The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) i...The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH ) and Fe(Ⅳ) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(Ⅴ), in the solutions.展开更多
Microaerobic Fe(Ⅱ) oxidation process at neutral pH, driven by microbes can couple to carbon assimilation process in iron-rich freshwater and marine environments;however, few studies report such coupled processes in p...Microaerobic Fe(Ⅱ) oxidation process at neutral pH, driven by microbes can couple to carbon assimilation process in iron-rich freshwater and marine environments;however, few studies report such coupled processes in paddy soil of the critical zone in South China. In this study, rhizosphere soil from flooded paddy field was used as the inoculum to enrich the microaerophilic Fe(Ⅱ)-oxidizing bacteria(FeOB) in gradient tubes with different Fe(Ⅱ) substrates(FeS and FeCO_3) and ^(13)C-biocarbonate as inorganic carbon source to track the carbon assimilation. Kinetics of Fe(Ⅱ) oxidation and biomineralization were analyzed, and the composition and abundance of the microbial community were profiled using 16 S rRNA gene-based highthroughput sequencing. Results showed that microbial cell bands were formed 0.5–1.0 cm below the medium surface in the inoculated tubes with Fe(Ⅱ) substances, while no cell band was found in the non-inocula controls. The protein concentrations in the cell bands reached the highest values at 18.7–22.9 mg m^L(-1) on 6 d in the inocula tubes with Fe(Ⅱ) substrates. A plateau of the yields of ^(13)C-biocarbonate incorporation was observed during 6–15 d at 0.44–0.54% and 1.61–1.98% in the inocula tubes with FeS and FeCO_3, respectively. The inocula tube with FeS showed a higher Fe(Ⅱ) oxidation rate of 0.156 mmol L^(-1) d^(-1) than that with FeCO_3(0.106 mmol L^(-1) d^(-1)). Analyses of X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that amorphous iron oxide was formed on the surface of rod-shaped bacteria after Fe(Ⅱ) oxidation.Relative to the agar only control, the abundances of Clostridium and Pseudogulbenkiania increased in the inocula tube with FeS,while those of Vogesella, Magnetospirillum, Solitalea, and Oxalicibacterium increased in the inocula tube with FeCO_3, all of which might be the potential microaerophilic FeOB in paddy soil. The findings in this study suggest that microbes that couple microaerobic Fe(Ⅱ) oxidation to carbon assimilation existed in the paddy soil, which provides an insight into the iron-carbon coupling transformation under microaerobic conditions in the critical zone of the iron-rich red soil.展开更多
The Fe/N ratio is an important control on nitrate-reducing Fe(Ⅱ)oxidation processes that occur both in the aquatic environment and in wastewater treatment systems.The response of nitrate reduction,Fe oxidation,and mi...The Fe/N ratio is an important control on nitrate-reducing Fe(Ⅱ)oxidation processes that occur both in the aquatic environment and in wastewater treatment systems.The response of nitrate reduction,Fe oxidation,and mineral production to different initial Fe/N molar ratios in the presence of Paracoccus denitrificans was investigated in 132 h incubation experiments.A decrease in the nitrate reduction rate at 12 h occurred as the Fe/N ratio increased.Accumulated nitrite concentration at Fe/N ratios of 2–10 peaked at 12–84 h,and then decreased continuously to less than 0.1 mmol/L at the end of incubation.N_(2)O emission was promoted by high Fe/N ratios.Maximum production of N_(2) occurred at a Fe/N ratio of 6,in parallel with the highest mole proportion of N_(2) resulting from the reduction of nitrate(81.2%).XRD analysis and sequential extraction demonstrated that the main Fe minerals obtained from Fe(Ⅱ)oxidation were easily reducible oxides such as ferrihydrite(at Fe/N ratios of 1–2),and easily reducible oxides and reducible oxides(at Fe/N ratios of 3–10).The results suggest that Fe/N ratio potentially plays a critical role in regulating N_(2),N_(2)O emissions and Fe mineral formation in nitrate-reducing Fe(II)oxidation processes.展开更多
The membrane-associated c-type cytochromes(c-Cyts) have been well known as the key enzymes mediating extracellular electron transfer to terminal electron acceptors, resulting in biogeochemical elemental transformation...The membrane-associated c-type cytochromes(c-Cyts) have been well known as the key enzymes mediating extracellular electron transfer to terminal electron acceptors, resulting in biogeochemical elemental transformation, contaminant degradation, and nutrient cycling. Although c-Cyts-mediated metal reduction or oxidation have been mainly investigated with the purified proteins of metal reducing/oxidizing bacteria, the in vivo behavior of c-Cyts is still unclear, given the difficulty in measuring the proteins of intact cells. Fortunately, the in situ spectroscopy would be ideal for measuring the reaction kinetics of c-Cyts in intact cells under noninvasive physiological conditions. It can also help the establishment of kinetic/thermodynamic models of extracellular electron transfer processes, which are essential to understand the electron transfer mechanisms at the molecular scale. This review briefly summarizes the current advances in spectral methods for examining the c-Cyts in intact cells of dissimilatory metal reducing bacteria and Fe(Ⅱ)-oxidizing bacteria.展开更多
条带状铁建造(banded iron formations, BIFs)是早前寒武纪(3.8~1.8 Ga)缺氧古海洋中大规模Fe(Ⅱ)氧化形成的一类富铁沉积岩,具有典型的硅质层与铁质层互层的条带状或层状结构,形成的铁矿物主要以磁铁矿和赤铁矿为主。BIFs构成了全球规...条带状铁建造(banded iron formations, BIFs)是早前寒武纪(3.8~1.8 Ga)缺氧古海洋中大规模Fe(Ⅱ)氧化形成的一类富铁沉积岩,具有典型的硅质层与铁质层互层的条带状或层状结构,形成的铁矿物主要以磁铁矿和赤铁矿为主。BIFs构成了全球规模最大、储量最多的铁矿类型,具有重大的经济价值。BIFs也是地球环境与生命协同演化的产物,是研究早期地球许多重大演化事件(如大氧化事件)独特的载体。然而,由于早前寒武古海洋环境和沉积条件的独特性,尽管经过了近百年的研究,BIFs成因仍存在许多未解之谜。其中,最关键的科学问题莫过于溶解态Fe(Ⅱ)如何在缺氧古海洋中大量氧化形成特定的铁矿物组合。本文首先概述了BIFs类型、物质组成及来源,以及沉积条件等基本信息;然后从BIFs特殊的沉积环境入手,综述了前人提出的Fe(Ⅱ)氧化机理及存在的一些问题,讨论了微生物驱动下的氮元素生物地球化学循环对Fe(Ⅱ)氧化及BIFs形成的贡献及相关研究进展,最后对BIFs成因研究提出了展望。展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51574285)
文摘The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH ) and Fe(Ⅳ) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(Ⅴ), in the solutions.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41571130052, 41701295 & 41271263)the Guangdong Natural Science Funds for Distinguished Young Scholars (Grant No. 2017A030306010)
文摘Microaerobic Fe(Ⅱ) oxidation process at neutral pH, driven by microbes can couple to carbon assimilation process in iron-rich freshwater and marine environments;however, few studies report such coupled processes in paddy soil of the critical zone in South China. In this study, rhizosphere soil from flooded paddy field was used as the inoculum to enrich the microaerophilic Fe(Ⅱ)-oxidizing bacteria(FeOB) in gradient tubes with different Fe(Ⅱ) substrates(FeS and FeCO_3) and ^(13)C-biocarbonate as inorganic carbon source to track the carbon assimilation. Kinetics of Fe(Ⅱ) oxidation and biomineralization were analyzed, and the composition and abundance of the microbial community were profiled using 16 S rRNA gene-based highthroughput sequencing. Results showed that microbial cell bands were formed 0.5–1.0 cm below the medium surface in the inoculated tubes with Fe(Ⅱ) substances, while no cell band was found in the non-inocula controls. The protein concentrations in the cell bands reached the highest values at 18.7–22.9 mg m^L(-1) on 6 d in the inocula tubes with Fe(Ⅱ) substrates. A plateau of the yields of ^(13)C-biocarbonate incorporation was observed during 6–15 d at 0.44–0.54% and 1.61–1.98% in the inocula tubes with FeS and FeCO_3, respectively. The inocula tube with FeS showed a higher Fe(Ⅱ) oxidation rate of 0.156 mmol L^(-1) d^(-1) than that with FeCO_3(0.106 mmol L^(-1) d^(-1)). Analyses of X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy revealed that amorphous iron oxide was formed on the surface of rod-shaped bacteria after Fe(Ⅱ) oxidation.Relative to the agar only control, the abundances of Clostridium and Pseudogulbenkiania increased in the inocula tube with FeS,while those of Vogesella, Magnetospirillum, Solitalea, and Oxalicibacterium increased in the inocula tube with FeCO_3, all of which might be the potential microaerophilic FeOB in paddy soil. The findings in this study suggest that microbes that couple microaerobic Fe(Ⅱ) oxidation to carbon assimilation existed in the paddy soil, which provides an insight into the iron-carbon coupling transformation under microaerobic conditions in the critical zone of the iron-rich red soil.
基金This work was supported by the National Key R&D Program of China(No.2017YFC0505305)the Fundamental Research Funds for the Central Universities(No.2662018JC053).
文摘The Fe/N ratio is an important control on nitrate-reducing Fe(Ⅱ)oxidation processes that occur both in the aquatic environment and in wastewater treatment systems.The response of nitrate reduction,Fe oxidation,and mineral production to different initial Fe/N molar ratios in the presence of Paracoccus denitrificans was investigated in 132 h incubation experiments.A decrease in the nitrate reduction rate at 12 h occurred as the Fe/N ratio increased.Accumulated nitrite concentration at Fe/N ratios of 2–10 peaked at 12–84 h,and then decreased continuously to less than 0.1 mmol/L at the end of incubation.N_(2)O emission was promoted by high Fe/N ratios.Maximum production of N_(2) occurred at a Fe/N ratio of 6,in parallel with the highest mole proportion of N_(2) resulting from the reduction of nitrate(81.2%).XRD analysis and sequential extraction demonstrated that the main Fe minerals obtained from Fe(Ⅱ)oxidation were easily reducible oxides such as ferrihydrite(at Fe/N ratios of 1–2),and easily reducible oxides and reducible oxides(at Fe/N ratios of 3–10).The results suggest that Fe/N ratio potentially plays a critical role in regulating N_(2),N_(2)O emissions and Fe mineral formation in nitrate-reducing Fe(II)oxidation processes.
基金funded by the National Natural Science Foundations of China(41522105 and 41571130052)Guangdong Natural Science Funds for Distinguished Young Scholar(2014A030306041)Special Support Program(2016)
文摘The membrane-associated c-type cytochromes(c-Cyts) have been well known as the key enzymes mediating extracellular electron transfer to terminal electron acceptors, resulting in biogeochemical elemental transformation, contaminant degradation, and nutrient cycling. Although c-Cyts-mediated metal reduction or oxidation have been mainly investigated with the purified proteins of metal reducing/oxidizing bacteria, the in vivo behavior of c-Cyts is still unclear, given the difficulty in measuring the proteins of intact cells. Fortunately, the in situ spectroscopy would be ideal for measuring the reaction kinetics of c-Cyts in intact cells under noninvasive physiological conditions. It can also help the establishment of kinetic/thermodynamic models of extracellular electron transfer processes, which are essential to understand the electron transfer mechanisms at the molecular scale. This review briefly summarizes the current advances in spectral methods for examining the c-Cyts in intact cells of dissimilatory metal reducing bacteria and Fe(Ⅱ)-oxidizing bacteria.
文摘条带状铁建造(banded iron formations, BIFs)是早前寒武纪(3.8~1.8 Ga)缺氧古海洋中大规模Fe(Ⅱ)氧化形成的一类富铁沉积岩,具有典型的硅质层与铁质层互层的条带状或层状结构,形成的铁矿物主要以磁铁矿和赤铁矿为主。BIFs构成了全球规模最大、储量最多的铁矿类型,具有重大的经济价值。BIFs也是地球环境与生命协同演化的产物,是研究早期地球许多重大演化事件(如大氧化事件)独特的载体。然而,由于早前寒武古海洋环境和沉积条件的独特性,尽管经过了近百年的研究,BIFs成因仍存在许多未解之谜。其中,最关键的科学问题莫过于溶解态Fe(Ⅱ)如何在缺氧古海洋中大量氧化形成特定的铁矿物组合。本文首先概述了BIFs类型、物质组成及来源,以及沉积条件等基本信息;然后从BIFs特殊的沉积环境入手,综述了前人提出的Fe(Ⅱ)氧化机理及存在的一些问题,讨论了微生物驱动下的氮元素生物地球化学循环对Fe(Ⅱ)氧化及BIFs形成的贡献及相关研究进展,最后对BIFs成因研究提出了展望。
