Electron Donor Source Research Articles

Whole-cell biocatalysis using the Acidovorax sp. CHX100 Δ6HX for the production of ω-hydroxycarboxylic acids from cycloalkanes

Omega hydroxycarboxylic acids (ω-HAs) possess two functional groups, a hydroxyl group and a carboxyl group, and are essential precursors for the production of biodegradable polyester polymers. In this work, an Acidovorax mutant was investigated as a whole-cell biocatalyst for the conversion of cycloalkanes to their respective ω-hydroxycarboxylic acids. This Acidovorax sp. strain CHX100 originated from a wastewater treatment plant and uses cyclohexane as the sole source of carbon and energy with excellent growth rates (0.199 h-1). The metabolic efficiency of Acidovorax CHX100 is based on a highly efficient enzyme cascade used for the mineralization of cyclohexane. A deletion of 6-hydroxyhexanoate dehydrogenase in the native cycloalkane pathway resulted in the Acidovorax sp. strain CHX100 Δ6HX mutant, which accumulated short ω-hydroxycarboxylic acids (C5 to C10) from cycloalkanes. This mutant transformed cyclopentane and cyclohexane (5 mM) to 5-hydroxypentanoic acid and 6-hydroxyhexanoic acid, respectively, with a molar conversion above 98% in 6 h. An elementary environmental and economical assessment based on E-factor and biocatalyst yield suggests the use of inexpensive electron donor and carbon sources, with subsequent efforts to minimize waste generation. Such an early-stage analysis highlights the main bottlenecks that need to be solved in developing a sustainable bioprocess.

Kinetics and mechanism of radium-isotopes dissolution in TENORM scale waste associated with petroleum production using certain organic carbon source: lactic acid solution-case study.

The present study is conducted to explore the dissolution as inferred from the kinetic mechanism for radium-isotopes (228Ra, 226Ra, and 224Ra) in the TENORM scale waste deposited in oilfield pipes and equipment, Gulf of Suez, Egypt. The main efficiency factors for Ra2+-compound dissolution by lactic acid (LA) solution, e.g., reactive organic carbon (i.e., electron-donor source), have been investigated, and optimum chemical conditions have been determined. The obtained data were also employed to predict the leaching kinetics and mechanism of the Ra2+-isotopes removal by three shrinking core models (SCM, liquid film process-chemical controlled process-diffusion controlled process) and Arrhenius model. The maximum leaching percentage of Ra2+-isotopes reached to 55-60% at the optimal leaching conditions (0.3M LA, 5h, 25°C, ϕ < 1mm, S/L ratio 10/50gmL-1). The Ra-isotopes removal proceeds kinetically by diffusion-controlled process. Activation energy (Ea) of the leaching process was 10.51kJmol-1. This value conforms that the leaching process for removal of Ra2+-isotopes in the TENORM scale waste by LA solution is controlled by a diffusion process. Values of thermodynamic parameters (∆Go,∆Ho,∆So) were determined and indicate that dissolution of Ra2+-isotopes in the studied waste is non-spontaneous and temperature dependent. Moreover, the leaching mechanism may be attributed to the dissolution of soluble exchangeable and acidic species of Ra2+-species and/or these due conversions of insoluble Ra-sulfate to more soluble Ra-sulfide and/or Ra-hydrogen sulfide by LA solutions.

The hidden chemolithoautotrophic metabolism of Geobacter sulfurreducens uncovered by adaptation to formate.

Multiple Fe(III)-reducing Geobacter species including the model Geobacter sulfurreducens are thought to be incapable of carbon dioxide fixation. The discovery of the reversed oxidative tricarboxylic acid cycle (roTCA) for CO2 reduction with citrate synthase as key enzyme raises the possibility that G. sulfurreducens harbors the metabolic potential for chemolithoautotrophic growth. We investigate this hypothesis by transferring G. sulfurreducens PCA serially with Fe(III) as electron acceptor and formate as electron donor and carbon source. The evolved strain T17-3 grew chemolithoautotrophically with a 2.7-fold population increase over 48 h and a Fe(III) reduction rate of 417.5 μM h-1. T17-3 also grew with CO2 as carbon source. Mutations in T17-3 and enzymatic assays point to an adaptation process where the succinyl-CoA synthetase, which is inactive in the wild-type, became active to complete the roTCA cycle. Deletion of the genes coding for the succinyl-CoA synthetase in T17-3 prevented growth with formate as substrate. Enzymatic assays also showed that the citrate synthase can perform the necessary cleavage of citrate for the functional roTCA cycle. These results demonstrate that G. sulfurreducens after adaptation reduced CO2 via the roTCA cycle. This previously hidden metabolism can be harnessed for biotechnological applications and suggests hidden ecological functions for Geobacter.

Electron Transfer Mediated by Iron Carbonyl Clusters Enhance Light-Driven Hydrogen Evolution in Water by Quantum Dots.

Photocatalytic water splitting has become a promising strategy for converting solar energy into clean and carbon‐neutral solar fuels in a low‐cost and environmentally benign way. Hydrogen gas is such a potential solar fuel/energy carrier. In a classical artificial photosynthetic system, a photosensitizer is generally associated with a co‐catalyst to convert photogenerated charge into (a) chemical bond(s). In the present study, assemblies consisting of CdSe quantum dots that are coupled with one of two molecular complexes/catalysts, that is, [Fe2S2(CO)6] or [Fe3Te2(CO)9], using an interface‐directed approach, have been tested as catalytic systems for hydrogen production in aqueous solution/organic solution. In the presence of ascorbic acid as a sacrificial electron donor and proton source, these assemblies exhibit enhanced activities for the rate of hydrogen production under visible light irradiation for 8 h in aqueous solution at pH 4.0 with up to 110 μmol of H2 per mg of assembly, almost 8.5 times that of pure CdSe quantum dots under the same conditions. Transient absorption and time‐resolved photoluminescence spectroscopies have been used to investigate the charge carrier transfer dynamics in the quantum dot/iron carbonyl cluster assemblies. The spectroscopic results indicate that effective electron transfer from the molecular iron complex to the valence band of the excited CdSe quantum dots significantly inhibits the recombination of photogenerated charge carriers, boosting the photocatalytic activity for hydrogen generation; that is, the iron clusters function as effective intermediaries for electron transfer from the sacrificial electron donor to the valence band of the quantum dots.

Power to hydrogen-oxidizing bacteria: Effect of current density on bacterial activity and community spectra

Hydrogen-oxidizing bacteria (HOB) can utilize hydrogen, oxygen, and carbon dioxide as electron donor, electron acceptor, and carbon source, respectively. These bacteria can convert hydrogen and carbon dioxide to biomass which is different from hydrophilic denitrification. “Power to HOB”, a new supplementary to “Power to Gas”, was proposed and demonstrated in this study, in which HOB were cultivated via in-situ consuming hydrogen generated by water electrolysis. The objects of this work were to explore the effect of current density on HOB activity and microbial community. The results showed good activity of enriched HOB that the nitrate consumption rate was 21 mg/L/d in batch and continuous modes under the current density (CD) of 2.14 mA/cm2. The cyclic voltammetry curve demonstrated the electric activity of HOB that redox peaks were 0.330 V and 0.195 V at corresponding CDs of 2.14 mA/cm2 and 4.29 mA/cm2, respectively. Finally, the community spectra revealed that the percentage of Cupriavidus sp. TA19 decreased by 15.59% (2.14 mA/cm2 vs 4.29 mA/cm2), and Pseudonocardia sp. YK32 increased by 38.31%. Moreover, Cupriavidus sp. TA19 was reported as HOB for polyhydroxyalkanoate (PHA, degradable plastics) production. Pseudonocardia sp. YK32 was also reported as HOB and the function was unknown. Thus, “Power to HOB” can be a new supplementary to “Power to Gas” and the results extend HOB applications.

Bio-reduction of ferrihydrite-montmorillonite-organic matter complexes: Effect of montmorillonite and fate of organic matter

Organic matter (OM) is often associated with Fe (hydr)oxides such as ferrihydrite (Fh) in soils and sediments, forming binary Fh-OM complexes. Microbial reduction of Fh results in destabilization of the complexes and mineral/OM transformation. However, little is known about the role of clay minerals in such processes, despite their common co-existence with Fh and OM in natural environments. Here Fh-OM complexes were synthesized in the presence of montmorillonite (SWy-2), forming ternary Fh-(SWy-2)-OM complexes. A metal-reducing bacterium Geobacter sulfurreducens was used to reduce Fh in the complexes under circumneutral pH and anoxic conditions with or without H2 as extra electron donor. Various spectroscopy and mass spectrometry methods were used to monitor the progress of Fh bio-reduction and mineral/OM transformation. Results showed that G. sulfurreducens utilized mineral-bound OM as electron donor and/or carbon source to couple with Fh reduction. Relative to Fh-OM complex, addition of SWy-2 to Fh-OM complex enhanced the bio-reduction extent of Fh by increasing the proportion of bioavailable OM that was weakly bound to SWy-2. However, its effect on the bio-reduction rate was variable. SWy-2 initially decreased the rate, because it spatially separated OM (electron donor) from Fh (electron acceptor). During later incubation, SWy-2 increased the reduction rate by sorbing biogenic Fe2+ that would otherwise passivate the Fh and cell surfaces. Bio-reduction transformed mineral-bound OM to microbial products (e.g. necromass, extracellular polymeric substances), but organic compounds with aromatic structures, carboxyl groups and large molecular weight were more resistant to desorption and oxidation. The persistence of these compounds against bio-reduction induced transformation is likely due to their stronger binding with minerals and/or lower nominal oxidation states of carbon relative to other compounds. Our results provide new insights into the role of clay minerals in regulating biogeochemical cycling of solid-phase Fe and transformation of mineral-associated OM in anoxic soil environments.

Hydrogen production from natural organic matter via cascading oxic-anoxic photocatalytic processes: An energy recovering water purification technology

Photocatalysis provides a “green” strategy to produce the clean energy of H2. However, the realization of efficient H2 production is usually accomplished by the consumption of electron donors, which are costly energy carriers themselves. Here, we attempted to utilize the naturally abundant humic acid (HA), a representative natural organic matter (NOM), as the source of electron donor in a cascading oxic-anoxic photocatalytic system. Results showed that degradation of HA and remarkable H2 yield (1660.9 μmol g−1 h−1 at optimal condition) were obtained successively, whereas the anoxic photocatalytic treatment of pristine HA did not improve H2 yield but substantially eliminated the H2 production and HA degradation efficiency. These phenomena suggested the preoxidation process played a vital role in counteracting the detrimental effect of HA on photocatalytic H2 production. Electrochemical measurement indicated that the preoxidized HA harbored more redox-active moieties than the untreated HA and thus leading to a higher photo-induced charge carrier separation efficiency. A variety of advanced spectroscopic analyses revealed that the photocatalytic oxic pre-treatment resulted in breakdown of chemically inert, electron mediating and chromophoric aromatic macrostructure of HA to form smaller sized oxygenated organic intermediates. These intermediates were more nucleophilic than the pristine HA and acted as sacrificial reagent in the subsequent anoxic process for boosting H2 production. This study showcases an energy recovering water remediation process and paves the way for the design of novel photocatalytic technologies for environmental application.

A highly mismatched NiO2-to-Pd hetero-structure as an efficient nanocatalyst for the hydrogen evolution reaction

NiO2 base crystal serves as an electron donor source which injects electrons to Pd nanocrystals by strong electronegativity difference and lattice strain. It creates a high density of active sites on the NC surface and thus improves the HER kinetics.

Isolation and Characterization of a Molybdenum-reducing and Coumaphos-degrading Bacillus sp. strain Neni-12 in soils from West Sumatera, Indonesia

The inappropriate removal, manufacturing and prospecting actions and unnecessary use of agricultural chemical compounds have triggered an international issue. Eliminating these kinds of contaminants by means of bioremediation is a less expensive approach in the long term notably at low concentrations, in which various other approaches for instance physical or chemical approaches is probably not useful. In this work we screen the ability of a molybdenum-reducing bacterium isolated from polluted soil to make use of pesticides as electron donor sources for assisting reduction and as carbon sources for growth. The bacterium was not able to use pesticides as electron donors, nonetheless, the bacterium can grow on coumaphos separate from molybdenum reduction. Optimum conditions for Mo-blue production were at pH 6.3 and between 25 and 37 oC, glucose as electron donor, phosphate at 5.0 mM and sodium molybdate between 15 and 20 mM. Reduction was inhibited by Hg, Ag and Cr at 2 ppm by 91.9, 82.7 and 17.4 %, respectively. Biochemical analysis tentatively and partially identified the bacterium as Bacillus sp. strain Neni-12. This is a novel Mo-reducing bacterium with coumaphos degrading capability.

Anaerobic production of valeric acid from crude glycerol via chain elongation

Glycerol from biodiesel production was used as a substrate for valerate production in a 13.1-L anaerobic filter with an open microbiome. Ethanol at 15% of the influent chemical oxygen demand was supplemented as an additional electron donor source. The 114-day experimental period was divided in three phases which included initial adaptation phase, external sludge addition from a caproic acid producing reactor and valerate extraction using a pertraction system. Propionate (0.63–1.75 g COD L−1 day−1) and valerate (0.86–1.81 g COD L−1 day−1) were the main carboxylates formed throughout all operational phases. An increase in production rates of butyrate (0.26–0.31 g COD L−1 day−1), caproate (0.01–0.08 g COD L−1 day−1), and 1,3-propanediol (0.43–0.52 g COD L−1 day−1) was observed with addition of external caproic acid producing sludge rich in Clostridium members. In the operational phase with pertraction, a sudden decrease in 1,3-propanediol and concomitant increase in acid production were verified. Propionate and valerate reached higher production rates compared with the other two phases, suggesting that the pertraction system favored the oxidative pathway of glycerol fermentation. Valerate extraction reached a maximum of 30 g COD m−2 day−1. The filter microbiome was highly diverse with Simpson index values close to 0.1 for the four sludge samples collected, and a concomitant increase in Megasphaera elsdenii and an increase in valerate production rates were observed. Hence, high valerate production and extraction rates through the carboxylate platform are a feasible alternative for crude glycerol valorization with a great potential for improvement in future research.

Bioavailable electron donors from ultrasound-treated biomass for stimulating denitrification

Finding low-cost electron donors to drive denitrification is an important target for many municipal wastewater treatment plants (MWTPs). Excess sludge (biomass) potentially is a low-cost electron donor generated internally to the MWTP, but it has to be made more bioavailable. Aerobic and anoxic biomasses were treated with ultrasound, and their supernatants were used as electron donors for stimulating denitrification. The supernatant from ultrasound-treated anoxic biomass achieved 54% faster nitrate-N removal than did supernatant from the treated aerobic biomass, and the supernatant of untreated biomass was ineffective as an electron donor. UV illumination of the supernatants further enhanced the rates, with increments of 19% and 14%, respectively for the aerobic and anoxic supernatants. Sodium acetate at a range of initial concentrations was compared as a readily bioavailable electron donor to gauge the acceleration impact of the supernatants as equivalent bioavailable chemical oxygen demand (COD). The total chemical oxygen demand (TCOD) of the supernatant harvested from anoxic biomass without UV illumination was 76% bioavailable, while its bioavailable TCOD was 78% after UV illumination. For the supernatant from the aerobic biomass, the bioavailable fractions were, respectively, 56% and 58% without and with UV illumination. The greatest impact for converting excess biomass into a source of bioavailable electron donor to drive denitrification came from ultrasound treatment of the biomass, which disrupted the biomass to form particulate chemical oxygen demand (PCOD) that was bioavailable. PCOD was at least 51% bioavailable, and it contributed no less than 82% of the bioavailable COD.

Microaerophilic biodegradation of raw textile effluent by synergistic activity of bacterial community DR4

Treatment of raw textile effluent (RTE) is very difficult, due to its inherent heterogeneous, low-biodegradable and toxic compositions. Pure and mixed microbial cultures have limited metabolic capabilities in effective mineralization of complex RTE. Therefore, in this study a novel bacterial community DR4 was enriched directly into a complex RTE consisting of 27 different dyes using textile dye polluted soil as an inoculum. The rigorous enrichment process resulted in acclimatization of a taxonomically distinct bacterial population, with an abundance of the genus Comamonas in the bacterial community DR4 as compared to the abundance of Pseudomonas in the RTE respectively, as revealed by high-throughput 16S rRNA gene (V3–V4 region) sequencing. Microaerophilic treatment of RTE by enriched bacterial community DR4, in the presence of optimized electron donor (sucrose) and nitrogen source (yeast extract) resulted in 88% of American Dye Manufacturer's Institute (ADMI) removal and 98% of Chemical oxygen demand (COD) reduction within 32 h at 37 °C. In silico prediction of the functional genes within bacterial community DR4 was made by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis. The PICRUSt analysis revealed high abundance of xenobiotic degradation and metabolism genes. The predicted functional genes and textile dye degradation pathways were further validated using Ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared (FTIR) spectroscopy and High Resolution Liquid Chromatography coupled with Mass Spectrometry (HR-LCMS) based characterization of textile dye degradation metabolites. The activity of azoreductases in the cell-free extracts (CFE) of the enriched bacterial community DR4 was induced by 1.83–7.81 folds in the presence of representative textile dyes as compared to uninduced samples, which confirmed their role in textile effluent decolourization. The degradation of four representative azo dyes present in RTE such as Disperse orange 30, Reactive red 152, Direct blue 2 and Acid brown 15 depicted symmetric degradation of azo bonds by bacterial community DR4.

Photoredox Decarboxylative C(sp3)-N Coupling of α-Diazoacetates with Alkyl N-Hydroxyphthalimide Esters for Diversified Synthesis of Functionalized N-Alkyl Hydrazones.

Herein we report a metal-free photocatalytic coupling reaction for the synthesis of structurally and functionally diverse N-alkyl hydrazones from α-diazoacetates and N-alkyl hydroxyphthalimide esters. By employing Rose Bengal as a photocatalyst with yellow LEDs irradiation, over 60 N-alkyl hydrazones were synthesized. Fluorescence quenching analysis and deuterium incorporation experiments reveal that Hantzsch ester serves as both an electron donor and proton source for the reaction. This strategy offers a simple retrosynthetic disconnection for conventionally inaccessible C(sp3)-rich N-alkyl hydrazones.

Activated Carbon Mixed with Marine Sediment is Suitable as Bioanode Material for Spartina anglica Sediment/Plant Microbial Fuel Cell: Plant Growth, Electricity Generation, and Spatial Microbial Community Diversity

Wetlands cover a significant part of the world’s land surface area. Wetlands are permanently or temporarily inundated with water and rich in nutrients. Therefore, wetlands equipped with Plant-Microbial Fuel Cells (Plant-MFC) can provide a new source of electricity by converting organic matter with the help of electrochemically active bacteria. In addition, sediments provide a source of electron donors to generate electricity from available (organic) matters. Eight lab-wetlands systems in the shape of flat-plate Plant-MFC were constructed. Here, four wetland compositions with activated carbon and/or marine sediment functioning as anodes were investigated for their suitability as a bioanode in a Plant-MFC system. Results show that Spartina anglica grew in all of the plant-MFCs, although the growth was less fertile in the 100% activated carbon (AC100) Plant-MFC. Based on long-term performance (2 weeks) under 1000 ohm external load, the 33% activated carbon (AC33) Plant-MFC outperformed the other plant-MFCs in terms of current density (16.1 mA/m2 plant growth area) and power density (1.04 mW/m2 plant growth area). Results also show a high diversity of microbial communities dominated by Proteobacteria with 42.5–69.7% relative abundance. Principal Coordinates Analysis shows clear different bacterial communities between 100% marine sediment (MS100) Plant-MFC and AC33 Plant-MFC. This result indicates that the bacterial communities were affected by the anode composition. In addition, small worms (Annelida phylum) were found to live around the plant roots within the anode of the wetland with MS100. These findings show that the mixture of activated carbon and marine sediment are suitable material for bioanodes and could be useful for the application of Plant-MFC in a real wetland. Moreover, the usage of activated carbon could provide an additional function like wetland remediation or restoration, and even coastal protection.

Soluble Molybdenum Reduction by Morganella sp. Locally-isolated from Agricultural Land in Kano

Intensive agriculture and industrial activities have significantly increased the global burden of pollutants; thus, bioremediation of these pollutants is intensely sought. A bacterium with potential of reducing toxic soluble molybdenum to precipitable molybdenum blue (Mo-blue) was isolated from agricultural soil in Darmanawa, Kano state. The bacterium grown on low phosphate media (LPM) reduces molybadate to Mo-blue optimally at pH between 6.0 and 7.5, temperature of 35 °C, glucose was the best electron donor source at 5 g/L and ammonium sulphate was the best nitrogen source. The optimum molybdate concentration supporting the reduction process was 40 mM at 3.5 mM phosphate. Phylogenetic analysis of 16S rRNA partial sequence identified the bacterium as Morganella sp. The ability of this isolate to reduce toxic soluble molybdenum to colloidal less toxic form is novel and makes the bacterium an important instrument for bioremediation of this pollutant.

Isolation and Characterization of Molybdate-reducing Enterobacter cloacae from Agricultural Soil in Gwale LGA Kano State, Nigeria

Agricultural and industrial activities contribute most to the pollutants found globally; therefore, bioremediation of these pollutants is intensely sought. This research isolated a molybdenum-reducing bacterium from agricultural soil. The bacterium grown in low phosphate media (LPM) reduces molybadate to Mo-blue optimally at pH between 6.5 and 7.0, temperature between 35 and 40 °C, glucose at 5 g/L and glycine at 3 g/L were the best electron donor and nitrogen sources, respectively. The optimum molybdate concentration is between 80 and 100 mM, and phosphate concentration was between 5.0 and 7.5 mM. Phylogenetic analysis of 16S rRNA partial sequencing identified the bacterium as Enterobacter cloacae. The capacity of this bacterium to reduce toxic molybdenum to less toxic colloidal molybdenum blue is novel and form the basis for its use in future bioremediation of this pollutant.

Characterizing the Molybdenum-reducing Properties of Pseudomonas sp. locally isolated from Agricultural soil in Kano Metropolis Nigeria

Pollution of the environment by heavy metals and other toxic xenobiotics has increasingly become global public health concern. Bacterial reduction of molybdenum to insoluble molybdenum blue (Mo-blue) forms the basis for its bioremediation. A bacterium with the ability to reduce toxic soluble molybdenum has been isolated from Agricultural soil and identified as Pseudomonas sp. based on the 16S rRNA partial sequencing and phylogenetic analysis. Spectroscopic analysis reveals that the bacterium reduced sodium molybdate to Mo-blue optimally at pH between 6.5 and 7.0, temperatures between 35 °C and 40 °C. Glucose was the best electron donor source supporting molybdate reduction, followed by sucrose, fructose, glycerol and starch in descending order. Other requirements include a phosphate concentration of 3.5 mM and a molybdate concentration of between 40 and 60 mM. The absorption spectrum of the Mo-blue produced was similar to the previously isolated Mo-reducing bacteria and closely resembles a reduced phosphomolybdate.

Pantoea sp. strain HMY-P4 Reduced Toxic Hexavalent Molybdenum to Insoluble Molybdenum Blue

Bioremediation of pollutants such as heavy metals is an economic and environmentally friendly process. A novel molybdenum-reducing bacterium was isolated and characterized for its potential to reduce hexavalent molybdenum to molybdenum blue (Mo-blue). The bacterium reduces molybdate optimally at pH between 6 and 8, temperature between 35 and 40 ËšC. Glucose was the best electron donor source supporting molybdate reduction followed by sucrose, fructose, starch and glycerol in descending order. Other requirements include optimum phosphate concentration at 5.0 mM and molybdate concentration between 20 and 40 mM. 16S rRNA partial sequencing and phylogenetic analysis identified the bacterium as Pantoea sp. strain HMY-P4. The capacity of this bacterium to reduce toxic soluble molybdenum to a less toxic form is novel and makes the bacterium an important instrument for bioremediation of this pollutant. &#x0D;

Simultaneous nitrate and sulfide removal using a bio-electrochemical system

This study addresses the applicability of simultaneous nitrate and sulfide removal using two-chamber bio-electrochemical systems (BES). The anode and cathode chambers of a BES were fed with the effluent of a sulfate reducing reactor and a nitrate-rich groundwater as an electron donor and acceptor sources, respectively. BES has been found to be effective for simultaneous removal of sulfide and nitrate coming from different sources and without mixing them. As a result, 10 gS/m3/d of sulfide oxidation and 7.26 gN/m3/d of nitrate reduction rates were achieved. The number of electrons used for denitrification was more than that of delivered from the anode, especially when the anode chamber was fed with the SRR effluent and operated at pH 7–7.5. It was supposed that H2S was used for denitrification in the cathode by passing through the membrane. Another reason for this might be the electrons released from the corroding steel mesh current collector.

Microbial transformation of Se oxyanions in cultures of Delftia lacustris grown under aerobic conditions.

Delftia lacustris is reported for the first time as a selenate and selenite reducing bacterium, capable of tolerating and growing in the presence of ≥ 100 mM selenate and 25 mM selenite. The selenate reduction profiles of D. lacustris were investigated by varying selenate concentration, inoculum size, concentration and source of organic electron donor in minimal salt medium. Interestingly, the bacterium was able to reduce both selenate and selenite under aerobic conditions. Although considerable removal of selenate was observed at all concentrations investigated, D. lacustris was able to completely reduce 0.1 mM selenate within 96 h using lactate as the carbon source. Around 62.2% unaccounted selenium (unidentified organo-selenium compounds), 10.9% elemental selenium and 26.9% selenite were determined in the medium after complete reduction of selenate. Studies of the enzymatic activity of the cell fractions show that the selenite/selenate reducing enzymes were intracellular and independent of NADPH availability. D. lacustris shows an unique metabolism of selenium oxyanions to form elemental selenium and possibly also selenium ester compounds, thus a potential candidate for the remediation of selenium-contaminated wastewaters in aerobic environments. This novel finding will advance the field of bioremediation of selenium-contaminated sites and selenium bio-recovery and the production of potentially beneficial organic and inorganic reactive selenium species.