Characterization of the differentiated reduction of selenite and tellurite by a halotolerant bacterium: Process and mechanism

Se(IV)-and Te(IV)-containing wastewater usually contains salt, which reduces the activity of conventional mi-croorganisms and may affect their microbial treatment. So far, salt-tolerant Se(IV)-and Te(IV)-reducing bacteria are very limited. Moreover, the detailed molecular response of microbial reduction of Se(IV)/Te(IV) under saline conditions has yet to be reported. In this study, the Se(IV) and Te(IV) reductive processes and mechanisms were investigated with the employment of a marine bacterium Shewanella sp. CNZ-1 (CNZ-1) using process and kinetic analyses, enzymology and RT-qPCR analyses, and differential proteomics approaches. Our results showed that CNZ-1 can effectively reduce Se(IV) and Te(IV) to Se0 and Te0 with the max k (R2) values of 0.0412 h-1 (0.86) and 0.0292 h(-1) (0.91) under 2% NaCl conditions, respectively. The mechanism study showed that CNZ-1 mediated Se(IV) reduction was an enzyme-based reductive reaction, whereas CNZ-1 mediated Te(IV) reduc-tion was more like a resistance-related detoxification process (including both bioadsorption and bioreduction). The bioreduction of Se(IV) was mainly depended on functional membrane proteins (> 4-fold; e.g., nitrite reductase, polysulfide reductase and fumarate reductase), while proteins related to efflux system and stress resistance system (> 2-fold; e.g., Type II secretory pathway and phage shock proteins) were essential for the Te (IV) bioreduction process. Overall, our findings expanded the understanding the fate of Se(IV) and Te(IV) in the saline environment and provided guidance for Se(IV) or Te(IV) pollution control

How iron-bearing minerals affect the biological reduction of Sb(V): A newly discovered function of nitrate reductase

As a toxic element of global concern, the elevated concentration of antimony (Sb) in the environment has attracted increasing attention. Microorganisms have been reported as important driving forces for Sb transformation. Iron (Fe) is the most important metal associated element of Sb, however, how Fe-bearing minerals affect the biological transformation of Sb is still unclear. In this study, the effects of Fe-bearing minerals on biological Sb(V) reduction were investigated by employing a marine Shewanella sp. CNZ-1 (CNZ-1). Our results showed that the presence of hematite, magnetite and ferrihydrite (1 g/L) resulted in a decrease in Sb(III) concentration of similar to 19-31 % compared to the Fe(III)-minerals free system. The calculated Sb(V) reduction rates are 0.0256 (R-2 0.71), 0.0389 (R-2 0.87), 0.0299 (R-2 0.96) and 0.0428 (R-2 0.95) h(-1) in the hematite-, magnetite-, ferrihydrite-supplemented and Fe(III)-minerals free systems, respectively. The cube-shaped Sb2O3 was characterized as a reductive product by using XRD, XPS, FTIR, TG and SEM approaches. Differential proteomic analysis showed that flagellar protein, cytochrome c, electron transfer flavoprotein, nitrate reductase and polysulfide reductase (up-regulation >1.5-fold, p value <0.05) were supposed to be included in the electron transport pathway of Sb(V) reduction by strain CNZ-1, and the key role of nitrate reductases was further highlighted during this reaction process based on the RT-qPCR and confirmatory experiments. Overall, these findings are beneficial to understand the environmental fate of Sb in the presence of Fe-bearing minerals and provide guidance in developing the bacteria/enzyme-mediated control strategy for Sb pollution

Degradation of Ethylbenzene in Aqueous Solution by Sodium Percarbonate Activated with EDDS–Fe(III) Complex

Ethylbenzene (EB) degradation performance in (S,S)-ethylenediamine-N,N-disuccinic acid (EDDS) chelated Fe(III) activated sodium percarbonate (SPC) system was investigated in this study. The effects of various factors, such as the dosages of SPC and Fe(III), molar ratio of EDDS/Fe(III), anions (Cl−, HCO3−, SO42−, and NO3−) concentration, natural organic matters (NOM), and initial solution pH were evaluated. The results showed that the addition of EDDS remarkably improved the EB removal in Fe(III)/SPC system. Both HCO3− anions and NOM had significantly inhibitive effect, while the influence of SO42−, Cl− and NO3− could be negligible on EB degradation. The EB removal was inhibited at extremely low and high initial solution pH. Moreover, the results of free radical probe tests, scavenger tests and electron paramagnetic resonance (EPR) detection indicated that OH was the predominant species responsible for EB degradation even though both OH and O2− were generated in the SPC/EDDS–Fe(III) system. The oxidation products were analyzed and possible EB degradation pathways were proposed. In conclusion, this study provides an important insight into the application of SPC/EDDS–Fe(III) system in the removal of EB contaminant, especially for in situ remediation of BTEX-contaminated groundwater

Enhanced Degradation of Trichloroethene by Sodium Percarbonate Activated with Fe (II) in the Presence of Citric Acid

Trichloroethene (TCE) degradation by Fe(II)-activated sodium percarbonate (SPC) in the presence of citric acid (CA) in aqueous solution was investigated. The results indicated that the presence of CA enhanced TCE degradation significantly by promoting HO• generation. The presence of Cl−, HCO3− and the initial solution pH appeared to be not negligible on the effect of TCE oxidation, while humic acid had no influence on TCE degradation. The generation of HO• and O2−• in the SPC/Fe(II)/CA system was confirmed with chemical probes, and the radical scavenging tests showed that TCE degradation was due to direct oxidation by HO•. Acidic pH condition was favorable for TCE degradation. In summary, this study provided detailed information for the application of the CA-enhanced Fe(II)-activated SPC technique for TCE-contaminated groundwater remediation

Benzene Oxidation by Fe(III)-Activated Percarbonate: Matrix-Constituent Effects and Degradation Pathways

Complete degradation of benzene by the Fe(III)-activated sodium percarbonate (SPC) system is demonstrated. Removal of benzene at 1.0 mM was seen within 160 min, depending on the molar ratios of SPC to Fe(III). A mechanism of benzene degradation was elaborated by free-radical probe-compound tests, free-radical scavengers tests, electron paramagnetic resonance (EPR) analysis, and determination of Fe(II) and H2O2 concentrations. The degradation products were also identified using gas chromatography-mass spectrometry method. The hydroxyl radical (HO) was the leading species in charge of benzene degradation. The formation of HO was strongly dependent on the generation of the organic compound radical (R) and superoxide anion radical (O2−). Benzene degradation products included hydroxylated derivatives of benzene (phenol, hydroquinone, benzoquinone, and catechol) and aliphatic acids (oxalic and fumaric acids). The proposed degradation pathways are consistent with radical formation and identified products. The investigation of selected matrix constituents showed that the Cl− and HCO3− had inhibitory effects on benzene degradation. Natural organic matter (NOM) had accelerating influence in degrading benzene. The developed system was tested with groundwater samples and it was found that the Fe(III)-activated SPC has a great potential in effective remediation of benzene-contaminated groundwater while more further studies should be done for its practical application in the future because of the complex subsurface environment