Yttrium immobilization through biomineralization with phosphate by the resistant strain Mesorhizobium qingshengii J19.

AIMS: Yttrium (Y) holds significant industrial and economic importance, being listed as a critical element on the European list of critical elements, thus emphasizing the high priority for its recovery. Bacterial strategies play a crucial role in the biorecovery of metals, offering a promising and environmentally friendly approach. Therefore, gaining a comprehensive understanding of the underlying mechanisms behind bacterial resistance, as well as the processes of bioaccumulation and biotransformation, is of paramount importance. METHODS AND RESULTS: A total of 207 Alphaproteobacteria strains from the University of Coimbra Bacteria Culture Collection were tested for Y-resistance. Among these, strain Mesorhizobium qingshengii J19 exhibited high resistance (up to 4 mM Y) and remarkable Y accumulation capacity, particularly in the cell membrane. Electron microscopy revealed Y-phosphate interactions, while X-ray diffraction identified Y(PO3)3·9H2O biocrystals produced by J19 cells. CONCLUSION: This study elucidates Y immobilization through biomineralization within phosphate biocrystals using M. qingshengii J19 cells.

Valorization of frying oil waste for biodetergent production using Serratia marcescens N2 and gamma irradiation assisted biorecovery.

BACKGROUND: The complexity, toxicity and abundance of frying oil waste (FOW) render it difficult to be degraded biologically. The aim of the present work was to valorize FOW and investigate the potential use of the produced biosurfactant by Serratia marcescens N2 (Whole Genome sequencing accession ID SPSG00000000) as a biodetergent. RESULTS: Serratia marcescens N2 demonstrated efficient valorization of FOW, using 1% peptone, 20% FOW and 8% inoculum size. Gene annotation showed the presence of serrawettin synthetase indicating that the produced biosurfactant was serrawettin. Zeta potential and Fourier Transform Infrared (FTIR) spectroscopy indicate that the biosurfactant produced was a negatively charged lipopeptide. The biosurfactant reduced the surface tension of water from 72 to 25.7 mN/m; its emulsification index was 90%. The valorization started after 1 h of incubation and reached a maximum of 83.3%. Gamma radiation was used to increase the biosurfactant yield from 9.4 to 19.2 g/L for non-irradiated and 1000 Gy irradiated cultures, respectively. It was noted that the biorecovery took place immediately as opposed to overnight storage required in conventional biosurfactant recovery. Both chemical and functional characteristics of the radiation induced biosurfactant did not change at low doses. The produced biosurfactant was used to wash oil stain; the highest detergency reached was 87% at 60 °C under stirring conditions for 500 Gy gamma assisted biorecovery. Skin irritation tests performed on experimental mice showed no inflammation. CONCLUSION: This study was able to obtain a skin friendly effective biodetergent from low worth FOW using Serratia marcescens N2 with 83% efficient valorization using only peptone in the growth media unlike previous studies using complex media. Gamma radiation was for the first time experimented to assist biosurfactant recovery and doubling the yield without affecting the efficiency.

Rapid and efficient reduction of chromate by novel Pd/Fe@biomass derived from Enterococcus faecalis.

Efficient reduction of chromate is highly desirable for its detoxification and remediation of the contaminated environment. This study described a fusion of the concepts of precious metal biorecovery and fabrication of Pd/Fe@biomass derived from simulated wastewater. The effectiveness of Pd/Fe@biomass during reduction process of Cr(VI) was evaluated by comparing with pure nZVI, E. faecalis and Pd@biomass. Results showed that Pd(II) could be recovered by E. faecalis with Fe(II) as the electron donor, and precipitation could yield nZVI anchored onto Pd-loaded E. faecalis. The nano particles (NPs) on Pd/Fe@biomass were well-dispersed, which provided 2.70 folds specific surface area comparing with nZVI. Efficient Cr(VI) reduction could be achieved at a higher catalyst dosage, the most appropriated Pd/Fe molar ratio of 2% and a wide pH range. Typically, 0.5 mM Cr(VI) could be completely reduced in 5 min driven by Pd/Fe@biomass under the conditions of dosage of 1.0 g/L and pH 3. Moreover, the mechanisms of Cr(VI) reduction by Pd/Fe@biomass were proposed, which intimately related to nZVI electron donating capacities, Pd catalysis for hydrogenation and galvanic cell effects between Fe and Pd. Therefore, Pd/Fe@biomass could be an alternative for rapid and complete reduction of Cr(VI).

Au(III)-induced extracellular electron transfer by Burkholderia contaminans ZCC for the bio-recovery of gold nanoparticles.

The biorecovery of gold (Au) by microbial reduction has received increasing attention, however, the biomolecules involved and the mechanisms by which they operate to produce Au nanoparticles have been not resolved. Here we report that Burkholderia contaminans ZCC is capable of reduction of Au(III) to Au nanoparticles on the cell surface. Exposure of B. contaminans ZCC to Au(III) led to significant changes in the functional group of cell proteins, with approximately 11.1% of the (C-C/C-H) bonds being converted to CO (8.1%) and C-OH (3.0%) bonds and 29.4% of the CO bonds being converted to (C-OH/C-O-C/P-O-C) bonds, respectively. In response to Au(III), B. contaminans ZCC also displayed the ability of extracellular electron transfer (EET) via membrane proteins and could produce reduced riboflavin as verified by electrochemical and liquid chromatography-mass spectrometric results, but did not do so without Au(III) being present. Addition of exogenous reduced riboflavin to the medium suggested that B. contaminans ZCC could utilize indirect EET via riboflavin to enhance the rate of reduction of Au(III). Transcriptional analysis of the riboflavin genes (ribBDEFH) supported the view of the importance of riboflavin in the reduction of Au(III) and its importance in the biorecovery of gold.

Non-Destructive Impedance Monitoring of Bacterial Metabolic Activity towards Continuous Lead Biorecovery.

The adverse health effects of the presence of lead in wastewater streams are well documented, with conventional methods of lead recovery and removal suffering from disadvantages such as high energy costs, the production of toxic sludge, and low lead selectivity. Klebsiella pneumoniae and Paraclostridium bifermentans have been identified as potential lead-precipitating species for use in a lead recovery bioreactor. Electrical impedance spectroscopy (EIS) on a low-cost device is used to determine the potential for the probe-free and label-free monitoring of cell growth in a bioreactor containing these bacteria. A complex polynomial is fit for several reactive equivalent circuit components. A direct correlation is found between the extracted supercapacitance and the plated colony-forming unit count during the exponential growth phase, and a qualitative correlation is found between all elements of the measured reactance outside the exponential growth phase. Strong evidence is found that Pb(II) ions act as an anaerobic respiration co-substrate for both cells observed, with changes in plated count qualitatively mirrored in the Pb(II) concentration. Guidance is given on the implementation of EIS devices for continuous impedance monitoring.

Tolerance of three fungal species to lithium and cobalt: Implications for bioleaching of spent rechargeable Li-ion batteries.

AIMS: This paper aims to quantify the growth and organic acid production of Aspergillus niger, Penicillium chrysogenum and Penicillium simplicissimum when these fungi are exposed to varying levels of lithium (Li) and cobalt (Co). The study also tests whether pre-exposing the fungi to these metals enables the fungi to develop tolerance to Li or Co. METHODS AND RESULTS: When cultures of A. niger, P. chrysogenum or P. simplicissimum were exposed to 250 mg l-1 of Li or Co, biomass production and excretion of organic acids were significantly inhibited after 5 days of growth compared to cultures grown in the absence of these metals. Pre-exposing cultures of A. niger to 250 mg l-1 of Li or Co for 20 days significantly increased biomass production when the fungus was subsequently sub-cultured into 250 or 500 mg l-1 of Li or Co. However, pre-exposure of P. chrysogenum or P. simplicissimum to 250 mg l-1 of Li or Co for 20 days did not increase biomass production. CONCLUSIONS: Aspergillus niger, but not the Penicillium species, developed tolerance to Li and to Co during the 20-day pre-exposure period. Therefore, processes that utilize fungal bioleaching with A. niger to mobilize and recover valuable metals such as Li or Co should consider a pre-exposure step for fungi to improve their tolerance to metal toxicity. SIGNIFICANCE AND IMPACT OF THE STUDY: Fungi may have the ability to extract valuable metals such as Li and Co from spent rechargeable batteries. However, the toxicity of the extracted metals can inhibit fungal growth and organic acid production. Pre-exposure to metals may alleviate toxicity for some fungal species. This knowledge can be used to improve the design of bioleaching protocols, increasing the potential for fungal bioleaching to become an economical and environmentally friendly method of recovering Li and Co from spent batteries.

Biorecovery of cobalt and nickel using biomass-free culture supernatants from Aspergillus niger.

In this research, the capabilities of culture supernatants generated by the oxalate-producing fungus Aspergillus niger for the bioprecipitation and biorecovery of cobalt and nickel were investigated, as was the influence of extracellular polymeric substances (EPS) on these processes. The removal of cobalt from solution was >90% for all tested Co concentrations: maximal nickel recovery was >80%. Energy-dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) confirmed the formation of cobalt and nickel oxalate. In a mixture of cobalt and nickel, cobalt oxalate appeared to predominate precipitation and was dependent on the mixture ratios of the two metals. The presence of EPS together with oxalate in solution decreased the recovery of nickel but did not influence the recovery of cobalt. Concentrations of extracellular protein showed a significant decrease after precipitation while no significant difference was found for extracellular polysaccharide concentrations before and after oxalate precipitation. These results showed that extracellular protein rather than extracellular polysaccharide played a more important role in influencing the biorecovery of metal oxalates from solution. Excitation-emission matrix (EEM) fluorescence spectroscopy showed that aromatic protein-like and hydrophobic acid-like substances from the EPS complexed with cobalt but did not for nickel. The humic acid-like substances from the EPS showed a higher affinity for cobalt than for nickel.

Efficient degradation of sodium diclofenac via heterogeneous Fenton reaction boosted by Pd/Fe@Fe3O4 nanoparticles derived from bio-recovered palladium.

Dehalogenation of emerging pollutants has attracted worldwide attention. In this study, novel bio-Pd/Fe@Fe3O4 nanoparticles (NPs) were proposed to boost the heterogeneous Fenton reaction for degradation of sodium diclofenac (DCF). Specifically, Enterococcus faecalis (E. faecalis) was employed to achieve bio-recovered palladium (bio-Pd). Results showed that expected preparation of bio-Pd/Fe@Fe3O4 NPs was confirmed by various characterization techniques. The prepared bio-Pd/Fe@Fe3O4 NPs were spherical morphology with average size of 9 nm. Under the optimum conditions, the removal efficiency of 10 mg/L DCF in 20 min and 40 min reached as high as 94.69% and 99.65%, respectively. The dechlorination and mineralization efficiencies of DCF were 85.16% and 59.21% in 120 min, respectively. The main degradation pathway of DCF was complete mineralization with the final products CO2, chloride ions and H2O. The improvement of dechlorination efficiency was ascribed to the accelerated corrosion of nano zero valent iron (nZVI) by Pd/Fe galvanic effect and the rise of active hydrogen. Meanwhile, more ferrous ions were released into this solution, resulting in the higher heterogeneous Fenton reaction rate driven by bio-Pd/Fe@Fe3O4 NPs. Therefore, the findings suggested that bio-Pd/Fe@Fe3O4 NPs were effective catalysts for DCF dechlorination and mineralization. The work provided a novel strategy for degradation of halogen-containing environmental pollutants.

Intensification of sorption-reduction coupled gold biorecovery process through microbial surface modification: effect on gold sorption and reduction.

Biorecovery is emerging as a promising approach to retrieve gold from various sources, while its efficiency is usually restricted by the limited functional groups on natural microbial biomass surface. This study aims to intensify Pycnoporus sanguineus boosted sorption-reduction coupled gold biorecovery process via microbial surface modification. Results showed that grafting polyallylamine hydrochloride onto P. sanguineus biomass surface increased amino group content on microbial biomass surface from 1.29 to 2.81 mmol/g. When applying modified biomass to gold biorecovery with initial gold concentrations of 1.0, 2.0 and 3.0 mM, biosorption equilibrium time shortened to the 12.5%, 37.5% and 41.7% of those obtained with pristine biomass, and sorption rate constants correspondingly increased to 11.2, 3.1 and 3.7 folds as well. Maximum sorption capacity increased 30% and the affinity between biomass and gold enhanced heavily after microbial surface modification. Meanwhile, microbial surface modification favored gold reduction and gold nanoparticles (AuNPs) formation. The change of microbial biomass morphology from smooth surface with some branched structure to layered stacking structure with many pores and the increase of amino group content on microbial biomass surface were the main impetus for the gold bioreocovery process intensification.

Microbe-mediated sustainable bio-recovery of gold from low-grade precious solid waste: A microbiological overview.

In an era of electronics, recovering the precious metal such as gold from ever increasing piles of electronic-wastes and metal-ion infested soil has become one of the prime concerns for researchers worldwide. Biological mining is an attractive, economical and non-hazardous to recover gold from the low-grade auriferous ore containing waste or soil. This review represents the recent major biological gold retrieval methods used to bio-mine gold. The biomining methods discussed in this review include, bioleaching, bio-oxidation, bio-precipitation, bio-flotation, bio-flocculation, bio-sorption, bio-reduction, bio-electrometallurgical technologies and bioaccumulation. The mechanism of gold biorecovery by microbes is explained in detail to explore its intracellular mechanistic, which help it withstand high concentrations of gold without causing any fatal consequences. Major challenges and future opportunities associated with each method and how they will dictate the fate of gold bio-metallurgy from metal wastes or metal infested soil bioremediation in the coming future are also discussed. With the help of concurrent advancements in high-throughput technologies, the gold bio-exploratory methods will speed up our ways to ensure maximum gold retrieval out of such low-grade ores containing sources, while keeping the gold mining clean and more sustainable.

Fungal formation of selenium and tellurium nanoparticles.

The fungi Aureobasidium pullulans, Mortierella humilis, Trichoderma harzianum and Phoma glomerata were used to investigate the formation of selenium- and tellurium-containing nanoparticles during growth on selenium- and tellurium-containing media. Most organisms were able to grow on both selenium- and tellurium-containing media at concentrations of 1 mM resulting in extensive precipitation of elemental selenium and tellurium on fungal surfaces as observed by the red and black colour changes. Red or black deposits were confirmed as elemental selenium and tellurium, respectively. Selenium oxide and tellurium oxide were also found after growth of Trichoderma harzianum with 1 mM selenite and tellurite as well as the formation of elemental selenium and tellurium. The hyphal matrix provided nucleation sites for metalloid deposition with extracellular protein and extracellular polymeric substances localizing the resultant Se or Te nanoparticles. These findings are relevant to remedial treatments for selenium and tellurium and to novel approaches for selenium and tellurium biorecovery.

Biotransformation of lanthanum by Aspergillus niger.

Lanthanum is an important rare earth element and has many applications in modern electronics and catalyst manufacturing. However, there exist several obstacles in the recovery and cycling of this element due to a low average grade in exploitable deposits and low recovery rates by energy-intensive extraction procedures. In this work, a novel method to transform and recover La has been proposed using the geoactive properties of Aspergillus niger. La-containing crystals were formed and collected after A. niger was grown on Czapek-Dox agar medium amended with LaCl3. Energy-dispersive X-ray analysis (EDXA) showed the crystals contained C, O, and La; scanning electron microscopy revealed that the crystals were of a tabular structure with terraced surfaces. X-ray diffraction identified the mineral phase of the sample as La2(C2O4)3·10H2O. Thermogravimetric analysis transformed the oxalate crystals into La2O3 with the kinetics of thermal decomposition corresponding well with theoretical calculations. Geochemical modelling further confirmed that the crystals were lanthanum decahydrate and identified optimal conditions for their precipitation. To quantify crystal production, biomass-free fungal culture supernatants were used to precipitate La. The results showed that the precipitated lanthanum decahydrate achieved optimal yields when the concentration of La was above 15 mM and that 100% La was removed from the system at 5 mM La. Our findings provide a new aspect in the biotransformation and biorecovery of rare earth elements from solution using biomass-free fungal culture systems.

Recovery of lanthanides from hydrocarbon cracking spent catalyst through chemical and biotechnological strategies.

The aim of this work is to evaluate the rare earth elements (REEs) recovery from fluid catalytic cracking spent catalyst (FCC-SC) by chemical and biochemical strategies while also examining a route for the valorization of biodiesel-derived glycerin (RG), which is presently unprofitable to refine. Recovery tests for REEs were performed with no pretreatment of the FCC-SC. A chemical leaching investigation was carried out using HCl, HNO3, NaOH, CaCl2 and citric acid aqueous solutions (1 mol L-1, at 30, 50, 60 or 70 ± 1 °C). The leaching tests carried out with 1 mol L-1 citric acid at 50 °C provided the best recovery of La (27%). Subsequent bioleaching tests were carried out with four strains of Yarrowia lipolytica to evaluate their potential to produce organic acids using RG as the main carbon source. The FCC-SC contains some REEs, predominantly La. Remarkable biorecovery rates for REEs (namely, La (53%), Ce and Nd (both 99%)) were achieved using the Y. lipolytica IM-UFRJ 50678 fermented medium at 50 °C. Thus, here, a sustainable approach to recovering metals from spent cracking catalyst using RG under low-cost and non-energy-intensive processing conditions is reported.

Elemental sulfur biorecovery from phosphogypsum using oxygen-membrane biofilm reactor: Bioreactor parameters optimization, metagenomic analysis and metabolic prediction of the biofilm activity.

This work investigated elemental sulfur (S0) biorecovery from Phosphogypsum (PG) using sulfur-oxidizing bacteria in an O2-based membrane biofilm reactor (MBfR). The system was first optimized using synthetic sulfide medium (SSM) as influent, then switched to biogenic sulfide medium (BSM) generated by biological reduction of PG alkaline leachate. The results using SSM had high sulfide-oxidation efficiency (98 %), sulfide to S0 conversion (∼90 %), and S0 production rate up to 2.7 g S0/(m2.d), when the O2/S ratio was ∼0.5 g O2/g S. With the BSM influent, the system maintained high sulfide-to-S0 conversion rate (97 %), and S0-production rate of 1.6 g S0/(m2.d). Metagenomic analysis revealed that Thauera was the dominant genus in SSM and BSM biofilms. Furthermore, influent composition affected the bacterial community structure and abundances of functional microbial sulfur genes, modifying the sulfur-transformation pathways in the biofilms. Overall, this work shows promise for O2-MBfR usage in S0 biorecovery from PG-leachate and other sulfidogenic effluents.

Gold Nanoparticles Bioproduced in Cyanobacteria in the Initial Phase Opened an Avenue for the Discovery of Corresponding Cerium Nanoparticles.

The production of isolated metallic nanoparticles with multifunctionalized properties, such as size and shape, is crucial for biomedical, photocatalytic, and energy storage or remediation applications. This study investigates the initial particle formations of gold nanoparticles (AuNPs) bioproduced in the cyanobacteria Anabaena sp. using high-resolution transmission electron microscopy images for digital image analysis. The developed method enabled the discovery of cerium nanoparticles (CeNPs), which were biosynthesized in the cyanobacteria Calothrix desertica. The particle size distributions for AuNPs and CeNPs were analyzed. After 10 h, the average equivalent circular diameter for AuNPs was 4.8 nm, while for CeNPs, it was approximately 5.2 nm after 25 h. The initial shape of AuNPs was sub-round to round, while the shape of CeNPs was more roundish due to their amorphous structure and formation restricted to heterocysts. The local PSDs indicate that the maturation of AuNPs begins in the middle of vegetative cells and near the cell membrane, compared to the other regions of the cell.

Evaluation and optimization of FTIR spectroscopy to quantify PHA production by municipal wastewater sludge.

Polyhydroxyalkanoate (PHA) is a family of naturally-occurring biopolymers synthesized by more than 300 microorganisms in the environment. These biopolymers have been investigated as a source material to substitute fossil fuel-based polymers; hence the synthesis of biopolymers and their characterization is a critical step in optimizing the process. Because of this, the biological production of PHA using PHA-producing microorganisms is currently the dominating process; however, the use of microbial mixed culture (MMC), such as wastewater sludge, is gaining attention. Different than pure cultures, MMC has higher culturing condition tolerance since the complex species composition and is easily obtained from wastewater treatment plants, which shortens the culturing time, lowers the cost, and promotes the application. The main constraint in MMC-based PHA is the extraction and quantification of PHA from the more complex matrix. In this paper, Fourier-transform infrared (FTIR) spectroscopy is evaluated to be used as a quantification method of PHA in MMC systems. Firstly, commercially available analytical standards, which consist of PHA/PHB, and two different solvents (chloroform and dichloromethane), were used and tested by this method, with KBr card and liquid cell methods, and the results are validated by gas chromatography mass spectrometry (GC/MS). The method was then tested using 12 samples from wastewater treatment plants. The PHA content in biomass varied from 3.42 w/w% to 1.22 w/w% following extraction with chloroform as solvent as determined by this method. In the four different combination standards, the best one is consisted of PHB and chloroform, and FTIR-liquid cell showed higher promise for PHA quantification in complex matrices.

Mediated biosynthesis of CdS QDs by EPS from Desulfovibrio desulfuricans sub sp. under carbon source-induced reinforcement.

This paper describes a unique molecular mechanism for the EPS-mediated synthesis of CdS QDs by sulfate-reducing bacteria (SRB) under carbon source-induced reinforcement. Under the induced by carbon sources (HCOONa, CH3COONa and C6H12O6), there was a significant increase in EPS production of SRB, particularly in protein, and the capacity of Cd(II) adsorption was further enhanced. CdS QDs were extracellularly synthesized by adding S2- after Cd(II) adsorption. The results showed that CdS QDs were wrapped or adhered by EPS, and the most significant increase in Arg and Lys among basic amino acids in EPS after HCOONa-induced was 133.34% and 63.89%, respectively. This may serve as a biological template for QD synthesis, producing protein gels with a large number of microcavities and controlling the nucleation of CdS QDs. The highest yield of HCOONa-CdS was achieved after induction, with 23.59 g/g biomass per unit strain, which was 447.34% higher than that before induction and was at a high level in previous studies. The synthesized CdS QDs were uniform in size distribution and had higher luminescence activity and a larger specific surface area than those synthesized by the chemical synthesis route, provides a new idea for EPS treatment of heavy metal wastewater and metal biorecovery.

Halo-alkaliphilic microbes as an effective tool for heavy metal pollution abatement and resource recovery: challenges and future prospects.

The current study presents an overview of heavy metals bioremediation from halo-alkaline conditions by using extremophilic microorganisms. Heavy metal remediation from the extreme environment with high pH and elevated salt concentration is a challenge as mesophilic microorganisms are unable to thrive under these polyextremophilic conditions. Thus, for effective bioremediation of extreme systems, specialized microbes (extremophiles) are projected as potential bioremediating agents, that not only thrive under such extreme conditions but are also capable of remediating heavy metals from these environments. The physiological versatility of extremophiles especially halophiles and alkaliphiles and their enzymes (extremozymes) could conveniently be harnessed to remediate and detoxify heavy metals from the high alkaline saline environment. Bibliometric analysis has shown that research in this direction has found pace in recent years and thus this review is a timely attempt to highlight the importance of halo-alkaliphiles for effective contaminant removal in extreme conditions. Also, this review systematically presents insights on adaptive measures utilized by extremophiles to cope with harsh environments and outlines the role of extremophilic microbes in industrial wastewater treatment and recovery of metals from waste with relevant examples. Further, the major challenges and way forward for the effective applicability of halo-alkaliphilic microbes in heavy metals bioremediation from extremophilic conditions are also highlighted.

Biointeraction of cerium oxide and neodymium oxide nanoparticles with pure culture Methylobacterium extorquens AM1.

Rare earth elements (REE) are valuable raw materials in our modern life. Extensive REE application from electronic devices to medical instruments and wind turbines, and non-uniform distribution of these resources around the world, make them strategically and economically important for countries. Current REE physical and chemical mining and recycling methods could have negative environmental consequences, and biologically-mediated techniques could be applied to overcome this issue. In this study, the bioextraction of cerium oxide and neodymium oxide nanoparticles (REE-NP) by a pure culture Methylobacterium extorquens AM1 (ATCC®14718™) was investigated in batch experiments. Results show that adding up to 1000 ppm CeO2 or Nd2O3 nanoparticles (REE-NP) did not seem to affect the bacterial growth over 14-days contact time. Effect of methylamine hydrochloride as an essential electron donor and carbon source for microbial oxidation and growth was also observed inasmuch as there was approximately no growth when it does not exist in the medium. Although very low concentrations of cerium and neodymium in the liquid phase were measured, concentrations of 45 µg/gcell Ce and 154 µg/gcell Nd could be extracted by M. extorquens AM1. Furthermore, SEM-EDS and STEM-EDS confirmed surface and intracellular accumulation of nanoparticles. These results confirmed the ability of M. extorquens to accumulate REE nanoparticles.

Electroactive Bacteria in Natural Ecosystems and Their Applications in Microbial Fuel Cells for Bioremediation: A Review.

Electroactive bacteria (EAB) are natural microorganisms (mainly Bacteria and Archaea) living in various habitats (e.g., water, soil, sediment), including extreme ones, which can interact electrically each other and/or with their extracellular environments. There has been an increased interest in recent years in EAB because they can generate an electrical current in microbial fuel cells (MFCs). MFCs rely on microorganisms able to oxidize organic matter and transfer electrons to an anode. The latter electrons flow, through an external circuit, to a cathode where they react with protons and oxygen. Any source of biodegradable organic matter can be used by EAB for power generation. The plasticity of electroactive bacteria in exploiting different carbon sources makes MFCs a green technology for renewable bioelectricity generation from wastewater rich in organic carbon. This paper reports the most recent applications of this promising technology for water, wastewater, soil, and sediment recovery. The performance of MFCs in terms of electrical measurements (e.g., electric power), the extracellular electron transfer mechanisms by EAB, and MFC studies aimed at heavy metal and organic contaminant bioremediationF are all described and discussed.