Characterization and significance of extracellular polymeric substances, reactive oxygen species, and extracellular electron transfer in methanogenic biocathode.
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ABSTRACT:
SUBMITTER: Zakaria BS
PROVIDER: S-EPMC8041852 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Microorganisms exploit extracellular electron transfer (EET) in growth and information exchange with external environments or with other cells. Every microbial cell is surrounded by extracellular polymeric substances (EPS). Understanding the roles of three-dimensional (3D) EPS in EET is essential in microbiology and microbial exploitation for mineral bio-respiration, pollutant conversion, and bioenergy production. We have addressed these challenges by comparing pure and EPS-depleted samples of three representative electrochemically active strains viz Gram-negative Shewanella oneidensis MR-1, Gram-positive Bacillus sp. WS-XY1, and yeast Pichia stipites using technology from electrochemistry, spectroscopy, atomic force microscopy, and microbiology. Voltammetry discloses redox signals from cytochromes and flavins in intact MR-1 cells, whereas stronger signals from cytochromes and additional signals from both flavins and cytochromes are found after EPS depletion. Flow cytometry and fluorescence microscopy substantiated by N-acetylglucosamine and electron transport system activity data showed less than 1.5% cell damage after EPS extraction. The electrochemical differences between normal and EPS-depleted cells therefore originate from electrochemical species in cell walls and EPS. The 35 ± 15-nm MR-1 EPS layer is also electrochemically active itself, with cytochrome electron transfer rate constants of 0.026 and 0.056 s-1 for intact MR-1 and EPS-depleted cells, respectively. This surprisingly small rate difference suggests that molecular redox species at the core of EPS assist EET. The combination of all the data with electron transfer analysis suggests that electron "hopping" is the most likely molecular mechanism for electrochemical electron transfer through EPS.
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Project description:Antibiotic resistance genes (ARGs) in bacteria are emerging contaminants as their proliferation in the environment poses significant threats to human health. It is well recognized that extracellular polymeric substances (EPS) can protect microorganisms against stress or damage from exogenous contaminants. However, it is not clear whether EPS could affect the lateral transfer of ARGs into bacteria, which is one of the major processes for the dissemination of ARGs. This study investigated the lateral transfer of ARGs carried by plasmids (pUC19, pHSG298, and pHSG396) into competent Escherichia coli cells with and without EPS. Transformant numbers and transformation efficiency for E. coli without EPS were up to 29 times of those with EPS at pH 7.0 in an aqueous system. The EPS removal further increased cell permeability in addition to the enhanced cell permeability by Ca2+, which could be responsible for the enhanced lateral transfer of ARGs. The fluorescence quenching experiments showed that EPS could strongly bind to plasmid DNA in the presence of Ca2+ and the binding strength (LogK A = 10.65-15.80 L mol-1) between EPS and plasmids was positively correlated with the enhancement percentage of transformation efficiency resulting from the EPS removal. X-ray photoelectron spectroscopy (XPS) analyses and model computation further showed that Ca2+ could electrostatically bind with EPS mainly through the carboxyl group, hydroxyl group, and RC-O-CR in glucoside, thus bridging the plasmid and EPS. As a result, the binding of plasmids with EPS hindered the lateral transfer of plasmid-borne ARGs. This study improved our understanding on the function of EPS in controlling the fate and transport of ARGs on the molecular and cellular scales.
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Project description:Apical periodontitis is frequently associated with the presence of bacteria biofilm, which has an indisputable impact on the prognosis of endodontic therapy due to the high resistance to adverse environmental conditions, chemicals, and antibiotic therapy that characterize bacteria within biofilm. The biofilm matrix acts as a protective shield over the encased microorganisms. The aim of this investigation was to identify the main biochemical components of biofilm matrix from endodontic mono- and dual-species biofilms. Enterococcus faecalis and Actinomyces naeslundii were cultured as mono- and dual-species biofilms for 14 days. Crude extracellular polymeric substances (EPSs) from biofilm matrices were extracted using chemical and physical methods. High-performance liquid chromatography, gas chromatography, and mass spectrometry were used to determine the carbohydrate, protein, and fatty acid components. Chemical analysis of the biofilm matrices revealed that they were mainly composed of stachyose, maltose, and mannose carbohydrates. The protein profile in all biofilm samples showed abundant oxidoreductases and chaperone proteins and some virulence- associated proteins mainly located in the membrane surface. High percentages of saturated and monounsaturated fatty acids were identified in all biofilm matrices, with a major prevalence of palmitic, stearic, and oleic acids. Based on the results, it was possible to obtain for the first time a general overview of the biochemical profile of endodontic biofilm matrices.
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Project description:Although the capacity for electroactive bacteria to convert environmental metallic minerals and organic pollutants is well known, the role of the redox properties of microbial extracellular polymeric substances (EPS) in this process is poorly understood. In this work, the redox properties of EPS from two widely present electroactive bacterial strains (Shewanella oneidensis and Pseudomonas putida) were explored. Electrochemical analysis demonstrates that the EPS extracted from the two strains exhibited redox properties. Spectroelectrochemical and protein electrophoresis analyses indicate that the extracted EPS from S. oneidensis and P. putida contained heme-binding proteins, which were identified as the possible redox components in the EPS. The results of heme-mediated behavior of EPS may provide an insight into the important roles of EPS in electroactive bacteria to maximize their redox capability for biogeochemical cycling, environmental bioremediation and wastewater treatment.
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Project description:The specific roles of extracellular polymeric substances (EPS) and how factors influenced EPS's roles during U(VI) immobilization are still unclear. In this study, high content of U with the main form of nanoparticles was detected in EPS, accounting for 10-42% of total U(VI) removal. EPS might be utilized as energy source or even as electron donors when external carbon source was unavailable. The influencing degree of each experimental parameter to uranium (U) removal process was elucidated. The influential priority to U(IV)/U(VI) ratios in sludge was as follows: acetate, U(VI), and nitrate. The influential priority to total EPS contents was as follows: U(VI), nitrate and acetate. The complex interaction mechanism between U(VI) and EPS in the U immobilization process was proposed, which might involve three ways including biosorption, bioreduction and bioprecipitation. These results indicate important and various roles of EPS in U(VI) immobilization.
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Project description:The recovery of biopolymers from the waste sludge produced in wastewater treatments and their application in other industrial sectors, would substantially increase the environmental and economical sustainability of the process, promoting the development of a circular economy. In this study, extracellular polymeric substances (EPS) extracted from anammox granular waste sludge, were investigated and characterized. Rheological and differential scanning calorimetry measurements on EPS aqueous dispersions indicate the formation of an extended 3-D network above a threshold concentration, with a clear dependence of the mechanical and water retention properties on EPS content. The structural characterization, performed with transmission electron microscopy and small angle X-ray scattering, reveals the presence of functional amyloids as putative structural units, observed for the first time in an EPS-based hydrogel. As a proof of concept of the applicative potential, we explored the water and grease resistance provided to paper by an EPS coating. These results shed light on the structural details of EPS-based hydrogels, and pave the way for the possible use of EPS-based materials as a cheap, eco-friendly alternative to commonly adopted paper coatings, in line with a circular economy pattern for wastewater treatment.
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Project description:Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reactor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consortia. The aggregates were electrically conductive, with conductivities 3-fold higher than the conductivities previously reported for dual-species aggregates of Geobacter species in which the two species appeared to exchange electrons via interspecies electron transfer. The temperature dependence response of the aggregate conductance was characteristic of the organic metallic-like conductance previously described for the conductive pili of Geobacter sulfurreducens and was inconsistent with electron conduction through minerals. Studies in which aggregates were incubated with high concentrations of potential electron donors demonstrated that the aggregates had no significant capacity for conversion of hydrogen to methane. The aggregates converted formate to methane but at rates too low to account for the rates at which that the aggregates syntrophically metabolized ethanol, an important component of the reactor influent. Geobacter species comprised 25% of 16S rRNA gene sequences recovered from the aggregates, suggesting that Geobacter species may have contributed to some but probably not all of the aggregate conductivity. Microorganisms most closely related to the acetate-utilizing Methanosaeta concilii accounted for more than 90% of the sequences that could be assigned to methane producers, consistent with the poor capacity for hydrogen and formate utilization. These results demonstrate for the first time that methanogenic wastewater aggregates can be electrically conductive and suggest that direct interspecies electron transfer could be an important mechanism for electron exchange in some methanogenic systems.
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Project description:To investigate how cell elongation impacts extracellular electron transfer (EET) of electroactive microorganisms (EAMs), the division of model EAM Shewanella oneidensis MR-1 was engineered by reducing the formation of cell divisome. Specially, by blocking the translation of division proteins via anti-sense RNAs or expressing division inhibitors, the cellular length and output power density were all increased. Electrophysiological and transcriptomic results synergistically revealed that the programmed cell elongation reinforced EET by enhancing NADH oxidation, inner-membrane quinone pool, and abundance of c-type cytochromes. Moreover, cell elongation enhanced hydrophobicity due to decreased cell-surface polysaccharide, thus facilitated initial surface adhesion stage in biofilm formation. The output current and power density all increased in positive correction with cellular length. However, inhibition of cell division reduced cell growth, which was then restored by quorum sensing-based dynamic regulation of cell growth and elongation phases. The QS-regulated elongated strain thus enabled a cell length of 143.6 ± 40.3 µm (72.6-fold of that of S. oneidensis MR-1), which resulted in an output power density of 248.0 ± 10.6 mW m-2 (3.41-fold of that of S. oneidensis MR-1) and exhibited superior potential for pollutant treatment. Engineering cellular length paves an innovate avenue for enhancing the EET of EAMs.
2024-09-25 | GSE244261 | GEO
Project description:Four sponge-associated Antarctic bacteria (i.e., Winogradskyella sp. strains CAL384 and CAL396, Colwellia sp. strain GW185, and Shewanella sp. strain CAL606) were selected for the highly mucous appearance of their colonies on agar plates. The production of extracellular polymeric substances (EPSs) was enhanced by a step-by-step approach, varying the carbon source, substrate and NaCl concentrations, temperature, and pH. The EPSs produced under optimal conditions were chemically characterized, resulting in a moderate carbohydrate content (range, 15 to 28%) and the presence of proteins (range, 3 to 24%) and uronic acids (range, 3.2 to 11.9%). Chemical hydrolysis of the carbohydrate portion revealed galactose, glucose, galactosamine, and mannose as the principal constituents. The potential biotechnological applications of the EPSs were also investigated. The high protein content in the EPSs from Winogradskyella sp. CAL384 was probably responsible for the excellent emulsifying activity toward tested hydrocarbons, with a stable emulsification index (E24) higher than those recorded for synthetic surfactants. All the EPSs tested in this work improved the freeze-thaw survival ratio of the isolates, suggesting that they may be exploited as cryoprotection agents. The addition of a sugar in the culture medium, by stimulating EPS production, also allowed isolates to grow in the presence of higher concentrations of mercury and cadmium. This finding was probably dependent on the presence of uronic acids and sulfate groups, which can act as ligands for cations, in the extracted EPSs.IMPORTANCE To date, biological matrices have never been employed for the investigation of EPS production by Antarctic psychrotolerant marine bacteria. The biotechnological potential of extracellular polymeric substances produced by Antarctic bacteria is very broad and comprises many advantages, due to their biodegradability, high selectivity, and specific action compared to synthetic molecules. Here, several interesting EPS properties have been highlighted, such as emulsifying activity, cryoprotection, biofilm formation, and heavy metal chelation, suggesting their potential applications in cosmetic, environmental, and food biotechnological fields as valid alternatives to the commercial polymers currently used.
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Project description:Extracellular polymeric substances (EPS) play important roles in regulating the dewaterability of sludge. This study sought to elucidate the influence of EPS on the dewaterability of sludge during bioleaching process. Results showed that, in bioleaching system with the co-inoculation of Acidithiobacillus thiooxidans TS6 and Acidithiobacillus ferrooxidans LX5 (A. t+A. f system), the capillary suction time (CST) of sludge reduced from 255.9 s to 25.45 s within 48 h, which was obviously better than the controls. The correlation analysis between sludge CST and sludge EPS revealed that the sludge EPS significantly impacted the dewaterability of sludge. Sludge CST had correlation with protein content in slime and both protein and polysaccharide contents in TB-EPS and Slime+LB+TB layers, and the decrease of protein content in slime and decreases of both protein and polysaccharide contents in TB-EPS and Slime+LB+TB layers improved sludge dewaterability during sludge bioleaching process. Moreover, the low sludge pH (2.92) and the increasing distribution of Fe in the solid phase were another two factors responsible for the improvement of sludge dewaterability during bioleaching. This study suggested that during sludge bioleaching the growth of Acidithiobacillus species resulted in the decrease of sludge pH, the increasing distribution of Fe in the solid phase, and the decrease of EPS content (mainly including protein and/or polysaccharide) in the slime, TB-EPS, and Slime+LB+TB layers, all of which are helpful for sludge dewaterability enhancement.
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