Shewanella Decolorationis S12 Research Articles

Characterizing the snorkeling respiration and growth of Shewanella decolorationis S12

Microbial electrochemical snorkel (MES) reactor is a simplified bioreactor based on microbial fuel cells (MFCs) and has been suggested to be a promising approach to solve many environmental problems. However, the microbial processes in MES reactors have not yet been characterized. This study shows that Shewanella decolorationis S12 can use the conductive snorkel as direct electron acceptor for respiration and growth. Similar with current-generating biofilms, cellular viability in MES biofilms decreased with the distance from snorkel. MES reactors showed more rapid cell growth and substrate consumption than MFCs. Although the biomass density of MES biofilm was higher than that of anode biofilms, the current-generating capacity and electrochemical activity of MES biofilm were lower, which could be attributed to the lower cytochrome c expression in MES biofilm caused by the higher redox potential of MES. These microbiological and electrochemical properties are essential for the further development of MES reactors.

Shewanella seohaensis sp. nov., isolated from a tidal flat sediment

A Gram-negative, motile and rod-shaped bacterial strain, designated S7-3(T), was isolated from a tidal flat sediment at Saemankum on the western coast of Korea. Phylogenetic analyses based on 16S rRNA gene and gyrB sequences showed that strain S7-3(T) belonged to the genus Shewanella, clustering with Shewanella decolorationis S12(T). Strain S7-3(T) exhibited 98.8 % 16S rRNA gene sequence similarity and 96.8 % gyrB sequence similarity to S. decolorationis S12(T), respectively. The 16S rRNA gene sequence similarity values between strain S7-3(T) and other members of the genus Shewanella were in the range of 93.0-98.0 %. Strain S7-3(T) contained simultaneously both menaquinones (MK) and ubiquinones (Q); the predominant menaquinone was MK-7 and the predominant ubiquinones were Q-7 and Q-8. The fatty acid profiles of strain S7-3(T) and S. decolorationis JCM 21555(T) were similar; major components were C(17:1) ω8c, iso-C(15:0) and iso-C(15:0) 2-OH and/or C(16:1) ω7c. The DNA G+C content of strain S7-3(T) was 51.8mol% and its mean DNA-DNA relatedness value with S. decolorationis JCM 21555(T) was 43 %. Differential phenotypic properties of strain S7-3(T), together with the phylogenetic and genetic distinctiveness, revealed that this strain is distinguishable from recognized Shewanella species. On the basis of the data presented, strain S7-3(T) is considered to represent a novel Shewanella species, for which the name Shewanella seohaensis sp. nov. is proposed. The type strain is S7-3(T) (=KCTC 23556(T)=CCUG 60900(T)).

Reduction of structural Fe(III) in oxyhydroxides by Shewanella decolorationis S12 and characterization of the surface properties of iron minerals

Purpose Dissimilatory iron reduction is an important iron biogeochemical process in subsurface soils. Many researchers have studied the effects of various factors on this process. However, this process in the natural environment is complicated; thus, all the factors should be investigated systematically and simultaneously. The aims of this study were to investigate the effects of Fe(III) availability, surface areas, and crystallinity on Fe(III) reduction in different buffers and to characterize the surface properties of iron minerals. Materials and methods Microbial reductions of four chemically synthesized iron(III) oxyhydroxides [i.e., hydrous ferric oxide (HFO), α-FeOOH, γ-FeOOH, and α-Fe2O3] were conducted in batch cultures inoculated with an ironreducing bacterium, Shewanella decolorationis S12, in

Differential biofilms characteristics of Shewanella decolorationis microbial fuel cells under open and closed circuit conditions

Biofilms formation capacities of Shewanella species in microbial fuel cells (MFCs) and their roles in current generation have been documented to be species-dependent. Understandings of the biofilms growth and metabolism are essential to optimize the current generation of MFCs. Shewanella decolorationis S12 was used in both closed-circuit and open-circuit MFCs in this study. The anodic S. decolorationis S12 biofilms could generate fivefold more current than the planktonic cells, playing a dominant role in current generation. Anodic biofilms viability was sustained at 98±1.2% in closed-circuit while biofilms viability in open-circuit decreased to 72±7% within 96h. The unviable domain in open-circuit MFCs biofilms majorly located at the inner layer of biofilm. The decreased biofilms viability in open-circuit MFCs could be recovered by switching into closed-circuit, indicating that the current-generating anode in MFCs could serve as a favorable electron acceptor and provide sufficient energy to support cell growth and metabolism inside biofilms.

Role of iron in azoreduction by resting cells of Shewanella decolorationis S12

To investigate the role of soluble and insoluble iron in azoreduction by resting cells of Shewanella decolorationis S12. A series of analytical experiments were carried out. Results showed that insoluble Fe(2) O(3) all delayed the reduction of amaranth but did not inhibit it. Adsorption to Fe(2) O(3) particles by the bacterial cell surface could be the reason leading to the delay in azoreduction. For the soluble iron, an important finding was that azoreduction activities were inhibited by soluble iron in high concentration because of its higher redox potential, and the inhibition was strengthened when the electron donor supply was insufficient. However, activities of azoreduction could be enhanced by low concentration of soluble iron. This stimulating effect was because of the electron transfer but not the cell growth. The effects of iron on azoreduction by the resting cells depended on the solubility and concentration of the iron compounds, which was different from what was observed by the growing cells in the previous studies. This study has both theoretical significance in the microbial physiology and practical significance in the bioremediation of azo dyes-contaminated environment.

Extracellular respiration of different amounts azo dye by Shewanella decolorationis S12 and comparative analysis of the membrane proteome

Shewanella decolorationis S12 is capable of using azo compounds as terminal electron acceptors for respiration. However, knowledge about membrane proteins involved in this biochemical process is still limited. In addition, little is known about cell growth of this species in response to the increasing level of azo dye. In the present study, different culture methods were used to compare the biomass production rates of strain S12 in the presence of a high polarity azo dye, amaranth, as the sole terminal electron acceptor. The use of a fed-batch fermentor culture method allowed a much higher biomass accumulation in the presence of higher amounts of amaranth, compared to static serum bottle culture. Membrane proteome profiles were obtained by two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF/MS) for cells grown with different amounts of amaranth under anaerobic conditions. Three proteins Ndk, ClpP, and ArgC were found in markedly increased abundance in response to the growth increases in the presence of amaranth. Bioinformatics analysis implicated that these three proteins may be involved in azo respiration and energy conservation in strain S12. These findings provide valuable information for better understanding the extracellular azo respiration of S. decolorationis S12.

Comparative analysis of membranous proteomics of Shewanella decolorationis S12 grown with azo compound or Fe (III) citrate as sole terminal electron acceptor

Shewanella decolorationis S12 is capable of carrying out anaerobic respiration using azo dyes and Fe (III) citrate as electron acceptors. In the present study, proteomic techniques including two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry were used to analyze the similarity and the dissimilarity of the membrane proteins isolated from strain S12 cells grown in amaranth or Fe (III) citrate with defined inorganic salt medium. The cells of strain S12 grown under a saturated dissolved oxygen condition served as controls. This is the first work that made the comparative analysis of cell membranous proteomics of strain S12 grown with azo compound or Fe (III) citrate as a sole terminal electron acceptor. The results showed that most of the membrane proteins of strain S12 under azo respiration are similar to those under Fe (III) respiration, but dissimilar from those of oxygen-grown cells. FdnH and FrdB were expressed specifically in azo respiration. NqrA-2, DctP, and hypothetical protein SO_4719 showed relative overexpression in azo respiration compared with Fe (III) respiration. OmpA family protein SO_3545 was detected to be specific to Fe (III) respiration. Furthermore, ArgF, SdhA, and HoxK were expressed markedly in both amaranth- and Fe (III) citrate-grown cultures compared with oxygen-grown cultures.

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.

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.

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 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.

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.