Concentration Of Electron Acceptor Research Articles

Optimized batch cultivation and scale-up of Bacillus thuringiensis for high-yield production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Addition of statistically optimized concentration of electron acceptor, propionic acid (1.2 g/L) at different cultivation times (0 h, 14.86 h and 19 h) during batch cultivation of B. thuringiensis in mixed substrate (glucose and glycerol) featured production of 8 g/L of biomass and 3.57 g/L of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 0.805 g/L of 3-hydroxyvalerate concentration. Successful scale up of batch cultivation from 7 L to a 70 L bioreactor was, thereafter, achieved using power/volume (P/V) criteria with maximum PHBV and biomass concentration of 3.57 g/L and 7.15 g/L respectively. Characterization of PHBV so produced was carried out using NMR, FTIR, DSC and TGA to elucidate its structure, thermal properties and stability to map their applications in society. These findings highlight the potential of the optimized batch cultivation and scale-up process in producing PHBV emphasizing its relevance in sustainable biopolymer production.

Aerobic and anaerobic mineralisation of sediment organic matter in the tidal River Elbe

PurposeThe share of microbially degradable sediment organic matter (SOM) and the degradation rate depend, among others, on the intrinsic properties of SOM as well as on the type and concentration of terminal electron acceptors (TEA). Next to its role as TEA, molecular oxygen enhances SOM decay by oxygenase-mediated breakdown of complex organic molecules. This research investigated long-term SOM decay (> 250 days) under aerobic and anaerobic conditions to (1) provide a basis for sediment carbon flux estimates from the River Elbe estuary and (2) assess the potential for carbon burial in relation to redox conditions and dredging interventions.MethodsLong-term aerobic and anaerobic SOM decay in fluid mud, pre-consolidated and consolidated sediment layers was investigated over three years along a transect of ca. 20 km through the Port of Hamburg, starting at the first hydrodynamically determined hotspot of sedimentation after the weir in Geesthacht. Absolute differences between aerobic and anaerobic cumulative carbon mineralization were calculated, as well as their ratio. Findings were correlated to a suite of solids and pore water properties.ResultsSOM decay followed first order multi-phase exponential decay kinetics. The ratio between C release under aerobic and anaerobic conditions ranged around 4 in the short-term, converging to a value of 2 in the long term. Strong gradients in absolute C release along the upstream–downstream transect did not reflect in a corresponding gradient of the aerobic-anaerobic ratio. C release was most strongly correlated to the water-soluble organic matter, in particular humic acids. Contact of anaerobically stabilized sediment with the oxygenated water phase induced significant release of carbon.ConclusionSOM degradability in the study area exhibited strong spatial gradients in relation to the organic matter source gradient but was mainly limited by the high extent of organic matter stabilization. Under these conditions, molecular oxygen as TEA provides little thermodynamic advantage. Carbon-sensitive sediment management, considering SOM reactivity patterns in stratified depositional areas, is a powerful strategy to reduce environmental impacts of dredging measures.

Microbial Ecology and Site Characteristics Underlie Differences in Salinity‐Methane Relationships in Coastal Wetlands

AbstractMethane (CH4) is a potent greenhouse gas emitted by archaea in anaerobic environments such as wetland soils. Tidal freshwater wetlands are predicted to become increasingly saline as sea levels rise due to climate change. Previous work has shown that increases in salinity generally decrease CH4 emissions, but with considerable variation, including instances where salinization increased CH4 flux. We measured microbial community composition, biogeochemistry, and CH4 flux from field samples and lab experiments from four different sites across a wide geographic range. We sought to assess how site differences and microbial ecology affect how CH4 emissions are influenced by salinization. CH4 flux was generally, but not always, positively correlated with CO2 flux, soil carbon, ammonium, phosphate, and pH. Methanogen guilds were positively correlated with CH4 flux across all sites, while methanotroph guilds were both positively and negatively correlated with CH4 depending on site. There was mixed support for negative relationships between CH4 fluxes and concentrations of alternative electron acceptors and abundances of taxa that reduce them. CH4/salinity relationships ranged from negative, to neutral, to positive and appeared to be influenced by site characteristics such as pH and plant composition, which also likely contributed to site differences in microbial communities. The activity of site‐specific microbes that may respond differently to low‐level salinity increases is likely an important driver of CH4/salinity relationships. Our results suggest several factors that make it difficult to generalize CH4/salinity relationships and highlight the need for paired microbial and flux measurements across a broader range of sites.

Kinetics of ferrihydrite reduction in a biofilm system

Microorganisms can exist in both suspended and attached forms in natural and engineered systems. While extensive research has been performed to investigate the bioreduction kinetics of iron oxides by suspended microorganisms, the kinetics of iron oxide reduction by biofilms has not been well studied. This study investigated the rates of ferrihydrite bioreduction by biofilms of Shewanella oneidensis MR-1 with variable concentration ratios of electron donor to acceptor, and different biofilm thickness. Results indicated that the bioreduction rate of ferrihydrite by biofilms increased with increasing biofilm surface area and was faster than that by suspended microorganisms for the same biomass amount, apparently as a result of the biofilm surface area facilitating the direct contact between ferrihydrite and microorganisms for electron transfer. Increasing biofilm thickness decreased bioreduction rate for the same total biomass as a result of the decrease of the ratio of the biofilm surface area to total biomass. The bioreduction rate increased with increasing electron donor and ferrihydrite inputs, consistent with the saturation type of kinetic models. The different rates of ferrihydrite reduction in the biofilm system resulted in different rates of Fe(II) production as a function of electron donor, acceptor, and biofilm surface area, which in turn affected the type and concentrations of the secondary iron minerals, such as lepidocrocite and goethite. A kinetic model was developed that integrates biofilm surface area, and electron donor and acceptor concentrations that well described the measured rates of ferrihydrite bioreduction. The results emphasized the importance of the biofilm surface area in understanding and modeling iron redox biogeochemistry and iron-related biogeochemical processes.

Enzymatic synthesis of a skin active ingredient - glochidone by 3-ketosteroid dehydrogenase from Sterolibacterium denitrificans

In this study, we applied AcmB2, sourced from Sterolibacterium denitrificans, to catalyze the oxidative dehydrogenation of 3-ketolupeol (lupenone), a derivative of lupeol, triterpene obtained from birch bark. This enzymatic Δ1-dehydrogenation catalyzed by AcmB2 yielded glochidone, a bioactive compound frequently obtained from medicinal plants like Salvia trichoclada and Maytenus boria. Glochidone is known for its broad biological activities, including antibacterial, antifungal, anti-inflammatory, anticancer, antidiabetic as well as acetylcholinesterase inhibition. Our research demonstrates >99% conversion efficiency with 100% regioselectivity of the reaction. The effective conversion to glochidone employed an electron acceptor e.g., potassium hexacyanoferrate III, in mild, environmentally friendly conditions: 8–16% 2-hydroxypropyl-β-cyclodextrin, and 2–3% 2-methoxyethanol. AcmB2 reaction optimum was determined at pH 8.0 and 30 °C. Enzyme's biochemical attributes such as electron acceptor type, concentration and steroid substrate specificity were investigated. Among 4-, 5- and 6-ring steroid derivatives androst-4-en-3,17-dione and testosterone propionate were determined as the best substrates of AcmB2. Δ1-Dehydrogenation of substrates such as lupenone, diosgenone and 3-ketopetromyzonol was confirmed. We have assessed the antioxidant and rejuvenating characteristics of glochidone as an active component in formulations, considering its precursors, lupeol, and lupenone as well. Glochidone exhibited limited antioxidant and chelating capabilities compared to lupeol and reference compounds. However, it demonstrated robust rejuvenating properties, with a sirtuin induction level of 61.5 ± 1.87%, notably surpassing that of the reference substance, E-resveratrol (45.15 ± 0.09%). Additionally, glochidone displayed 26.5±0.67 and 19.41±0.76% inhibition of elastase and collagenase, respectively. The safety of all studied triterpenes was confirmed on skin reconstructed human Epidermis model. These findings provide valuable insights into the potential applications of glochidone in formulations aimed at addressing skin health concerns. This research presents the first example of an enzyme in the 3-ketosteroid dehydrogenase (KstD) family catalyzing the Δ1-dehydrogenation of a pentacyclic triterpene. We also explored structural differences between AcmB, AcmB2, and related KstDs pointing to G52 and P532 as potentially responsible for the unique substrate specificity of AcmB2. Our findings not only highlight the enzyme's capabilities but also present novel enzymatic pathways for bioactive compound synthesis.

Modeling and Simulation of CZTS Solar Cell using Zn1-xMgxO as a buffer layer and Cul as a hole transport layer for efficiency improvement

This paper explores the impact of CZTS based solar cells using zinc magnesium oxide (Zn1-XMgXO) as a buffer layer and CuI (Copper iodide) as the hole transport layer using through SCAPS-1D(Solar Cell Capacitance Simulator) simulator. In the proposed work, the cell characteristics of the CZTS absorber layer, including electron affinity, defect density, and acceptor concentration, have been tuned. In addition, the study examines the effects of CBO which enhances the transfer of charge carriers by optimizing band alignment, Series resistance(Rs), Shunt resistance(Rsh), and Work Function (WF) of the metal contacts on the solar cell’s performance. From structures, CZTS/Zn1-XMgXO with x = 0.0652 demonstrated the highest PCE of 32.63% improvement in open circuit Voltage (Voc) = 1.0885 Volts, Short circuit density (Jsc) = 33.89, and fill factor (FF) = 88.43%.

Effect of electron acceptors on product selectivity and carbon flux in carbon chain elongation with Megasphaera hexanoica

Megasphaera hexanoica is a bacterial strain following the reverse β-oxidation pathway to synthesize caproate (CA) using lactate (LA) as an electron donor (ED) and acetate (AA) or butyrate (BA) as electron acceptors (EA). Differences in the type and concentration of EA lead to distinctions in product distribution and energy bifurcation of carbon fluxes in ED pathways, thereby affecting CA production. In this study, the effect of various ratios of AA, BA, and AA+BA as EA on carbon flux and CA specific titer during the carbon chain elongation in M. hexanoica was explored. The results indicated that the maximum levels of CA were 18.81 mM and 31.48 mM when the molar ratios of LA/AA and LA/BA were 10:1 and 3:1, respectively. Meanwhile, when AA and BA were used as combined EA (LA, AA, and BA molar amounts of 100, 23, and 77 mM), a maximum CA production of 39.45 mM was obtained. Further analysis revealed that the combined EA exhibited a CA production carbon flux of 49 % (4.3 % and 19.5 % higher compared to AA or BA, respectively) and a CA production specific titer of 45.24 mol (80.89 % and 58.51 % higher compared to AA or BA, respectively), indicating that the effective carbon utilization rate and CA production efficiency were greatly improved. Finally, a scaled-up experiment was conducted in a 1.2 L (working volume) automated bioreactor, implying high biomass (optical density at 600 nm or OD600 = 1.809) and a slight decrease in CA production (28.45 mM). A decrease in H2 production (4.11 g/m3) and an increase in CO2 production (0.632 g/m3) demonstrated the appropriate metabolic adaptation of M. hexanoica to environmental changes such as stirring shear.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Organic Solvent Contamination in Groundwater Around Natural Gas Plants

Alberta is a province that has vast deposits of natural gas. However, in its natural form it is considered sour in that it has impurities, i.e., it contains hydrogen sulphide (H2S), carbonyl sulfide (COS), carbon dioxide (CO2), mercaptans and organic sulphides. To enable the marketing of the natural gas these impurities must be removed using organic compounds and solvents. As a result of spills, leakage during processes, seepage from unlined storage ponds some of these solvents have contaminated groundwater around natural gas processing facilities. Remediation of the organic solvents is a difficult problem. To achieve an understanding of the processes involved in their degradation, a hydrogeochemical assessment of a site can be done using existing data from the site to track the development of groundwater redox zones across the different hydrostratigraphic units (HSU). This is relevant because the oxidation is hypothesized to have contributed to the biodegradation of the compounds. The objective of this global assessment is to assign a groundwater redox zone for each sample, with special emphasis placed on defining the oxidative groundwater zone (OGZ) due to its relevance to biodegradation. Ideally, the oxic groundwater zone would be defined based on the concentration of molecular oxygen (i.e., dissolved ) in groundwater (McMahon and Chapelle 2008). However, molecular oxygen, normally measured as ‘dissolved oxygen’, was not routinely measured as a field parameter in this study and therefore was unavailable to define the OGZ. The scheme adopted considers the concentrations of terminal electron acceptors (TEA) present in groundwater and measured in commonly measured parameters including oxygen, nitrate, and sulphate and dissolved metals (manganese and iron). These TEA's are consumed under progressively more reducing conditions after oxygen reduction is complete in the order: nitrate reduction, manganese reduction, iron reduction, sulphate reduction, and finally carbonate reduction (one form of methanogenesis). The results show that redox zonation is heterogeneously distributed across the site, both within and between HSUs. Multiple lines of hydrogeochemical evidence support buffered aerobic biodegradation at the site.

Superior anodic electro-fermentation by enhancing capacity for extracellular electron transfer

Anodic electro-fermentation (AEF), where an anode replaces the terminal electron acceptor, shows great promise. Recently a Lactococcus lactis strain blocked in NAD+ regeneration was demonstrated to use ferricyanide as an alternative electron acceptor to support fast growth, but the need for high concentrations of this non-regenerated electron acceptor limits practical applications. To address this, growth of this L. lactis strain, and an adaptively evolved (ALE) mutant with enhanced ferricyanide respiration capacity were investigated using an anode as electron acceptor in a bioelectrochemical system (BES) setup. Both strains grew well, however, the ALE mutant significantly faster. The ALE mutant almost exclusively generated 2,3-butanediol, whereas its parent strain mainly produced acetoin. The ALE mutant interacted efficiently with the anode, achieving a record high current density of 0.81 ± 0.05 mA/cm2. It is surprising that a Lactic Acid Bacterium, with fermentative metabolism, interacts so well with an anode, which demonstrates the potential of AEF.

CMOS-compatible electrochemical nanoimprint: High throughput fabrication of ordered microstructures on semiconductor wafer by using a glassy carbon mold

Metal assisted chemical etching (MACE), as an emerging wet chemical etching method for fabricating semiconductor micro/nano-structures (MNS), has attracted wide attentions because of the advantages of simple processes, high accuracy and no damages. However, the conventionally used noble metal catalysts (such as Au, Pt,) trapped in the micro/nano-structures are difficult to be removed or reused, not only harming the electronic performances of the CMOS devices but also increasing the fabrication cost. Here, we propose an electrochemical nanoimprint strategy by using a glassy carbon (GC) imprint mold. To overcome the poor electrocatalytic activity of GC, the GC imprint mold was connected to a Pt sheet in the cathodic chamber. To avoid the contaminations of metal and metallic cations in the fabricated MNS, the cathodic chamber was separated from the anodic one by a proton exchange membrane. By optimizing the technical parameters, including the contact pressure between GC imprint mold and GaAs wafer, the concentration of electron acceptor in the cathodic chamber, the imprinting time, etc., a remarkable corrosion rate of about 130 nm/min was achieved, comparable with that of platinum electrocatalyst. Furthermore, by using a GC imprint mold in the spatially separated corrosion cell, the contaminations caused by both the metal catalysts and metallic ions can be eliminated. Thus, this work provides a potential approach to the high throughput fabrication of CMOS-compatible semiconductor microdevices.

In Situ Enhanced Yields of Microbial Nanowires: The Key Role of Environmental Stress.

The conductive microbial nanowires of Geobacter sulfurreducens serve as a model for long-range extracellular electron transfer (EET), which is considered a revolutionary "green" nanomaterial in the fields of bioelectronics, renewable energy, and bioremediation. However, there is no efficient pathway to induce microorganisms to express a large amount of microbial nanowires. Here, several strategies have been used to successfully induce the expression of microbial nanowires. Microbial nanowire expression was closely related to the concentration of electron acceptors. The microbial nanowire was around 17.02 μm in length, more than 3 times compared to its own length. The graphite electrode was used as an alternative electron acceptor by G. sulfurreducens, which obtained a fast start-up time of 44 h in microbial fuel cells (MFCs). Meanwhile, Fe(III) citrate-coated sugarcane carbon and biochar were prepared to test the applicability of these strategies in the actual microbial community. The unsatisfied EET efficiency between c-type cytochrome and extracellular insoluble electron receptors promoted the expression of microbial nanowires. Hence, microbial nanowires were proposed to be an effective survival strategy for G. sulfurreducens to cope with various environmental stresses. Based on this top-down strategy of artificially constructed microbial environmental stress, this study is of great significance for exploring more efficient methods to induce microbial nanowires expression.

A rationale for higher ratios of CH4 to CO2 production in warmer anoxic freshwater sediments and soils

A rationale for higher ratios of <scp>CH₄</scp> to <scp>CO₂</scp> production in warmer anoxic freshwater sediments and soils

A Mathematical Model for Bioremediation of Hydrocarbon-Contaminated Soils

Bioremediation of hydrocarbons in soil is a highly complex process, involving a multiplicity of physical, chemical and biological phenomena. Therefore, it is extremely difficult to control and boost the bioremediation of these systems after an oil spill. A mathematical model was developed to assist in the prediction and decision-making regarding the in situ bioremediation of hydrocarbon-contaminated soils. The model considered the most relevant processes involved in the mass transfer and biodegradation of alkanes over time and along the depth of a flooded soil column. Aliphatic hydrocarbons were chosen since they are less water soluble than aromatics and account for 50–90% of the hydrocarbon fraction in several petroleum products. The effect of adding oxygen, nitrate, iron (III) or sulfate as electron acceptors was then simulated (bioremediation scenarios). Additionally, and to feed the model, batch assays were performed to obtain experimental data on hydrocarbon adsorption to soil particles (more than 60% of hydrocarbons tends to be adsorbed to soil particles), as well as hydrocarbon biodegradation rates in the presence of nitrate (0.114 d−1) and oxygen (0.587 d−1). The model indicates that saturated hydrocarbon removal occurs mainly with adsorption/desorption and transport processes in the upper layers of soil due to methanogenic biodegradation in deeper layers, since the other microbial processes are soon limited by the lack of electron acceptors. Simulation results show that higher initial electron acceptor concentrations led to higher hydrocarbon removal, confirming that the model is performing in accordance with the expected. Close to the surface (at 0.1 m depth), all scenarios predicted more than 83% hydrocarbon removal after two years of simulation. Soil re-aeration results in faster hydrocarbon removal (more than 20% after one year) and surfactants addition (around 15% after one year) may also accelerate soil bioremediation. With this model, the simultaneous contributions of the various physicochemical and biological processes are integrated, facilitating the simulation and comparison of different bioremediation scenarios. Therefore, it represents a useful support tool for the management of contaminated sites.

Organic carbon metabolism is a main determinant of hydrogen demand and dynamics in anaerobic soils.

Hydrogen (H2) is a crucial electron donor for many processes in the environment including nitrate-, sulfate- and, iron-reduction, homoacetogenesis, and methanogenesis, and is a major determinant of microbial competition and metabolic pathways in groundwater, sediments, and soils. Despite the importance of H2 for many microbial processes in the environment, the total H2 consuming capacity (or H2 demand) of soils is generally unknown. Using soil microcosms with added H2, the aims of this study were 1) to measure the H2 demand of geochemically diverse soils and 2) to define the processes leading to this demand. Study results documented a large range of H2 demand in soil (0.034-1.2 millielectron equivalents H2 g-1 soil). The measured H2 demand greatly exceeded the theoretical demand predicted based on measured concentrations of common electron acceptors initially present in a library of 15 soils. While methanogenesis accounted for the largest fraction of H2 demand, humic acid reduction and acetogenesis were also significant contributing H2-consuming processes. Much of the H2 demand could be attributed to CO2 produced during incubation from fermentation and/or acetoclastic methanogenesis. The soil initial total organic carbon showed the strongest correlation to H2 demand. Besides external additions, H2 was likely generated or cycled in the microcosms. Apart from fermentative H2 production, carboxylate elongation to produce C4-C7 fatty acids may have accounted for additional H2 production in these soils. Many of these processes, especially the organic carbon contribution is underestimated in microbial models for H2 consumption in natural soil ecosystems or during bioremediation of contaminants in soils.

Microbiologically influenced corrosion of stainless steels by Bacillus subtilis via bidirectional extracellular electron transfer

The corrosion of 304 stainless steel by Bacillus subtilis was investigated under different glycerol (electron donor) and nitrate (electron acceptor) concentrations. When nitrate was deficient, the passive film served as an alternative electron acceptor to complete outward extracellular electron transfer (EET) of B. subtilis, inducing more severe corrosion especially in the early stage. When glycerol concentration was deficient, the inward EET of B. subtilis was significantly enhanced, resulting in accelerated corrosion in the late stage. These results demonstrated that bidirectional EET was involved in the corrosion of stainless steel by B. subtilis and depended on the electron donor/acceptor concentrations.

Dynamic roles of inner membrane electron-transfer hub of Shewanella oneidensis MR-1 in response to extracellular reduction kinetics

The unique extracellular electron transfer (EET) network of exoelectrogens endow them with extraordinary extracellular respiration ability to facilitate environmental remediation and biogeochemical processes. Shewanella oneidensis MR-1 is an environmentally ubiquitous exoelectrogen possessing multiple EET pathways. While the inner membrane CymA protein is widely believed to serve as an essential electron transfer hub in all these pathways, here our experimental evidences suggest another possibility: its EET role is highly dependent on extracellular reduction kinetics. Comparison of the bacterial EET and extracellular reduction performances in response to different species and concentrations of extracellular electron acceptors shows that the fraction of electron efflux contributed by the CymA pathway is positively correlated to the EET rate. This means some unknown EET pathways independent of CymA are activated under slow EET condition, likely as a strategy of self-adaption to environmental changes by feedback regulating the electron transport pathways. Our findings provide a new perspective to facilitate better understanding of the dynamic bacteria-environment interactions, and may inspire the discovery of new EET proteins and the development of more environmentally-robust biotechnologies for environmental remediation applications.

Improving methane mitigating functionality of blast furnace slag by adding electron acceptor

Blast furnace slag (BFS), a byproduct of iron-producing process, has been applied as silicate fertilizer in rice paddy. Silicate fertilizer contains lime and silicate as main components and iron and manganese as electron acceptors. This amendment improves soil productivity and mitigates methane (CH4) emissions. However, its suppression effect was limited to <20 % at a field level, and its functionality needs improvement to encourage recycling. We hypothesized that the effect of silicate fertilizer on suppressing CH4 emission might improve by increasing electron acceptor concentration. To investigate the feasibility of electron acceptor added silicate fertilizer on increasing CH4 flux suppression, four byproducts of the iron-production process (basic oxygen slag-BOF, ferromanganese slag-FerroMn, iron rust, and Kambara reactor slag-KR) were selected and compared through soil incubation test. Iron rust effectively suppressed CH4 production by 67 %, which is comparable with a 15–30 % reduction of others. To find the optimum mixing ratio of iron rust, it was mixed to BFS with the rate of 0–5 % (wt wt−1), and their effect on CH4 flux was compared. The 3 % mixing ratio highly increased the BFS functionality on suppressing CH4 production. To confirm the field adaptability of the improved BFS, three types of silicate fertilizer (mixing iron rust with the ratios of 0, 2.5, and 5 %) were applied with the recommendation level (1.5 Mg ha−1) before rice transplanting. Seasonal CH4 flux was significantly decreased by the original silicate fertilizer (BFS0) application to 20 % over control. This effectiveness was enhanced by adding 2.5 % iron rust but thereafter, not more increased. Silicate fertilization (BFS0) significantly increased rice grain productivity by 9 % over control, and the improved silicate fertilizer (BFS2.5 & 5.0) more highly increased by 13 %. In conclusion, the BFS's functionality to increase rice productivity and suppress CH4 emission could be improved by adding an effective electron acceptor such as Fe2O3.

Enhancing the sensitivity of water toxicity detection based on suspended Shewanella oneidensis MR-1 by reversing extracellular electron transfer direction.

Water toxicity detection is of great significance to ensure the safety of water supply. With suspended electrochemically active bacteria (EAB) as the sensing element, a novel microbial electrochemical sensor (MES) has recently been reported for the real-time detection of water toxicity, but its practical applications need to further improve the sensitivity. Extracellular electron transfer (EET) is an important factor affecting MES performance. In the study, the EET of suspended EAB-based MES was optimized to further enhance the sensitivity. Firstly, by using a model EAB stain Shewanella oneidensis MR-1, it was revealed that the sensitivity was increased at most 2.7 times with inward EET (i.e., cathodic polarization). Then, a novel conjecture based on electron transfer and energy fluxes was proposed and testified to explain this phenomenon. Finally, three key operating parameters of inward EET were orthogonally optimized. The optimized parameters of inward EET included a potential of - 0.5V, a cell density of 1.8 × 108CFU/mL, and an electron acceptor concentration of 15mM.

Spatial–temporal assessment of hydrocarbon biodegradation mechanisms at a contaminated groundwater site in Serbia

ABSTRACT The characterization and cleanup of groundwater contamination in hazardous-waste sites are of significant engineering and scientific importance. This study analyzes biodegradation fingerprints in groundwater, 25 years after the accidental leakage of kerosene (jet fuel) at the site in central Serbia. The long-term existence of hydrocarbon contamination and the presence of indigenous microbiological populations capable of biodegradation have been confirmed by the results of GCxGC-MS chromatography and microbiological characterization. Total petroleum hydrocarbons (TPH), geochemical indicators, and other parameters were spatially analyzed to provide insight into biodegradation occurrence. The lowest concentrations of electron acceptors (O2, NO3 -, and SO4 2-) and the highest concentrations of microbial metabolic products (Mn and Fe) overlap in the piezometers closest to the source of contamination, due to the occurrence of different biodegradation mechanisms. Based on the analysis of redox-sensitive compounds, the mixed oxic-anoxic processes in groundwater also correspond to the aforementioned zone, as confirmed by the redox potential (Eh) measurements. The results of cross-study analysis reveal further reduction of hydrocarbon contamination, the occurrence of less anoxic redox processes, and the increase of oxic conditions in groundwater. Overall, the results provide clear evidence of the biodegradation effects in groundwater and insight into their evolution under natural attenuation processes.