Enhanced Biosorption of Nickel Ions on Immobilized Surface-Engineered Yeast Using Nickel-Binding Peptides

Spent brewer's yeast as a selective biosorbent for metal recovery from polymetallic waste streams

While the amount of electronic waste is increasing worldwide, the heterogeneity of electronic scrap makes the recycling very complicated. Hydrometallurgical methods are currently applied in e-waste recycling which tend to generate complex polymetallic solutions due to dissolution of all metal components. Although biosorption has previously been described as a viable option for metal recovery and removal from low-concentration or single-metal solutions, information about the application of selective metal biosorption from polymetallic solutions is missing. In this study, an environmentally friendly and selective biosorption approach, based on the pH-dependency of metal sorption processes is presented using spent brewer's yeast to efficiently recover metals like aluminum, copper, zinc and nickel out of polymetallic solutions. Therefore, a design of experiment (DoE) approach was used to identify the effects of pH, metal, and biomass concentration, and optimize the biosorption efficiency for each individual metal. After process optimization with single-metal solutions, biosorption experiments with lyophilized waste yeast biomass were performed with synthetic polymetallic solutions where over 50% of aluminum at pH 3.5, over 40% of copper at pH 5.0 and over 70% of zinc at pH 7.5 could be removed. Moreover, more than 50% of copper at pH 3.5 and over 90% of zinc at pH 7.5 were recovered from a real polymetallic waste stream after leaching of printed-circuit boards. The reusability of yeast biomass was confirmed in five consecutive biosorption steps with little loss in metal recovery abilities. This proves that spent brewer's yeast can be sustainably used to selectively recover metals from polymetallic waste streams different to previously reported studies.

Development of a Highly Selective Ni(II) Chelator in Aqueous Solution

The design, synthesis, and characterization of a novel Ni(II) chelator SG-20 is reported. SG-20 is selective in binding to Ni(II) versus other metal ions including Cu(II), Fe(II), Co(II), and Zn(II). At pH = 7.1, SG-20 binds Ni(II) with a Kd = 7.0 ± 0.4 μM. Job analysis indicates that SG-20 binds to both Ni(II) and Cu(II) with a 1:1 stoichiometry. Affinity of SG-20 for Ni(II) is pH dependent and decreases upon lowering to pH 4.0. A green solid was isolated from the reaction of SG-20 with NiCl2·6H2O in MeOH and characterized by X-ray photoelectron spectroscopy (XPS), electronic absorption and infrared (IR) spectroscopies, and mass spectrometry. Collectively, XPS and IR analysis revealed Ni-N and Ni-O interactions and a shift in C-O asymmetric and symmetric stretches consistent with Ni binding. Attempts to crystalize a mononuclear complex were unsuccessful, likely due to the Ni-SG-20 complex being in equilibrium with higher order species in solution. However, reaction of SG-20 with NiCl2·6H2O in water followed by slow evaporation yielded green crystals that were characterized by electronic absorption spectroscopy (λmax = 260 nm) and X-ray crystallography. These analyses revealed that SG-20 supports formation of a complex cluster containing six SG-20 ligands, 15 Ni(II), and three Na(I) centers, with two distinct types of Ni atoms in its outer and inner core. The nine Ni atoms present in the inner core were bound by oxo and carbonate bridges, whereas the six Ni atoms present in its outer shell were bound to N, O, and S donor atoms derived from SG-20. Overall, X-ray crystallographic analysis revealed that two chelator arms of SG-20 bind to one Ni(II) ion with an axial aqua ligand, whereas the third arm is free to interact with Ni ions within the central cluster, supporting the goal of Ni capture.

Characterization of the Binding Behavior of Specific Cobalt and Nickel Ion-Binding Peptides Identified by Phage Surface Display

In recent years, the application focus of phage surface display (PSD) technology has been extended to the identification of metal ion-selective peptides. In previous studies, two phage clones—a nickel-binding one with the peptide motif CNAKHHPRCGGG and a cobalt-binding one with the peptide motif CTQMLGQLCGGG—were isolated, and their binding ability to metal-loaded NTA agarose beads was investigated. Here, the free cyclic peptides are characterized by UV/VIS spectroscopy with respect to their binding capacity for the respective target ion and in crossover experiments for the other ion by isothermal titration calorimetry (ITC) in different buffer systems. This revealed differences in selectivity and affinity. The cobalt-specific peptide is very sensitive to different buffers; it has a 20-fold higher affinity for cobalt and nickel under suitable conditions. The nickel-specific peptide binds more moderately and robustly in different buffers but only selectively to nickel.

Insight Into the Molecular Mechanisms Underpinning the Mycoremediation of Multiple Metals by Proteomic Technique

We investigated the fungus Aspergillus fumigatus PD-18 responses when subjected to the multimetal combination (Total Cr, Cd2+, Cu2+, Ni2+, Pb2+, and Zn2+) in synthetic composite media. To understand how multimetal stress impacts fungal cells at the molecular level, the cellular response of A. fumigatus PD-18 to 30 mg/L multimetal stress (5 mg/L of each heavy metal) was determined by proteomics. The comparative fungal proteomics displayed the remarkable inherent intracellular and extracellular mechanism of metal resistance and tolerance potential of A. fumigatus PD-18. This study reported 2,238 proteins of which 434 proteins were exclusively expressed in multimetal extracts. The most predominant functional class expressed was for cellular processing and signaling. The type of proteins and the number of proteins that were upregulated due to various stress tolerance mechanisms were post-translational modification, protein turnover, and chaperones (42); translation, ribosomal structure, and biogenesis (60); and intracellular trafficking, secretion, and vesicular transport (18). In addition, free radical scavenging antioxidant proteins, such as superoxide dismutase, were upregulated upto 3.45-fold and transporter systems, such as protein transport (SEC31), upto 3.31-fold to combat the oxidative stress caused by the multiple metals. Also, protein–protein interaction network analysis revealed that cytochrome c oxidase and 60S ribosomal protein played key roles to detoxify the multimetal. To the best of our knowledge, this study of A. fumigatus PD-18 provides valuable insights toward the growing research in comprehending the metal microbe interactions in the presence of multimetal. This will facilitate in development of novel molecular markers for contaminant bioremediation.

Biosorption efficiency of nickel by various endophytic bacterial strains for removal of nickel from electroplating industry effluents: an operational study

Realising the hazardous effect of nickel on human health, microbes and plants are effectively used for bioremediation. The endophytic microorganisms have an important role in the phytoremediation of nickel using Vigna radiata. Therefore, in order to harness the potential of microbial strains, the present study was designed to examine the metal biosorption ability of endophytic bacterial strains isolated from plants growing in nickel-contaminated soil. A total of six endophytic nickel resistance bacteria were isolated from the plant Vigna radiata. The metal tolerant bacterial strains were identified following 16 S rRNA gene sequence analysis. Nickel biosorption estimation and plant growth-promoting (PGP) activities of isolated strains were performed and found high nickel biosorption efficiency of 91.3 ± 0.72% at 600 mg L^-1 using Bacillus safensis an isolated endophytic strain from Vigna radiata. Furthermore, high indole acetic acid (IAA) and exopolysaccharide (EPS) production were obtained in all the strains as compared to without nickel-containing medium used as control. Moreover, the production of high EPS suggests improved biosorption ability of isolated endophytic strains. In addition, a kinetic study was also performed to evaluate different adsorptions isotherms and support the nickel biosorption ability of endophytic strains. The treatment of nickel electroplating industrial effluent was also demonstrated by isolated endophytic strains. Among six (6) strains, B. cereus showed maximum 57.2 ± 0.62% biosorption efficiency of nickel which resulted in the removal of 1003.50 ± 0.90 mg L^-1 of nickel from the electroplating industry effluents containing initial 1791 ± 0.90 mg L^-1 of nickel. All other strains were also capable of significant nickel biosorption from electroplating industry effluents as well. Thus, isolated endophytic nickel tolerant strains can be further used at large-scale biosorption of nickel from electroplating industry effluent.

Transcription profiling-guided remodeling of sulfur metabolism in synthetic bacteria for efficiently capturing heavy metals

Heavy metal contamination is becoming a global problem threatening human health. Heavy metal removal by engineered microbes by cellular adsorption and uptake is a promising strategy for treatment of heavy metal contamination. However, this strategy is confronted with limited heavy metal-capturing elements. In this study, we performed a transcription profiling-guided strategy for construction of heavy metal-capturing synthetic bacteria. Transcription profiling of a heavy metal-tolerating Cupriavidus taiwanensis strain revealed up-regulation of sulfur metabolism-related operons (e.g., iscSAU and moaEDAB) by Pb²⁺ and Cd²⁺. A synthetic Escherichia coli strain, EcSSMO, was constructed by design of a synthetic sulfur metabolism operon (SSMO) based on iscSAU/moaEDAB. Biochemical analysis and X-ray photoelectron spectroscopy (XPS) revealed that the synthetic bacteria had remodeled sulfur metabolism and enhanced heavy metal-tolerating capacity, with higher surviving EcSSMO cells than the surviving control cells Ec0 (not containing SSMO) at 50 mg/L of Pb²⁺ and Cd²⁺ (>92 % versus <10 %). Moreover, EcSSMO exhibited much higher heavy metal-capturing capacity than Ec0, removing>90 % of Pb²⁺ and Cd²⁺ at 5 mg/L of Pb²⁺ and Cd²⁺, and >40 % of both heavy metals even at 50 mg/L of Pb²⁺ and Cd²⁺. This study reveals emphasizes feasibility of transcription profiling-guided construction of synthetic organisms by large-scale remodeling metabolic network.

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.