Immobilization Of Bacteria Research Articles

(Invited) Targeting Sustainability in Bioelectrochemical Systems for Water Quality Monitoring

Bioelectrochemical systems provide a sustainable approach to perform in-situ water quality monitoring, enabling the on-line detection of harmful contaminants in water samples. Specifically, interfacing intact microorganisms with abiotic electrodes allows developing bioelectrochemical systems for the early monitoring of several heavy metals and organic contaminants. Reports of microbial electrochemical sensors showed that a great number of contaminants can be monitored, achieving relevant sensitivity and stability.1 However, the sustainability of the utilized approaches, from biosensor setup to the choice of electrode materials, is not always considered, potentially limiting the applicability of the technology in the field.Here, focus is posed on the importance of targeting sustainability from the development to the application of microbial electrochemical sensors. Accordingly, a bio-inspired and bio-compatible approach for bacteria immobilization and redox mediation, as well as a bio-compatible route for electrode material development will be presented. Anoxygenic photosynthetic purple bacteria are utilized as the biophotocatalyst of choice, thanks to their extremely versatile metabolism where solar energy powers the oxidation of a broad variety of organic compounds. The use of these photosynthetic organisms is further motivated by their capability to cope and adapt to various environmental conditions (i.e., saline and non-saline environments, variable illumination conditions, presence of heavy metals)2, 3, making them of particular interest for applications in the field.4 Inspired by the natural approach utilized by mussels to obtain adhesive plaques, we explored an engineered deposition of polydopamine (PDA) for bacteria immobilization. The bio-inspired approach ensured firmly anchored purple bacteria on abiotic electrode surfaces while providing exogenous redox mediators to enhance photoexcited electrons harvesting. Focusing on the electrode material, we investigated the use of polyhydroxylkanoates (PHAs), biopolymers accumulated by a number of microorganisms, as biopolymer matrix to obtain homogeneous, flexible and free-standing electrodes. The coupling of these electrodes with photosynthetic bacteria for biophotoanodes development will be discussed, presenting advantages as well as future possibilities and challenges. References Chen, H.; Simoska, O.; Lim, K.; Grattieri, M.; Yuan, M.; Dong, F.; Lee, Y. S.; Beaver, K.; Weliwatte, S.; Gaffney, E. M.; Minteer, S. D. Chem. Rev. 2020, 120, 12903-12993.Giotta, L.; Agostiano, A.; Italiano, F.; Milano, F.; Trotta, M. Chemosphere 2006, 62, 1490-9.Gaffney, E. M.; Grattieri, M.; Beaver, K.; Pham, J.; McCartney, C.; Minteer, S. D. Electrochim. Acta 2020, 337, 135731.Grattieri, M. Photochem. Photobiol. Sci. 2020, 19, 424-435.

Porous floating Meretrix lusoria shell composite pellets immobilized with nitrate-reducing bacteria for treatment of phosphate and nitrate simultaneously from domestic wastewater

Removal of phosphate (PO43−) and nitrate (NO3−) from wastewater is essential to combat the major issue of eutrophication and other harmful associated threats. Hence, this study focused on designing feasibly applied adsorbents for efficient removal of PO43− and NO3−. A novel material, Porous Floating Meretrix lusoria Shell Composite (PFSC) pellet prepared from 75 to 85% soda lime silica, 6–16% dolomite and 4–14% M. lusoria F800 shell powder was able to float on water surface, which made it remarkable to apply, collect and reuse. PFSC pellets were found to effectively remove PO43−, and were used as the carriers for immobilization of various bacteria to develop Bacterial immobilized PFSC (Bac-immo-PFSC) pellets for NO3− removal from Domestic Wastewater (DWW). Highest NO3− removal was shown by immobilized PFSC pellets in the order of B. megaterium > P. aeruginosa > Pseudomonas sp. (Isolate 2) > Bacillus sp. (Isolate 4), respectively. Interestingly, the immobilization of PFSC pellets with mixed culture of B. megaterium and P. aeruginosa can remove 100% of NO3− alongwith removal of PO43−. Maximum adsorption capacity (Qmax) of PFSC pellets for PO43− and NO3− was 362 mg/g and 3.51 mg/g, respectively, whereas, among Bac-immo-PFSC pellets, Qmax of B. megaterium-immo-PFSC and P. aeruginosa-immo-PFSC pellets were 156 mgPO43−/g, 16.9 mgNO3−/g and 169 mgPO43−/g, 13.8 mgNO3−/g, respectively. This research identified higher expression of nitrous oxide reductase gene (nosZ) in case of B. megaterium, P. aeruginosa followed by Isolate 2 and Isolate 4, respectively. Hence, the application of novel PFSC and Bac-immo-PFSC pellets can be easily applied for effective PO43− and NO3− removal and thus, can be easily collected and reused for wastewater treatment.

Enhancement of carbofuran degradation by immobilized Bacillus sp. strain DT1

The widespread application of carbofuran has raised increasing concerns about health damage and environmental pollution. To degrade carbofuran in liquid and soil media, Bacillus sp. strain DT1 was isolated from soil. The isolated bacterial strain used the compound as a sole source of carbon and energy. Using rice straw as a material for bacteria immobilization resulting in 97.5% of the insecticide was degraded in a biofilm-batch reactor at the 3rd cycle, which was about 20% higher than using glass slides for immobilization. The chemical degradation in soils by bacteria immobilized in rice straw was also from 12.5% to 19.8% higher than by free counterparts. Furthermore, the dissipation rates in the previously-treated soils were higher than those in the untreated soils. Besides, the degradation of carbofuran by Bacillus sp. DT1 produced 3-hydroxycarbofuran, carbofuran 7-phenol and 2-hydroxy-3-(3-methypropan-2-ol) phenol as intermediate products. These findings demonstrated that Bacillus sp. DT1 immobilized in rice straw has a high potential for bioaugmentation of carbofuran in biofilm-batch reactor and in soils.

Simultaneous and sensitive determination of Escherichia coli O157:H7 and Salmonella Typhimurium using evanescent wave dual-color fluorescence aptasensor based on micro/nano size effect

The simultaneous and sensitive determination of two common pathogenic bacteria, Escherichia coli O157:H7 (E. coli O157:H7) and Salmonella Typhimurium (S. Typhimurium) was achieved using evanescent wave dual-color fluorescence aptasensor and the fiber nanoprobe through combining the micro/nano size and time-resolved effect. Two fluorescence labeled aptasensors, Cy3-apt-E and Cy5.5-apt-S, were regarded as biorecognition elements and signal reporters for E. coli O157:H7 and S. Typhimurium, which were alternatively excited by evanescent waves originated from 520 nm to 635 nm excitation lights, respectively. The fiber nanoprobe with in-situ etched nanopores was used for distinguishing free aptasensors and aptasensors bound to pathogenic bacteria based on the limited penetrated depth of evanescent wave and the significant size difference of bacteria and nanopore. The E. coli O157:H7 and S. Typhimurium were directly and simultaneously quantitated in less than 35 min without the requirement of the complex immobilization of biorecognition molecules and bacteria enrichment/separation processes. The limits of detection of E. coli O157:H7 and S. Typhimurium were 340 CFU/mL and 180 CFU/mL, respectively. The satisfied recovery rate of real samples testing verified the feasibility and accuracy of the proposed method. Our strategy not only greatly simplifies the detection and identification process of multiple pathogenic bacteria, but also is easy to extend as a universal technology for sensitive determination of other bacteria using their respective biorecognition molecules.

The GBP1 microcapsule interferes with IcsA-dependent septin cage assembly around Shigella flexneri.

Many cytosolic bacterial pathogens hijack the host actin polymerization machinery to form actin tails that promote direct cell-to-cell spread, enabling these pathogens to avoid extracellular immune defenses. However, these pathogens are still susceptible to intracellular cell-autonomous immune responses that restrict bacterial actin-based motility. Two classes of cytosolic antimotility factors, septins and guanylate-binding proteins (GBPs), have recently been established to block actin tail formation by the human-adapted bacterial pathogen Shigella flexneri. Both septin cages and GBP1 microcapsules restrict S. flexneri cell-to-cell spread by blocking S. flexneri actin-based motility. While septins assemble into cage-like structures around immobile S. flexneri, GBP1 forms microcapsules around both motile and immobile bacteria. The interplay between these two defense programs remains elusive. Here, we demonstrate that GBP1 microcapsules block septin cage assembly, likely by interfering with the function of S. flexneri IcsA, the outer membrane protein that promotes actin-based motility, as this protein is required for septin cage formation. However, S. flexneri that escape from GBP1 microcapsules via the activity of IpaH9.8, a type III secreted effector that promotes the degradation of GBPs, are often captured within septin cages. Thus, our studies reveal how septin cages and GBP1 microcapsules represent complementary host cell antimotility strategies.

Biotreatment of Cr(VI) and pyrene combined water pollution by loofa-immobilized bacteria.

Hexavalent chromium (Cr(VI)) and pyrene are toxic pollutants that are difficult to remediate from soils and wastewater. Serratia sp. strains have been previously demonstrated to remove either Cr(VI) or pyrene and here a new isolate, called the Z6 strain, was demonstrated to remove both simultaneously. The removal occurs primarily by Cr(VI) reduction and pyrene biodegradation, and genome analysis suggests the removal mechanisms are the putative chromate reductase and two assumable pathways of pyrene degradation. The Z6 strain effectively removed most Cr(VI) (up to approximately 86%) and pyrene (up to approximately 57%) in seven different types of wastewater after 7 days of biotreatment. Additionally, the carrier loofa used for bacteria immobilization did not change the kinetics of Cr(VI) reduction or pyrene degradation. The carrier loofa was also effective for multiple uses, with removal capacity not being significantly affected over the first seven cycles with the same carrier loofa. These results provide data for developing practical biotreatment applications of Cr(VI) and pyrene contaminated sites.

Biochar prepared from Fe‐rich sludge as suitable microbial carriers for facilitating biodegradation of phenanthrene in soil

AbstractBACKGROUNDConverting waste biomass to biochar by pyrolysis is increasingly recognized as an effective waste regeneration method and could be applied in contaminated soil bioremediation. In this work, we compared the properties of three biochars (FB300, FB500 and FB700) derived from iron (Fe)‐rich sludge (FS) at 300, 500 and 700 °C, and selected FB500 as microbial carrier to evaluate its function in facilitating phenanthrene (PHE) biodegradation in soil.RESULTSIncreasing pyrolysis temperature induced a positive relationship with the ash content, pH and pore size of biochars, but a negative relationship with the yield and surface area of the biochars. FB300 and FB500 maintained more organic matter than FB700, whereas, FB500 and FB700 had greater aromatic constituents and more crystal structures than FB300. Besides, FB500 showed the strongest stability and unique magnetic properties. Thus, FB500 was selected as microbial carrier in facilitating PHE biodegradation in soil. The degradation results indicated that FB500 with bacteria immobilization played a significant role in PHE degradation; its PHE removal rate of 58.15 ± 4.90% was much higher than that of 38.73 ± 3.98% for free bacteria treatment on the first day of degradation.CONCLUSIONFe‐rich sludge can be efficiently converted into biochar that in turn can serve as microbial carrier for PHE biodegradation in contaminated soil. FB500 with bacteria immobilization was proven to promote PHE degradation. Pyrolyzing Fe‐rich sludge to biochar is a promising method for remediation of PAH‐contaminated soil. © 2021 Society of Chemical Industry (SCI).

Advanced materials for immobilization of purple phototrophic bacteria in bioremediation of oil-polluted wastewater

Oil pollution which results from industrial activities, especially oil and gas industry, has become a serious issue. Cinder beats (CB), coconut fiber (CF) and polyurethane foam (PUF) are promising immobilization carriers for crude oil biodegradation because they are inexpensive, nontoxic, and non-polluting. The present investigation was aimed to evaluate this advanced technology and compare the efficiency of these immobilization carriers on supporting purple phototrophic bacterial (PPB) strains in hydrocarbon biodegradation of crude oil contaminated seawater. The surface of these biocarriers was supplemented with crude oil polluted seawater and immobilized by PPB strains, Rhodopseudomonas sp. DD4, DQ41 and FO2. Through scanning electron microscopy (SEM), the bacterial cells were shown to colonize and attach strongly to these biocarriers. The bacteria-driven carrier systems degraded over 84.2% supplemented single polycyclic aromatic hydrocarbons (PAHs). The aliphatic and aromatic components in crude oil that treated with carrier-immobilized consortia were degraded remarkably after 14 day-incubation. Among the three biocarriers, removal of the crude oil by CF-bacteria system was the highest (nearly 100%), followed by PUF-bacteria (89.5%) and CB-bacteria (86.3%) with the initial crude oil concentration was 20 g/L. Efficiency of crude oil removal by CB-bacteria and PUF-bacteria were 86.3 and 89.5%, respectively. Till now, the studies on crude oil degradation by mixture species biofilms formed by PPB on different carriers are limited. The present study showed that the biocarriers of an oil-degrading consortium could be made up of waste materials that are cheap and eco-friendly as well as augment the biodegradation of oil-contaminated seawater.

Immobilization of nitrifying bacteria on composite based on polymers and eggshells for nitrate production

Nitrification is a key step in biological nitrogen transformation which depends on the performance of specialized microorganisms. Generally, nitrifying bacteria present a low growth rate and performance which can be improved when immobilized as a biofilm. The development of new materials suitable for the immobilization of nitrifying microorganisms is very important in nitrification and wastewater treatment. In this study, the effect of eggshell powder on biofilm formation by Nitrosomonas europaea an ammonium-oxidizing bacteria and Nitrobacter vulgaris a nitrite-oxidizing bacteria, on new polymeric supports were analyzed. Polylactic acid, polyvinyl chloride and polystyrene were tested to produce polymer-eggshells powder composites and used as biofilm supports for nitrifying bacteria. The support material was characterized to identify the most suitable polymer-eggshells powder combination for the cell adhesion and biofilm formation. The nitrification results showed a highest nitrate production of 42mg NO3--N/L with polylactic acid-eggshell composite, with the best surface properties for cellular adhesion. Finally, scanning electron microscopy micrographs confirmed the best biofilm formed on polylactic acid-eggshell.

OЧИСТКА ПОЧВ ОТ НЕФТИ С ВЫСОКИМ СОДЕРЖАНИЕМ ПАРАФИНА МИКРООРГАНИЗМАМИ

This paper presents the research data aimed at resolving the problem of soil purification from high-paraffin crude oil using microorganisms.Samples of oilcontaminated soil were taken from the walls of the oil storage pit at the Uzen oilfield. According to the analysis of the oilcontaminated soil samples, the share of oil was 28 %, the share of mechanical impurities – 9.7 %, and the share of water – 60 %.It has been found that according to the API(American Petroleum Institute) indicators, that oil chemical composition may contribute to its rapid decomposition during bioremediation. Paraffin hydrocarbons are also easily decomposed by bacteria. The bacterial preparation «SHER» was used in laboratory experiments.The method of bacteria immobilization with the «SHER» biological product on the medium made from screenings of shell limestone wastes has been chosen.The conditions for conducting experimental laboratory studies on cleaning oil-contaminated soils by biological remediation are described.According to the results of the research, it was established that the immobilization of bacteria of the biological product "Sher" by a carrier in the form of sifting limestone-shell rock showed a high degree of purification of oil-contaminated soil (88.63%).To study the further activity of bacteria, experiments were conducted on the secondary use of thesolution of residual mother waterof the biological product "SHER", used in the process of cleaning oil-contaminated soil.The results of experimental studies using solution of residual mother water and immobilization by screening showed the degree of soil purification (45.7%). Thus, based on the results of studies of the drug "SHER", it can be concluded that this drug can effectively neutralize oil products in the soil.

The influence of cultivation conditions on the immobilized acetic acid bacteria metabolic activity

Brewing is an innovative sector of the food industry. Non-alcoholic beer production increases every year. The largest volumes of non-alcoholic beer are obtained by regular beer dialysis. The beer dialysate formed in production contains ethyl alcohol, which entails the need for its rational use. One of the effective ways to use beer dialysate is food biochemical vinegar production. The purpose of the work is to conduct research for biotechnology development of food vinegar from beer dialysates generation using acetic acid bacteria (AAB) immobilization on bio-carriers of various nature. The objects of research were samples of beer dialysates (BD), concentrated to a volume fraction of ethyl alcohol of 7.5%, Acetobacter aceti AAB, vinegar from BD. To study the changes in metabolic activity of immobilized AAB on a bio-carrier, acetic acid fermentation was performed using Acetobacter aceti cells, immobilized on beech shavings, zeolite, and high-pressure polyethylene. Air was supplied to a reservoir by a microcompressor from below through a finely porous ceramic nozzle, providing uniform air dispersion in cultural fluid. Graphs of the cells number and Acetobacter aceti biomass dependence on cultivation duration, nature of the bio-carrier and the aeration method when obtaining vinegar from beer dialysate are presented. The experimental data of the volatile components composition, organic acids and beer dialysate amino acids and vinegar from it are presented. Electron microscopic research of Acetobacter aceti AAB during beech shavings and zeolite cultivation is presented. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are presented.

Effects of Radiation Intensity, Mineral Matrix, and Pre-Irradiation on the Bacterial Resistance to Gamma Irradiation under Low Temperature Conditions.

Ionizing radiation is one of the main factors limiting the survival of microorganisms in extraterrestrial conditions. The survivability of microorganisms under irradiation depends significantly on the conditions, in which the irradiation occurs. In particular, temperature, pressure, oxygen and water concentrations are of great influence. However, the influence of factors such as the radiation intensity (in low-temperature conditions) and the type of mineral matrix, in which microorganisms are located, has been practically unstudied. It has been shown that the radioresistance of bacteria can increase after their exposure to sublethal doses and subsequent repair of damage under favorable conditions, however, such studies are also few and the influence of other factors of extraterrestrial space (temperature, pressure) was not studied in them. The viability of bacteria Arthrobacter polychromogenes, Kocuria rosea and Xanthomonas sp. after irradiation with gamma radiation at a dose of 1 kGy under conditions of low pressure (1 Torr) and low temperature (−50 °C) at different radiation intensities (4 vs. 0.8 kGy/h) with immobilization of bacteria on various mineral matrices (montmorillonite vs. analogue of lunar dust) has been studied. Native, previously non-irradiated strains, and strains that were previously irradiated with gamma radiation and subjected to 10 passages of cultivation on solid media were irradiated. The number of survived cells was determined by culturing on a solid medium. It has been shown that the radioresistance of bacteria depends significantly on the type of mineral matrix, on which they are immobilized, wherein montmorillonite contributes to an increased survivability in comparison with a silicate matrix. Survivability of the studied bacteria was found to increase with decreasing radiation intensity, despite the impossibility of active reparation processes under experimental conditions. Considering the low intensity of radiation on various space objects in comparison with radiobiological experiments, this suggests a longer preservation of the viable microorganisms outside the Earth than is commonly believed. An increase in bacterial radioresistance was revealed even after one cycle of irradiation of the strains and their subsequent cultivation under favourable conditions. This indicates the possibility of hypothetical microorganisms on Mars increasing their radioresistance.

Microfiber structure for enhanced immobilization of nitrifying bacteria in a post-nitrification reactor

Ammonia nitrogen in water negatively impacts aquatic life. Nitrifying bacteria are slow-growing and sensitive microorganisms, and technology using biofilm is an attractive option for their support. This study aims to demonstrate an optimal structure for microfilament carriers for growth of nitrifying bacteria in the tertiary stage of wastewater treatment (post-nitrification). Eleven samples of three polymer types (polyester, polypropylene, polyamide) that display different numbers of fibrils, fibril diameters, and structures were chosen for testing. Biofilm growth was monitored weekly using total protein concentrations and optical and fluorescence microscopy aided by image analysis. Final samples were characterized using molecular biological analysis (quantitative polymerase chain reaction and next-generation sequencing). Contents of ammonia-oxidizing bacteria (AOB) were significantly (four- to five-fold) lower than those of nitrite-oxidizing bacteria (NOB) in all tested samples. The relative abundance of NOB dominant strain, Nitrospira, reached >20%, whereas the abundance of Nitrosomonas, the only AOB representative, ranged between 3% and 6%. Polyester material was identified as optimal for support of nitrifying bacteria. This material displays maximum numbers of multifilament fibrils, and diameters of fibril and interspaces were minimal. These parameters play a crucial role for immobilization of nitrifying bacteria.

Modeling of hydrogen sulfide removal under biomethane production in the concept of renewable energy potential growth of Ukraine

Today, the global trend in the development of renewable energy sources is the implementation of integrated processing of organic waste with the production of biogenic gases such as biomethane. In this case, an essential focus is the study of biogas purification processes to methane. This paper focuses on the process of modeling biochemical purification of biogas from hydrogen sulfide to develop the direction of biomethane production. Simulation of hydrogen sulfide bio-oxidation process with the use of granulated carrier based on phosphogypsum was conducted using experimental data from previous studies to verify the adequacy of the proposed mathematical model. Thus, to implement the process of phosphogypsum utilization in technological systems of biogas purification, it is important to consider the level of bioactivity in the immobilization of bacteria on the loading surface of phosphogypsum and the degree of biotransformation of phosphogypsum components in the oxidation of carbon dioxide and hydrogen sulfide impurities to achieve the highest ecological effect. Also, the use of overlay visualization allowed to form the main clusters of development of research potential in the field of biogas technologies for Ukraine.

Use of biocompatible redox-active polymers based on carbon nanotubes and modified organic matrices for development of a highly sensitive BOD biosensor

This work investigated the use of redox-active polymers based on bovine serum albumin and chitosan, covalently bound to mediators neutral red and ferrocene and containing carbon nanotubes, for immobilization of Paracoccus yeei VKM B-3302 bacteria. The structures of produced polymers were studied by IR spectroscopy and scanning electron microscopy. Cyclic voltammetry and impedance spectroscopy found the electrochemical characteristics of the investigated systems: the heterogeneous electron transfer rate constant, the constant of the rate of interaction with P. yeei bacteria and the impedance. The systems containing carbon nanotubes and ferrocene-based redox-active polymer proved to be the most promising. Biosensors formed using the hybrid polymers had a high sensitivity with the lower boundary of 0.1 mg/dm3 of the detected BOD5 concentrations and a high correlation (R = 0.9916) with the standard BOD assay of surface water samples.

Removal of PAHs at high concentrations in a soil washing solution containing TX-100 via simultaneous sorption and biodegradation processes by immobilized degrading bacteria in PVA-SA hydrogel beads

Soil washing process enhanced by surfactants is a promising technique in removing organic pollutants from soil. In this work, a simultaneous sorption and biodegradation technique was used to remove 16 PAHs from a soil washing solution (SWS) obtained by rinsing a heavily contaminated soil from a coking plant with Triton X-100 (TX-100). This was done by immobilizing a pyrene-degrading bacterial strain in polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads. Removal performance of free bacteria, blank PVA-SA beads and beads with immobilized degrading bacteria at a low, medium and high initial concentration was evaluated. The recycling and removal performance of the used beads were also examined. Our findings showed that hydrogel beads with immobilized bacteria at a medium concentration can remove around 77% ∑16PAHs from SWS in 96 h. The beads can be recycled and reused to treat a new SWS; 32–55% ∑16PAHs was removed in 24 h. The bead provided protection for bacteria against the co-existing substances such as TX-100. The bacteria-immobilized beads are more efficient and sustainable than free bacteria and blank beads due to simultaneous sorption and biodegradation processes, thus providing a solid reference for possible industrial application of bacteria immobilization technique to deal with SWSs with complex composition.

A electrochemical biosensor for As(III) detection based on the catalytic activity of Alcaligenes faecalis immobilized on a gold nanoparticle–modified screen–printed carbon electrode

A electrochemical biosensor for As(III) determination has been developed by immobilization of the Alcaligenis faecalis bacteria on gold nanoparticle–modified screen–printed carbon electrode (AuNPs–SPCE). The detection of As(III) is due to the catalytic activity of arsenite oxidase enzyme which oxidizes As(III) to As(V) producing an analytical signal. To enhance the performance of the biosensor, was optimized the amount of bacteria, amount of glutaraldehyde and incubation time applied in the preparation of the electrode, in addition to the effect of pH and applied potential. The analytical application was carried out applying 300 mV (pH = 7) obtaining a LOD of 6.61 μmol L−1 (R = 0.9975) and 700 mV (pH = 12) obtaining a LOD of 1.84 μmol L−1 (R = 0.9983). AF/AuNPs–SPCE was applied to the determination of total arsenic in Loa river water samples after reduction, with satisfactory results.

Self-assembled cauliflower-like pyrite-S, N co-doped graphene quantum dots as free-standing anode with high conductivity and biocompatibility for bioelectricity production

Ferrous disulfide (FeS2) decorated S, N co-doped graphene quantum dots (S, N GQDs) (FeS2-S, N GQDs), were synthesized using a facile approach involving a straight hydrothermal method and tested as bioanode in acetate-feeding microbial fuel cells (MFCs) based on a mixed bacterial culture with superior performances. The physical characterizations FeS2-S, N GQDs corroborate the unique configuration that is desirable for bacteria immobilization and effective electrolyte transport. The electrochemical measurements prove the superior performance of the bifunctional electrocatalysis of FeS2-S, N GQDs for the conversion of biomass into electricity through bacteria. Significantly, at a steady-state of the power generation, the acetate-feeding MFC with FeS2-S, N GQDs as activated biomass anode delivers a maximum power density 1128 ± 9 mW/m2, which is 48% and 76% higher than the one using S, N GQDs (585 ± 7 mW/m2) and carbon cloth (265 ± 3 mW/m2) as anode electrocatalyst. With these merits, the bioanode facilitates the activity towards redox reactions of cytochromes in bacteria and exhibits higher maximum power density and stronger stability than the conventional carbon cloth. This report provides a new concept of anode electrocatalyst fabrication for the application of MFC in electricity generation.

Acetochlor degradation by a mixed culture of P. fluorescens KT3 and B. subtilis 2M6E immobilized in alginate

In this study, the acetochlor degradation by two microbial isolates, P. fluorescens KT3 and B. subtilis 2M6E, was determined. The immobilization of the bacterial mixture in alginate beads resulted in higher degradation rates compared to their free cells. The addition of glycerol as a cryoprotectant reducing adverse effects in long-term storage. After storing at 4oC for three months, the cell survivals of free cell with and without the cryoprotectant were 43.0 ± 6.1% and 57.3 ± 5.9%, while data for immobilized bacteria were 64.0 ± 5.3% and 77.6 ± 4.0%, respectively. These results prove that the immobilization of bacteria in alginate and the addition of glycerol can be applied for storing bacteria in a long-term period.

Revisiting of the physico-chemical properties of polyelectrolyte multilayers for a fine tuning of the immobilization of bacteria or nanoparticles

Increasingly used in industrial coatings, polyelectrolytes multilayers (PEMs) are self-assembled systems made of the alternate deposition of oppositely charged polymers on substrates, usually built by the traditional layer-by-layer method. Their properties strongly depend on environmental physico-chemical parameters. Due to the variety of conditions used in the literature on the one hand and the diversity of polyelectrolytes systems on the other hand, it remains difficult to bring out general principles, leading now to a lack of a real understanding of the PEM buildup, from the macro- to the nanoscale. Here, combining acoustic and electrochemical methods with atomic force microscopy, in a systematic approach, we uncover the critical role of the deposition protocol in the growth regime of PEMs made of cationic poly (allylamine hydrochloride) and anionic poly(4-styrene sulfonate, sodium). Traditional dipping leads to thick, heterogeneous and relatively isolating PEMs whereas a spin-coating assisted method leads to thinner, homogeneous and more permeable PEMs. We also highlight that the pH and the ionic strength influence not only the electrostatic interactions and polyelectrolyte conformation in solution but also their organization after their adsorption on the substrate. Finally, our easily and rapidly adaptable protocol paves the way for promising potential bio-applications, since PEMs are applied to the bacterial immobilization on substrates or as a coating for nanostructured biosensor transducer.