Shewanella Decolorationis Research Articles

Bio-Electro-Fenton Process Driven by Microbial Fuel Cell for Wastewater Treatment

In this study, we proposed a new concept of utilizing the biological electrons produced from a microbial fuel cell (MFC) to power an E-Fenton process to treat wastewater at neutral pH as a bioelectro-Fenton (Bio-E-Fenton) process. This process can be achieved in a dual-chamber MFC from which electrons were generated via the catalyzation of Shewanella decolorationis S12 in its anaerobic anode chamber and transferred to its aerated cathode chamber equipped with a carbon nanotube (CNT)/gamma-FeOOH composite cathode. In the cathode chamber, the Fenton's reagents including hydrogen peroxide (H(2)O(2)) and ferrous irons (Fe(2+)) were in situ generated. This Bio-E-Fenton process led to the complete decolorization and mineralization of Orange II at pH 7.0 with the apparent first-order rate constants, k(app) = 0.212 h(-1) and k(TOC) = 0.0827 h(-1), respectively, and simultaneously produced a maximum power output of 230 mW m(-2) (normalized to the cathode surface area). The apparent mineralization current efficiency was calculated to be as high as 89%. The cathode composition was an important factor in governing system performance. When the ratio of CNT to gamma-FeOOH in the composite cathode was 1:1, the system demonstrated the fastest rate of Orange II degradation, corresponding to the highest amount of H(2)O(2) formed.

Enhanced reductive dechlorination of DDT in an anaerobic system of dissimilatory iron-reducing bacteria and iron oxide

The transformation of DDT was studied in an anaerobic system of dissimilatory iron-reducing bacteria ( Shewanella decolorationis S12) and iron oxide (α-FeOOH). The results showed that S. decolorationis could reduce DDT into DDD, and DDT transformation rate was accelerated by the presence of α-FeOOH. DDD was observed as the primary transformation product, which was demonstrated to be transformed in the abiotic system of Fe 2+ + α-FeOOH and the system of DIRB + α-FeOOH. The intermediates of DDMS and DBP were detected after 9 months, likely suggesting that reductive dechlorination was the main dechlorination pathway of DDT in the iron-reducing system. The enhanced reductive dechlorination of DDT was mainly due to biogenic Fe(II) sorbed on the surface of α-FeOOH, which can serve as a mediator for the transformation of DDT. This study demonstrated the important role of DIRB and iron oxide on DDT and DDD transformation under anaerobic iron-reducing environments.

Partial degradation mechanisms of malachite green and methyl violet B by Shewanella decolorationis NTOU1 under anaerobic conditions

This work demonstrated that Shewanella decolorationis NTOU1 decolorized 200 mg l −1 of crystal violet, malachite green, or methyl violet B within 2–11 h under anaerobic conditions at 35 °C. The initial color removal rate of malachite green was highest, while that of methyl violet was lowest. GC/MS analyses of the intermediate compounds produced during and after decolorization of malachite green and methyl violet B suggested that biodegradation of these dyes involved reduction to leuco form, N-demethylation, and reductive splitting of the triphenyl rings. The number of N-methylated groups of these dyes might have influenced decolorization rates and the reductive splitting of the triphenyl rings of these dyes. Cytotoxicity and antimicrobial test data showed that malachite green and methyl violet B solution (100 mg l −1) were toxic. Toxicity of the dyes decreased after their decolorization, but further incubation resulted in increased toxicity.

Two different electron transfer pathways may involve in azoreduction in Shewanella decolorationis S12

Electron transfer pathways for azoreduction by S. decolorationis S12 were studied using a mutant S12-22 which had a transposon insertion in ccmA. The results imply that there are two different pathways for electron transport to azo bonds. The colony of S12-22 was whitish and incapable of producing mature c-type cytochromes whose alpha-peak was at 553 nm in the wild type S12. The mutant S12-22 could not use formate as the sole electron donor for azoreduction either in vivo or in vitro, but intact cells of S12-22 were able to reduce azo dyes of low polarity, such as methyl red, when NADH was served as the sole electron donor. Although the highly polar-sulfonated amaranth could not be reduced by intact cells of S12-22, it could be efficiently reduced by cell extracts of the mutant when NADH was provided as the sole electron donor. These results suggest that the mature c-type cytochromes are essential electron mediators for the extracellular azoreduction of intact cells, while the other pathway without the involvement of mature c-type cytochromes, NADH-dependent oxidoreductase-mediated electron transfer pathway can reduce lowly polar sulfonated azo dyes inside the whole cells or highly polar sulfonated azo dyes in the cell extracts without bacterial membrane barriers.

A polypyrrole/anthraquinone-2,6-disulphonic disodium salt (PPy/AQDS)-modified anode to improve performance of microbial fuel cells

This study reports a new approach of improving performance of microbial fuel cells (MFCs) by using a polypyrrole/anthraquinone-2,6-disulphonic disodium salt (PPy/AQDS)-modified anode. The immobilization of AQDS on a carbon felt anode was accomplished by electropolymerization of pyrrole while using AQDS as the dopant. The dual-chamber MFC operated with this modified anode in the presence of Shewanella decolorationis S12 showed the maximum power density of 1303 mW m −2, which was 13 times larger than that obtained from the MFC equipped with an unmodified anode. Evidence from cyclic voltammerty (CV) and scanning electron microscopy (SEM) results indicated that the increase in power generation was assigned to the increased surface area of anode, the enhanced electron-transfer efficiency from the bacteria to the anode via immobilized AQDS, and an increase in the number of bacteria attached to anode.

Interactively interfacial reaction of iron-reducing bacterium and goethite for reductive dechlorination of chlorinated organic compounds

The interactively interfacial reactions between the iron-reducing bacterium (Shewanella decolorationis, S12) and iron oxide (α-FeOOH) were investigated to determine reductive dechlorination transformation of chlorinated organic compounds (chloroform and pentachlorophenol). The results showed that the interactive system of S12+ α-FeOOH exhibited relatively high dechlorination rate. By comparison, the S12 biotic system alone had no obvious dechlorination, and the α-FeOOH abiotic system showed low dechlorination rate. The enhanced dechlorination of chloroform and pentachlorophenol in the interactive system of S12+α-FeOOH was derived from the promoted generation of adsorbed Fe(II) by S12. A decrease in redox potential of the Fe(III)/Fe(II) couple in the interactive reaction system was determined by cyclic voltammetry. Our results will give new insight into interactively interfacial reaction between iron-reducing bacterium and iron oxides for degradation of chlorinated organic compounds under anaerobic condition.

Effects of Oxytetracycline and Sulfachloropyridazine Residues on the Reductive Activity of Shewanella decolorationis S12

Effects of oxytetracycline (OTC) and sulfachloropyridazine (SCP), two of the widely used antibiotics in livestock production, on beneficial environmental microorganisms were studied. Shewanella decolorationis S12 was selected as the target bacteria for the role in reduction of Fe(III) and dye under anaerobic conditions. The results showed that the antibiotics significantly inhibited Fe(III) reduction and dye decoloration in the reduction system. The rates of Fe(II) formed (-r) were 3.6 and 0.2 mg/L/day for the OTC concentrations of 0-1 mg/L and 1-50 mg/L, respectively, with 1 mg/L as the turning point of the inhibition effect. The turning point of inhibition effect was much higher for SCP treatments, at 4 mg/L. The results also showed higher production values for adsorbed Fe(II) than soluble Fe(II) in OTC treatments, but the reverse occurred in the SCP treatments. The difference between the treatments could be due to higher sorption coefficients of OTC as compared to SCP. Transmission electron micrographs showed changes in cell structures of S. decolorationis S12 grown in medium with OTC. Detached cell walls and large vacuoles in internal cell contents were found in OTC-treated cells. The results of the present study indicated that the inhibition of antibiotic on the reduction activity of S. decolorationis S12 may be due to a decrease in live S. decolorationis S12 population and/or damages of their cell structure in this reduction system.

Energy Generation Coupled to Azoreduction by Membranous Vesicles from Shewanella decolorationis S12

Previous studies have demonstrated that Shewanella decolorationis S12 can grow on the azo compound amaranth as the sole electron acceptor. Thus, to explore the mechanism of energy generation in this metabolism, membranous vesicles (MVs) were prepared and the mechanism of energy generation investigated. The membrane, which was fragmentized during preparation, automatically formed vesicles ranging from 37.5-112.5 nm in diameter under electron micrograph observation. Energy was conserved when coupling the azoreduction by the MVs of an azo compound or Fe(III) as the sole electron acceptor with H2, formate, or lactate as the electron donor. The amaranth reduction by the vesicles was found to be inhibited by specific respiratory inhibitors, including Cu(2+) ions, dicumarol, stigmatellin, and metyrapone, indicating that the azoreduction was indeed a respiration reaction. This finding was further confirmed by the fact that the ATP synthesis was repressed by the ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD). Therefore, this study offers solid evidence of a mechanism of microbial dissimilatory azoreduction on a subcell level.

Identification of an uptake hydrogenase for hydrogen-dependent dissimilatory azoreduction by Shewanella decolorationis S12

Shewanella decolorationis S12, a representative dissimilatory azo-reducing bacterium of Shewanella genus, can grow by coupling the oxidation of hydrogen to the reduction of azo compounds as the sole electron acceptor, indicating that an uptake hydrogenase is an important component for electron transfer for azoreduction. For searching to the uptake hydrogenase in the genome of S. decolorationis, two operons, hyd and hya, were cloned and sequenced, which encode periplasmically oriented Fe-only hydrogenase and a Ni-Fe hydrogenase, respectively, according to the homologous comparison with other bacterial hydrogenases. In order to assess the roles of these two enzymes in hydrogen-dependent azoreduction and growth, hyd- and hya-deficient mutants were generated by gene replacement. Hya was found to be required for hydrogen-dependent reduction of azo compound by resting cell suspensions and to be essential for growth with hydrogen as electron donor and azo compound as electron acceptor. Hyd, in contrast, was not. These findings suggest that Hya is an essential respiratory hydrogenase of dissimilatory azoreduction in S. decolorationis.

Biodegradation of crystal violet by a Shewanella sp. NTOU1

A bacterial isolate, strain NTOU1, originally isolated from the cooling system in an oil refinery could decolorize and detoxify crystal violet under anaerobic conditions. The strain was characterized and identified as a member of Shewanella decolorationis based on Gram staining, morphology characters, biochemical tests, the 16S rRNA gene and the gyrase subunit beta gene ( gyrB). The optimum pH value and temperature for decolorization of crystal violet by this strain under anaerobic conditions were pH 8–9 and 30–40 °C, respectively. Formate (20 mM) was the best electron donor. Addition of ferric citrate did not inhibit decolorization of crystal violet, the addition of thiosulfate, ferric oxide, or manganese oxide slightly decreased decolorization, while addition of nitrite (20 mM) inhibited the decolorization of crystal violet. By supplementing the medium with formate and ferric citrate and cultivating it under optimum pH and temperature, this strain could remove crystal violet, at a concentration of 1500 mg l −1, at the rate of 298 mg l −1 h −1 (during decolorization the OD 600 of the cell culture increased from ∼0.6 to ∼1.2). GC/MS analysis of the degradation products of crystal violet detected the presence of N, N′-bis(dimethylamino) benzophenone (Michler’s Ketone), [ N, N-dimethylaminophenyl] [ N-methylaminophenyl] benzophenone, N, N-dimethylaminobenzaldehyde, N, N-dimethylaminophenol, and 4-methylaminophenol. These results suggest that crystal violet was biotransformed into N, N-dimethylaminophenol and Michler’s Ketone prior to further degradation of these intermediates. This paper proposes a probable pathway for the degradation of crystal violet by this Shewanella sp. Cytotoxicity and antimicrobial tests showed that the process of decolorization also detoxify crystal violet.

Respiration and Growth of Shewanella decolorationis S12 with an Azo Compound as the Sole Electron Acceptor

Respiration and Growth of <i>Shewanella decolorationis</i> S12 with an Azo Compound as the Sole Electron Acceptor

Biodegradation of textile azo dye by Shewanella decolorationis S12 under microaerophilic conditions

The complete biodegradation of azo dye, Fast Acid Red GR, was observed under microaerophilic conditions by Shewanella decolorationis S12. Although the highest decolorizing rate was measured under anaerobic condition and the highest biomass was obtained under aerobic condition, a further biodegradation of decolorizing products can only be achieved under microaerophilic conditions. Under microaerophilic conditions, S. decolorationis S12 could use a range of carbon sources for azo dye decolorization, including lactate, formate, glucose and sucrose, with lactate being the optimal carbon source. Sulfonated aromatic amines were not detected during the biotransformation of Fast Acid Red GR, while H(2)S formed. The decolorizing products, aniline, 1,4-diaminobenzene and 1-amino-2-naphthol, were followed by complete biodegradation through catechol and 4-aminobenzoic acid based on the analysis results of GC-MS and HPLC.

Fe(III)-enhanced Azo Reduction by Shewanella decolorationis S12

Shewanella decolorationis S12 is capable of high rates of azo dye decolorization and dissimilatory Fe(III) reduction. Under anaerobic conditions, when Fe(III) and azo dye were copresent in S12 cultures, dissimilatory Fe(III) reduction and azo dye biodecolorization occurred simultaneously. Furthermore, the dye decolorization was enhanced by the presence of Fe(III). When 1 mM Fe(III) was added, the methyl red decolorizing efficiency was 72.1% after cultivation for 3 h, whereas the decolorizing efficiency was only 60.5% in Fe(III)-free medium. The decolorizing efficiencies increased as the concentration of Fe(III) was increased from 0 to 6 mM. Enzyme activities, which mediate the dye decolorization and Fe(III) reduction, were not affected by preadaption of cells to Fe(III) and azo dye nor by the addition of chloramphenicol. Both the Fe(III) reductase and the azo reductase were membrane associated. The respiratory electron transport chain inhibitors metyrapone, dicumarol, and stigmatellin showed significantly different effects on Fe(III) reduction than on azo dye decolorization.

Effects of electron donors and acceptors on anaerobic reduction of azo dyes by Shewanella decolorationis S12

Shewanella decolorationis S12 was able to reduce various azo dyes in a defined medium with formate, lactate, and pyruvate or H(2) as electron donors under anaerobic conditions. Purified membranous, periplasmic, and cytoplasmic fractions from strain S12 analyzed, respectively, only membranous fraction was capable of reducing azo dye in the presence of electron donor, indicating that the enzyme system for anaerobic azoreduction was located on cellular membrane. Respiratory inhibitor Cu(2+), dicumarol, stigmatellin, and metyrapone inhibited anaerobic azoreduction by purified membrane fraction, suggesting that the bacterial anaerobic azoreduction by strain S12 was a biochemical process that oxidizes the electron donors and transfers the electrons to the acceptors through a multicompound system related to electron transport chain. Dehydrogenases, cytochromes, and menaquinones were essential electron transport components for the azoreduction. The electron transport process for azoreduction was almost fully inhibited by O(2), 6 mM of NO3-, and 0.9 mM of NO2-, but not by 10 mM of Fe(3+). The inhibition may be a result from the competition for electrons from electron donors. These findings impact on the understanding of the mechanism of bacterial anaerobic azoreduction and have implication for improving treatment methods of wastewater contaminated by azo dyes.

Reduction and partial degradation mechanisms of naphthylaminesulfonic azo dye amaranth by Shewanella decolorationis S12

Reduction and biodegradation mechanisms of naphthylaminesulfonic azo dye amaranth using a newly isolated Shewanella decolorationis strain S12 were investigated. Under anaerobic conditions, amaranth was reduced by strain S12, and a stoichiometric amount of two reduction products RP-1 and RP-2 were generated. UV/visible spectrophotometric and high performance liquid chromatography (HPLC) analysis indicated that RP-1 and RP-2 were 1-aminenaphthylene -4-sulfonic acid and 1-aminenaphthylene-2-hydroxy-3, 6-disulfonic acid. The result strongly supports a mechanism of azo dye reduction by the process via the reductive cleavage of the azo bond to form corresponding aromatic amines. The result of HPLC analyses revealed that these aromatic amines were not able to be mineralized by strain S12 under anaerobic conditions. But after re-aeration of the decolorized culture, RP-2 was mineralized completely by this microorganism, but the consumption of RP-1 was not observed. Ames test showed that amaranth had mutagenic but no cytotoxic potential. The mutagenic potential was relieved after the anaerobic treatment with strain S12 as the mutagenic effect of the two reduction products from amaranth was not detected by Ames test. Thus, the ability of strain S12 to reduce and partially mineralize the naphthylaminesulfonic azo dye efficiently was demonstrated, which can potentially be used to biodegrade and detoxify wastewater containing azo dyes using an alternating anaerobic/aerobic treatment procedure.

Shewanella spongiae sp. nov., isolated from a marine sponge

A psychrophilic bacterium, designated strain HJ039(T), was isolated from a marine sponge collected in the East Sea of Korea (also known as the Sea of Japan). Cells were Gram-negative, motile and rod-shaped (1.8-3.54 microm x 0.27-0.73 microm). Growth was observed between 5 and 26 degrees C (optimum 15 degrees C), at pH 5.0-8.5 (optimum pH 6.0-6.5) and in the presence of 0-6.0 % NaCl (optimum 2.0 %). The 16S rRNA gene sequence of strain HJ039(T) showed high levels of similarity (93.7-95.4 %) with members of the genus Shewanella, especially with Shewanella gaetbuli TF-27(T) (95.2 %), Shewanella decolorationis S12(T) (94.9 %), Shewanella putrefaciens LMG 26268(T) (94.6 %), Shewanella hafniensis P010(T) (94.6 %), Shewanella algae ATCC 51192(T) (94.5 %) and Shewanella kaireitica c931(T) (94.5 %). However, phylogenetic analysis revealed that strain HJ039(T) shared a phyletic line with S. algae and Shewanella amazonensis. The major respiratory quinone was Q-8. The DNA G+C content was 52.8 mol%. The major fatty acids were i-13 : 0 (8.5 %), 15 : 0 (4.2 %), i-15 : 0 (23.2 %), i-15 : 1 (7.9 %), 16 : 0 (8.7 %), 16 : 1omega7 (21.0 %) and 17 : 1omega8 (6.4 %). From this polyphasic taxonomic evidence, strain HJ039(T) is considered to represent a novel species of the genus Shewanella, for which the name Shewanella spongiae sp. nov. is proposed. The type strain is HJ039(T) (=KCCM 42304(T)=JCM 13830(T)).

Respiration and Growth of Shewanella decolorationis S12 with an Azo Compound as the Sole Electron Acceptor

The ability of Shewanella decolorationis S12 to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory azoreduction was investigated. This microorganism can reduce a variety of azo dyes by use of formate, lactate, pyruvate, or H(2) as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0 x 10(7) cells per ml after compete reduction of 2.0 mM amaranth in a defined medium. This was accompanied by a stoichiometric consumption of 4.0 mM formate over time when amaranth and formate were supplied as the sole electron acceptor and donor, respectively, suggesting that microbial azoreduction is an electron transport process and that this electron transport can yield energy to support growth. Purified membranous, periplasmic, and cytoplasmic fractions from S12 were analyzed, but only the membranous fraction was capable of reducing azo dyes with formate, lactate, pyruvate, or H(2) as the electron donor. The presence of 5 microM Cu(2+) ions, 200 microM dicumarol, 100 microM stigmatellin, and 100 microM metyrapone inhibited anaerobic azoreduction activity by both whole cells and the purified membrane fraction, showing that dehydrogenases, cytochromes, and menaquinone are essential electron transfer components for azoreduction. These results provide evidence that the microbial anaerobic azoreduction is linked to the electron transport chain and suggest that the dissimilatory azoreduction is a form of microbial anaerobic respiration. These findings not only expand the number of potential electron acceptors known for microbial energy conservation but also elucidate the mechanisms of microbial anaerobic azoreduction.

Decolorization of anthraquinone dye by Shewanella decolorationis S12

A new species of genus Shewanella, Shewanella decolorationis S12, from activated sludge of a textile-printing wastewater treatment plant, can decolorize Reactive Brilliant Blue K-GR, one kind of anthraquinone dye, with flocculation first. Although S. decolorationis displayed good growth in an aerobic condition, color removal was the best in an anaerobic condition. For color removal, the most suitable pH values and temperatures were pH 6.0-8.0 and 30-37 degrees C under anaerobic culture. More than 99% of Reactive Brilliant Blue K-GR was removed in color within 15 h at a dye concentration of 50 mg/l. Lactate was the suitable carbon source for the dye decolorization. A metal compound, HgCl(2), had the inhibitory effect on decolorization of Reactive Brilliant Blue K-GR, but a nearly complete decolorization also could be observed at a HgCl(2) concentration of 10 mg/l. The enzyme activities, which mediate the tested dye decolorization, were not significantly affected by preadaptation of the bacterium to the dye.

Shewanella decolorationis sp. nov., a dye-decolorizing bacterium isolated from activated sludge of a waste-water treatment plant

A highly efficient dye-decolorizing bacterium, strain S12T, was isolated from activated sludge of a textile-printing waste-water treatment plant in Guangzhou, China. The cells were Gram-negative and motile by means of a single polar flagellum. The strain was capable of anaerobic growth either by fermentation of glucose or by anaerobic respiration and utilized a variety of electron acceptors, including nitrate, iron oxide and thiosulfate. The physiological properties, tested by using the Biolog GN2 system, were similar to those of the genus of Shewanella. Analysis of the nearly complete 16S rRNA gene sequence of strain S12T showed the highest similarity (98 and 97 %, respectively) to Shewanella baltica and Shewanella putrefaciens. However, the level of gyrB similarity between strain S12T and S. putrefaciens was 87 %. DNA from strain S12T showed 41.8 and 41.9 % DNA relatedness, respectively, to the DNA of S. baltica DSM 9439T and S. putrefaciens DSM 6067T. The DNA G+C content of strain S12T was 49.3 mol%. The predominant menaquinone was MK-7 and the predominant ubiquinones were Q-7 and Q-8. The dominant fatty acids were 15 : 0, 16 : 0, iso-15 : 0 and 16 : 1omega7c, similar to the profiles of other Shewanella species. On the basis of its physiological and molecular properties, strain S12T appears to represent a novel species of the genus Shewanella, for which the name Shewanella decolorationis sp. nov. is proposed. The type strain is S12T (=CCTCC M 203093T=IAM 15094T).