Mechanism of Cr(VI) removal by efficient Cr(VI)-resistant Bacillus mobilis CR3.

Cr(VI) is a hazardous environmental pollutant that poses significant risks to ecosystems and human health. We successfully isolated a novel strain of Bacillus mobilis, strain CR3, from Cr(VI)-contaminated soil. Strain CR3 showed 86.70% removal capacity at 200 mg/L Cr(VI), and a good Cr(VI) removal capacity at different pH, temperature, coexisting ions, and electron donor conditions. Different concentrations of Cr(VI) affected the activity of CR3 cells and the removal rate of Cr(VI), and approximately 3.46% of total Cr was immobilized at the end of the reaction. The combination of SEM-EDS and TEM-EDS analysis showed that Cr accumulated both on the cell surface and inside the cells after treatment with Cr(VI). XPS analysis showed that both Cr(III) and Cr(VI) were present on the cell surface, and FTIR results indicated that the presence of Cr on the cell surface was mainly related to functional groups, such as O-H, phosphate, and -COOH. The removal of Cr(VI) was mainly achieved through bioreduction, which primarily occurred outside the cell. Metabolomics analysis revealed the upregulation of five metabolites, including phenol and L-carnosine, was closely associated with Cr(VI) reduction, heavy metal chelation, and detoxification mechanisms. In addition, numerous metabolites were linked to cellular homeostasis exhibited differential expression. Cr(VI) exerted inhibitory effects on the division rate and influenced critical pathways, including energy metabolism, nucleotide metabolism, and amino acid synthesis and catabolism. These findings reveal the molecular mechanism of Cr(VI) removal by strain CR3 and provide valuable insights to guide the remediation of Cr(VI)-contaminated sites.

Exploring the mechanism of enhanced Cr(VI) removal by Lysinibacillus cavernae microcapsules loaded with synthetic nano-hydroxyapatite.

In this study, nano-scale hydroxyapatite (HAP) powder was successfully synthesized from waste eggshells and combined with Lysinibacillus cavernae CR-2 to form bio-microcapsules, which facilitated the enhanced removal of Cr(VI) from wastewater. The effects of various parameters, such as bio-microcapsule dosage, HAP dosage, and initial Cr(VI) concentration on Cr(VI) removal, were investigated. Under different treatment conditions, the Cr(VI) removal followed the order of LC@HAP (90.95%) > LC (78.15%) > Free-LC (75.61%) > HAP (6.56%) > NM (0.23%) at the Cr(VI) initial concentration of 50 mg L-1. Relative to other reaction systems, the LC@HAP treatment exhibited a considerable decrease in total Cr content in the solution, with removal rates surpassing 70%. Additionally, the bio-microcapsules maintained significant biological activity after reacting with Cr(VI). Further characterization using SEM, FTIR, XPS, and XRD revealed that the Cr(VI) removal mechanisms by bio-microcapsules primarily involved biological reduction and HAP adsorption. The adsorption of Cr(III) by HAP predominantly occurred through electrostatic interactions and surface complexation, accompanied by an ion exchange process between Cr(III) and Ca(II). Hence, bio-microcapsules, created by combining L. cavernae with HAP, represent a promising emerging material for the enhanced removal of Cr(VI) pollutants from wastewater.

Effect of amino acids on biomineralization of lead ions by Aspergillus niger.

This study investigates the biomineralization of lead ions by Aspergillus niger from aqueous environments, focusing on the dynamic effects of fungal metabolism and biological components. Three biomolecules (glutamate, methionine, and lysine) were used to induce lead oxalate mineralization under lead stress. Comparative experiments were conducted to analyze the growth characteristics and Pb (II) removal ability of A. niger, as well as the morphological and structural properties of the resulting lead oxalate minerals using inductively coupled plasma atomic emission spectroscopy, X-ray powder diffraction, and scanning electron microscopy-energy dispersive spectroscopy techniques. The findings reveal that A. niger plays a crucial role in controlling the mineralization process of Pb (II), with biomineralization experiments demonstrating the specific morphogenesis of lead oxalate over time. Additionally, the inclusion of the three biomolecules in the system indirectly influenced the rate of Pb (II) removal and mineral morphology. These results contribute to a better understanding of A. niger-mediated biomineralization process of lead oxalate and suggest its potential application in the removal of Pb (II) from aqueous environments, particularly in combination with amino acids for enhanced immobilization and mineral recovery. PRACTITIONER POINTS: Fungal activity and amino acids play a crucial role in shaping lead oxalate crystals during water treatment processes. Specific amino acids can effectively delay lead oxalate recrystallization, enhancing the stability and removal efficiency of the crystals. Biomineralization mediated by fungi offers a promising and eco-friendly approach for lead removal and recovery in wastewater treatment. Exploring the influence of organic additives and fungal metabolism on crystal growth provides valuable insights for developing efficient remediation strategies. Further research on the utilization of fungi and amino acids can help with innovative and sustainable wastewater treatment technologies.

Microbial remediation mechanisms and applications for lead-contaminated environments.

High concentrations of lead (Pb) in agricultural soil and wastewater represent a severe threat to the ecosystem and health of living organisms. Among available removal techniques, microbial remediation has attracted much attention due to its lower cost, higher efficiency, and less impact on the environment; hence, it is an effective alternative to conventional physical or chemical Pb-remediation technologies. In the present review, recent advances on the Pb-remediation mechanisms of bacteria, fungi and microalgae have been reported, as well as their detoxification pathways. Based on the previous researches, microorganisms have various remediation mechanisms to cope with Pb pollution, which are basically categorized into biosorption, bioprecipitation, biomineralization, and bioaccumulations. This paper summarizes microbial Pb-remediation mechanisms, factors affecting Pb removal, and examples of each case are described in detail. We emphatically discuss the mechanisms of microbial immobilization of Pb, which can resist toxicity by synthesizing nanoparticles to convert dissolved Pb(II) into less toxic forms. The tolerance mechanisms of microbes to Pb are discussed at the molecular level as well. Finally, we conclude the research challenges and development prospects regarding the microbial remediation of Pb-polluted environment. The current review provides insight of interaction between lead and microbes and their potential applications for Pb removal.

Hexavalent chromium reduction and bioremediation potential of Fusarium proliferatum S4 isolated from chromium-contaminated soil.

Microbial remediation, utilizing reduction of Cr(VI) to Cr(III), is considered a promising method for lowering toxic environmental chromium levels. In this study, a Cr(VI)-resistant fungal strain, Fusarium proliferatum S4 (F. proliferatum), was isolated from seriously chromium-polluted soil at Haibei Chemical Plant, China. This strain for treatment chromium-containing solution resulted in 100.00%, 93%, and 74% removal at initial concentrations of 10, 30, and 50 mg L-1 Cr(VI), respectively, after 12 days of treatment in a batch mode. Contributions of different cell fractions to Cr(VI) removal were explored. The Cr(VI) removal capacity of various cell components from strong to weak was as follows: cytoplasm, cell secretions, and cell debris. Observations obtained by scanning electron microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy revealed that not only the cell surfaces but also the intracellular contents were involved Cr through adsorption, reduction, or accumulation. Fourier transform infrared spectra indicated that a large number of functional groups (amino, carbonyl, carboxyl, and phosphate groups) participated in chromium binding on the cell surface. X-ray photoelectron spectroscopy confirmed the presence of Cr on the cell surface only as Cr(III). The results have important implications for an in-depth understanding of microbial chromate reduction by F. proliferatum. This study provides an insight into the microbial Cr(VI) bioreduction efficiency, and mechanisms in the chromium-contaminated environment.

Proteomics study on immobilization of Pb(II) by Penicillium polonicum.

Lead (Pb) is widely distributed in nature and has important industrial applications, while being highly toxic. In this study, the Pb(II) biosorption and immobilization behavior of Penicillium polonicum was investigated through surface morphology observation and multiple experimental analysis. In addition, the molecular mechanism of Pb(II) immobilization was further explored through proteomics. The analysis of the removal ability of P. polonicum to Pb(II) has found that P. polonicum could remove Pb(II) up to 95% (initial 4 mM Pb(II)) in 12 d. Scanning Electron Microscope (SEM) revealed a large amount of Pb(II) adsorbed on the cell wall. Raman and Energy Disperse Spectroscopy (EDS) revealed the formation of large amounts of PbC2O4 minerals extracellularly. Field Emission High-resolution Transmission Electron Microscopy (FE-TEM) found that [Pb5(PO4)3Cl] formed on the cell surface and inside the cells. The iTRAQ technique was used to analyze the characteristics of the changes of proteins during the action between Pb(II) and P. polonicum, which further revealed the mechanism of P. polonicum against Pb(II) and biomineralization. It was found that differential proteins in terms of redox, ion binding, metabolic process and ribosome synthesis were predominant in the GO analysis. Together with some of the characterization experiments above, the mechanisms mentioned above was well explained. The up-regulated expression of related proteins involved in respiratory metabolic pathways, antioxidant stress, and degradation of intracellular hazardous substances in the P. polonicum intracellularly such as succinate dehydrogenase, ATPase and cytochrome c oxidase, could explain the high tolerance of P. polonicum to Pb(II). The up regulation of OAH was responsible for extracellular PbC2O4 production. The up regulation of proteins such as TXN and GFA promoted Pb-glutathione (Pb-GSH) complex formation. This study explores the mechanism of Pb removal by fungi from the proteomic level, and provides new ideas and ways for Pb biogeochemical research.

Efficient immobilization behavior and mechanism investigation of Pb(II) by Aspergillus tubingensis.

OBJECTIVES: To understand the mechanism of Pb(II) immobilized by Pb(II)-tolerant microbes. RESULTS: Aspergillus tubingensis isolated from the lead-zine mine was investigated through surface morphology observation and multiple experimental analysis in order to elucidate the Pb(II) biosorption and immobilization behavior. The maximum Pb(II) uptake capacity of A. tubingensis was about 828.8 mg L-1. Fourier transform-infrared spectra and environmental scanning electron microscope indicated that a large number of functional groups (carboxyl, phosphoryl and sulfydryl, etc.) participated in Pb(II) binding on the cell surface. Raman and X-ray diffraction, field emission high-resolution transmission electron microscopy and X-ray absorption fine structure investigation revealed that the Pb(II) loaded on the surface of the fungus could be transformed into PbCO3 and PbS nanocrystals. Meanwhile, Pb(II) transported into the cell would be oxidized to form lead oxide minerals (Pb2O3.333) over time. CONCLUSIONS: This study has important implications for an in-depth understanding of Pb(II) removal by A. tubingensis and provides guidance for remediating lead-polluted environment using microorganisms.