 71.26 and 125.88 mg g^-1. No publication bias existed according to Egger's and Begg's test results.

Novel application of isolated Micrococcus luteus and Bacillus pumilus for Li+ ion biosorption: a comparative study

In this study, Li⁺ biosorption profiles of Micrococcus luteus and Bacillus pumilus bacterial strains were investigated. Comparative surface characterization of the biomasses revealed that B. pumilus had a significantly greater surface negativity than the other, which had a direct positive effect on the ability to attract the Li⁺ ions. Biosorption experiments showed that B. pumilus cell had more efficient performance at all pH and initial Li⁺ concentration values in the ranges of 3.0-10.0 and 2.5-20.0 mg/L, respectively. The maximum adsorption capacities obtained at initial Li⁺ concentration of 20.0 mg/L and pH 9.0 were 1.160 mg Li⁺/g (167.1 µmol/g) and 2.280 mg Li⁺/g (328.5 µmol/g) for M. luteus and B. pumilus, respectively. For all the cases studied, the biosorption equilibrium was reached very quickly, suggesting that physical interaction dominated this process. Experimental data were found to be compatible with both Langmuir and Freundlich models under the studied experimental conditions. This study highlights the idea that B. pumilus bacterial strain will be a new and preferred biosorbent for Li⁺ ions by providing a low cost, rapid and quite efficient process.

Performance and mechanisms for remediation of Cd(II) and As(III) co-contamination by magnetic biochar-microbe biochemical composite: Competition and synergy effects

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe₃O₄ biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g^-1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation.

Potentiality of living Bacillus pumilus SWU7-1 in biosorption of strontium radionuclide

Bacillus pumilus SWU7-1 was isolated from strontium ion (Sr(II))-uncontaminated soil, its biosorption potential was evaluated, and the effect of γ-ray radiation treatment on its biosorption was discussed. Domesticated under Sr(II) stress promoted the biosorption ability of B. pumilus to Sr(II), and the biosorption efficiency increased from 46.09% to 94.69%. At a lower initial concentration, the living bacteria had the ability to resist the biosorption of Sr(II). The optimal initial concentration range was 54-130 mg/L. The biosorption profile was better matched by Langmuir than Freundlich model, showing that the biosorption process of Sr(II) by the experimental strain was closer to the surface adsorption. According to Langmuir model, the maximum biosorption capacity of B. pumilus on Sr (II) was 299.4 mg/g. During the bacterial growth in the biosorption process, the changes in biosorption capacity and efficiency can be divided into two phases, and a pseudo-second-order model is followed in each phase. There was no significant difference in the biosorption efficiency of bacteria with different culture time after γ-ray radiation, and all of them were above 90%, which showed that B. pumilus had significant radiation resistance under experimental conditions. This study emphasized the potential application of B. pumilus in the treatment of radioactive Sr(II) pollution by biosorption.

Biosorption: A Review of the Latest Advances

Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.

Two plant growth promoting bacterial Bacillus strains possess different mechanisms in adsorption and resistance to cadmium

Microorganisms are promising biosorbents for decontaminating cadmium-polluted soil or water systems, but the underlying remediation mechanisms are still unclear. In this study, the cadmium biosorption mechanisms and capabilities of plant growth-promoting microorganisms (Bacillus megaterium NCT-2 and Bacillus paranthracis NT1) were investigated. Batch biosorption experiments showed that the optimal biosorption conditions for B. megaterium NCT-2 and B. paranthracis NT1 were pH 6.0, a biomass dosage of 1.0 g L^-1, and an initial Cd²⁺ concentration of 10 mg L^-1, and pH 8.0, a biomass dosage of 1.0 g L^-1, and an initial Cd²⁺ concentration of 10 mg L^-1, respectively. The biosorption processes of both biosorbents were well described by the pseudo-second order kinetic model, which indicated that the biosorption of Cd²⁺ was mainly chemisorption. The intracellular accumulation portion of adsorbed Cd²⁺ in B. megaterium NCT-2 was much higher than in B. paranthracis NT1 (43.11% and 3.25%, respectively), which resulted in the lower cadmium tolerance (14 mg L^-1 and 280 mg L^-1, respectively) and higher cadmium removal efficiency (46.79% and 20.45%, respectively) of B. megaterium NCT-2 compared to B. paranthracis NT1. SEM-EDS and FTIR analysis suggested the probable interactions of Cd²⁺ with the biosorbent surface ligands, such as -OH, -NH, -SO₃, CO and -COOH during surface adsorption. Results of qRT-PCR illustrated that the difference in cadmium resistant mechanism and adsorption performance between B. megaterium NCT-2 and B. paranthracis NT1 may be regulated by the genes cadA, zitB, khtT, and bshA and cadA, trkA, czcD, and bshA, respectively. Our results revealed that these two biosorbents have the potential for further use in the development of cadmium remediation technologies and could provide insight into the mechanisms of cadmium biosorption.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Screening strains for microbial biosorption technology of cadmium

Heavy metals contaminate the environment and provide a threat to public health through drinking water and food chain. Microbial biosorption technology provides a more economical and competitive solution for bioremediation of toxicants such as heavy metals, and microbial genetic modification may modify microbes towards optimal sorption. It is very important to screen suitable strains for this purpose. In this study, three different types of microorganisms Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae were isolated and identified, from uncontaminated soils, and compared their sorption differences with respect to cadmium (Cd²⁺). We evaluated the effects of contact time and initial concentration on Cd²⁺ uptake, and found pseudo-second-order kinetic models were more suitable to describe biosorption processes. Adsorption isotherms were used to reflect their biosorption capacity. The maximum biosorption capacities of three strains calculated by the Langmuir model were 37.764, 56.497, and 22.437 mg Cd/g biomass, respectively. In bacteria, Cd²⁺ biosorption mainly occurred on cell wall, while the difference in biosorption between yeast inside and outside the cell was not significant. We found that due to the structural differences, the removal rate of E. coli surface decreased at a high concentration, while S. cerevisiae still had a lower biosorption capacity. FTIR spectroscopy reflected the difference in functional groups involved in biosorption by three strains. SEM-EDS analysis showed the binding of Cd²⁺ to microorganisms mainly relied on ion exchange mechanism. Based on the above results, we suggested that B. subtilis is more suitable to get genetically modified for heavy metal biosorption.

Optimizing the Management of Cadmium Bioremediation Capacity of Metal-Resistant Pseudomonas sp. Strain Al-Dhabi-126 Isolated from the Industrial City of Saudi Arabian Environment

In this study, 23 bacterial strains were isolated from a Cadmium (Cd) contaminated soil in the industrial city, Riyadh of Saudi Arabia. Among these isolates six strains were found to withstand cadmium contamination and grow well. From the six isolates Pseudomonas sp. strain Al-Dhabi-122-127 were found to resist cadmium toxicity to a higher level. The isolates were subjected to biochemical and 16S rDNA gene sequence characterization to confirm their identification. The bacterial strain Al-Dhabi-124 showed 1.5 times higher Cd-degrading activity than Al-Dhabi-122 and Al-Dhabi-123, and Al-Dhabi-126 exhibited 3.5 times higher Cd-degrading activity, higher than the other strains. An atomic absorption spectrophotometer study showed that the strain Al-Dhabi-126 absorbed Cd, and that the bacterial strain Al-Dhabi-126 was found to tolerate cadmium level up to 2100 µg/mL. The bacterial strain Al-Dhabi-126 showed a maximum Cd removal efficacy at pH between 6.0 and 8.0. The efficacy decreased sharply after an increase in pH (9.0). An optimum temperature of 50 °C and pH 6.0 were found to be effective for the Cd removal process by the isolate. The study indicated that the bacterial strain Al-Dhabi-126 can be used effectively for the bioremediation of heavy metals like cadmium, a major toxic pollutant in industrial effluents.