Fe(III)的微生物异化还原

异化Fe(III)还原微生物是厌氧环境中广泛存在的一类主要微生物类群,它们的共同特征是可以利用Fe(III)作为末端电子受体而获能。异化Fe(III)还原微生物具有强大的代谢功能,可还原许多有毒重金属包括一些放射性核素,还可降解利用许多有机污染物,在污染环境的生物修复中具有重要的应用价值。本文对异化Fe(III)还原微生物的分布、分类,代谢功能多样性以及异化Fe(III)还原的意义做了评述,旨在加强相关领域的研究人员对此的了解和重视,通过学科的交叉和合作加快我国在这一领域的研究。     

微生物还原Cr(VI)的研究进展

随着现代工业的发展, 水环境中的重金属对人类健康和环境带来严重的危害, 其中的Cr(VI)具有强烈的毒性。微生物在代谢过程中可以将Cr(VI)还原为Cr(III), 有效降低Cr(VI)的毒性。本文从可还原Cr(VI)的微生物、微生物还原Cr(VI)的机理、还原过程中存在的问题及发展方向等方面进行了综述。     

异化铁还原细菌LQ25还原重金属Cr(Ⅵ)的特性研究

【背景】异化铁还原细菌能够在还原Fe(Ⅲ)的同时将毒性较大的Cr(Ⅵ)还原成毒性较小的Cr(Ⅲ),解决铬污染的问题。【目的】基于丁酸梭菌(Clostridiumbutyricum)LQ25异化铁还原过程制备生物磁铁矿,开展异化铁还原细菌还原Cr(Ⅵ)的特性研究。【方法】构建以氢氧化铁为电子受体和葡萄糖为电子供体的异化铁培养体系。菌株LQ25培养结束时制备生物磁铁矿。设置不同初始Cr(Ⅵ)浓度(5、10、15、25和30mg/L),分别测定菌株LQ25对Cr(Ⅵ)还原效率以及生物磁铁矿对Cr(Ⅵ)的还原效率。【结果】菌株LQ25在设置的Cr(Ⅵ)浓度范围内都能良好生长。当Cr(Ⅵ)浓度为15 mg/L时,在异化铁培养条件下,菌株LQ25对Cr(Ⅵ)的还原率为63.45%±5.13%,生物磁铁矿对Cr(Ⅵ)的还原率为87.73%±9.12%,相比菌株还原Cr(Ⅵ)的效率提高38%。pH变化能影响生物磁铁矿对Cr(Ⅵ)的还原率,当pH2.0时,生物磁铁矿对Cr(Ⅵ)的还原率最高,几乎达到100%。电子显微镜观察发现生物磁铁矿表面有许多孔隙,X-射线衍射图谱显示生物磁铁矿中Fe(II)的存在形式是Fe(OH)_2。【结论】基于异化铁还原细菌制备生物磁铁矿可用于还原Cr(Ⅵ),这是一种有效去除Cr(Ⅵ)的途径。     

细菌的Fe(Ⅲ)还原

细菌Fe(Ⅲ)还原是生物进化过程中最早出现的生物能量代谢途径,多种古细菌和真细菌具有Fe(Ⅲ)还原能力。在细菌Fe(Ⅲ)还原的过程中,需要多种膜蛋白的参与,且受到多途径的调控,特别是多血红素的细胞色素在电子传递过程中发挥重要作用。细菌Fe(Ⅲ)还原在生命的进化和整个生物地球化学循环中起到重要作用,具重要的环境学意义。     

Fe(Ⅲ)的微生物异化还原

异化Fe（Ⅲ）还原微生物是厌氧环境中广泛存在的一类主要微生物类群,它们的共同特征是可以利用Fe（Ⅲ）作为末端电子受体而获能。异化Fe（Ⅲ）还原微生物具有强大的代谢功能,可还原许多有毒重金属包括一些放射性核素,还可降解利用许多有机污染物,在污染环境的生物修复中具有重要的应用价值。本文对异化Fe（Ⅲ）还原微生物的分布、分类,代谢功能多样性以及异化Fe（Ⅲ）还原的意义做了评述,旨在加强相关领域的研究人员对此的了解和重视,通过学科的交叉和合作加快我国在这一领域的研究。     

异化铁还原细菌Clostridium sp.LQ25分离及其产氢与铁还原特性

[背景] 一些异化铁还原细菌兼具铁还原和发酵产氢能力,可作为发酵型异化铁还原细菌还原机制研究的对象。[目的] 筛选出一株发酵型异化铁还原细菌。在异化铁还原细菌培养体系中,设置不同电子供体并分析电子供体。[方法] 通过三层平板法从海洋沉积物中筛选纯菌株,基于16S rRNA基因序列进行菌株鉴定。通过测定细菌培养液Fe （II）浓度及发酵产氢量分析菌株异化铁还原和产氢性质。[结果] 菌株LQ25与Clostridium butyricum的16S rRNA基因序列相似性达到100%,结合电镜形态观察,菌株命名为Clostridium sp.LQ25。在氢氧化铁为电子受体培养条件下,菌株生长较对照组（未添加氢氧化铁）显著提高。菌株LQ25能够利用丙酮酸钠、葡萄糖和乳酸钠进行生长。丙酮酸钠为电子供体时,菌株LQ25细胞生长和异化铁还原效率最高,菌体蛋白质含量是（78.88±3.40） mg/L,累积产生Fe （II）浓度为（8.27±0.23） mg/L。以葡萄糖为电子供体时,菌株LQ25发酵产氢量最高,达（475.2±14.4） mL/L,相比对照组（未添加氢氧化铁）产氢量提高87.7%。[结论] 筛选到一株具有异化铁还原和发酵产氢能力的菌株Clostridium sp.LQ25,为探究发酵型异化铁还原细菌胞外电子传递机制提供了新的实验材料。     

海洋沉积物中铁还原细菌组成及异化铁还原与产氢性质分析

[背景]一些铁还原细菌具有异化铁还原与产氢的能力,该类细菌在环境污染修复的同时能够解决能源问题.[目的]从海洋沉积物中富集获得异化铁还原菌群,明确混合菌群组成、异化铁还原及产氢性质.获得海洋沉积物中异化铁还原混合菌群组成,分析菌群异化铁还原和产氢性质.[方法]利用高通量测序技术分析异化铁还原菌群的优势菌组成,在此基础上...     

Fe(III)的微生物异化还原*

异化Fe(III)还原微生物是厌氧环境中广泛存在的一类主要微生物类群,它们的共同特片是可以利用Fe(III)作为末端电子受体而获能。异化Fe(III)还原微生物具有强大的代谢功能;可还原许多有毒重金属包括一些放射性核素,还可降解利用许多有机污染物,在污酒女环境的生物修复中具有重要的应用价值。本文对异化Fe(III)还原微生物的分布、分类、代谢功能多样性以及异化Fe(III)还原的意义做了评述,旨在加强相关领域的研究人同对此的了解和重视,通过学科和交叉和合作加快我国在这一领域的研究。     

电子穿梭体对菌株Clostridium butyricum LQ25异化铁还原性质影响

【目的】在异化铁还原细菌培养体系中,通过外加电子穿梭体,分析电子穿梭体种类与浓度对细菌异化铁还原性质的影响。【方法】以一株发酵型异化铁还原细菌Clostridium butyricum LQ25为研究对象,设置水溶性介体蒽醌-2-磺酸钠和核黄素作为外加电子穿梭体。【结果】在氢氧化铁为电子受体、葡萄糖为电子供体培养条件下,不同浓度蒽醌-2-磺酸钠和核黄素对菌株LQ25异化铁还原效率影响具有显著性差异。外加蒽醌-2-磺酸钠浓度为0.5 mmol/L时,菌株累积产生Fe(Ⅱ)浓度最高,为12.95±0.08 mg/L,相比对照组提高88%。核黄素浓度为100mg/L时,菌株累积产生Fe(Ⅱ)浓度是11.06±0.04mg/L,相比对照组提高61%。外加电子穿梭体能够改变菌株LQ25发酵产物中丁酸和乙酸浓度,提高乙酸相对含量。【结论】蒽醌-2-磺酸钠和核黄素作为外加电子穿梭体能显著促进细菌异化铁还原效率,为揭示发酵型异化铁还原细菌胞外电子传递机制提供实验支持。     

一株李氏禾内生细菌去除Cr(VI)的特性

李氏禾(Leersia hexandra)是中国境内发现的第一种铬超积累植物,该文对李氏禾内生菌及其除铬性能进行了研究。采用添加Cr(VI)的牛肉膏蛋白胨固体平板培养方法,从李氏禾根部分离筛选获得一株具有较强Cr(VI)抗性的内生细菌G04,分子生物学鉴定结果表明该菌株属于阴沟肠杆菌(Enterobacter cloacae)。采用摇瓶培养方法,以Cr(VI)去除率、总Cr(铬)的去除率以及菌体生物量为指标,考察了pH、温度、底物浓度、装液量、接种量、摇床转速以及反应时间等因素对Cr(VI)去除率、总铬去除率和菌株生长的影响。结果表明:在牛肉膏蛋白胨液体培养基中,菌株E. cloacae G04去除Cr(VI)的较优反应条件为初始pH5. 0、温度37℃、Cr(VI)浓度为100 mg·L~(-1)、装液量80 mL(250 mL三角瓶)、接种量15%、摇床转速为120r·min~(-1)、反应时间48 h。在此条件下,菌株E. cloacae G04对Cr(VI)和总铬的去除率分别为84%和8%。根据Cr(VI)去除率和总铬去除率的结果推测该菌株去除Cr(VI)的机制可能是以还原为主、吸附为辅。这表明李氏禾内生细菌E. cloacae G04菌株具有较好的应用潜力,既有可能直接用于土壤、水环境铬污染的修复,也有可能作为促植物修复铬污染的后备菌株,另外可为深入研究李氏禾的铬积累作用机制提供参考。     

Modes of Biomineralization of Magnetite by Microbes

Biomineralization processes have traditionally been grouped into two distinct modes; biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). In BIM, microbes cause mineral formation by sorbing solutes onto their cell surfaces or extruded organic polymers and/or releasing reactive metabolites which alter the saturation state of the solution proximal to the cell or polymer surface. Such mineral products appear to have no specific recognized functions. On the other hand, in BCM microbes exert a great degree of chemical and genetic control over the nucleation and growth of mineral particles, presumably because the biominerals produced serve some physiological function. Interestingly, there are examples where the same biomineral is produced by both modes in the same sedimentary environment. For example, the magnetic mineral magnetite (Fe ₃ O ₄ ) is generated extracellularly in the bulk pore waters of sediments by various Fe(III)-reducing bacteria under anaerobic conditions, while some other anaerobic and microaerophilic bacteria and possibly protists form magnetite intracellularly within preformed vesicles. Differences in precipitation mechanisms might be caused by enzymatic activity at specific sites on the surface of the cell. Whereas one type of microbe might facilitate the transport of dissolved Fe(III) into the cell, another type will express its reductive enzymes and cause the reduction of Fe(III) external to the cell. Still other microbes might induce magnetite formation indirectly through the oxidation of Fe(II), followed by the reaction of dissolved Fe(II) with hydrolyzed Fe(III). The biomineralization of magnetite has significant effect on environmental iron cycling, the magnetization of sediments and thus the geologic record, and on the use of biomarkers as microbial fossils.     

Secondary Mineral Formation During Ferrihydrite Reduction by Shewanella oneidensis MR-1 Depends on Incubation Vessel Orientation and Resulting Gradients of Cells,Fe2+ and Fe Minerals

In previous studies on microbial ferric iron (Fe(III)) reduction varying results regarding reduction rates and secondary mineral formation have been reported for almost identical conditions regarding temperature, pH, medium composition, Fe(III) mineral identity and bulk iron concentration. Here we show that in addition to physico-chemical parameters also geometric aspects, i.e., incubation orientation and dimension of cultivation vessels, influence the reduction rates and mineralogy. We incubated the Fe(III)-reducer Shewanella oneidensis MR-1 in test tubes at ferrihydrite (FH) concentrations of 1.3–50 mM either in vertical or horizontal orientation. Cells and minerals formed a pellet at the bottom of the tubes with different thicknesses at the same initial FH concentration depending on the incubation orientation. In vertically incubated tubes thick FH pellets were present at the bottom of the tubes and magnetite was formed in all setups with ≥2.5 mM initial FH. In tubes that were incubated horizontally no magnetite was formed in presence of <5 mM initial FH. Spatially resolved analysis of the supernatant and mineral sediment including voltammetric microelectrodes, Xray diffraction and Mössbauer spectroscopy revealed strong gradients of Fe²⁺ in both the aqueous supernatant and mineral pellets, whereas a heterogeneous distribution of cells and minerals in the sediment pellet was detected. The highest cell density and, consequently, the initiation of FH reduction was found at the mineral-supernatant interface. This study demonstrates that small changes in incubation conditions can significantly influence and even change the experimental results of geomicrobiological experiments.     

Enumeration of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the root zone of wetland plants: Implications for a rhizosphere iron cycle

Iron plaque occurs on the roots of most wetland and submersed aquatic plant species and is a large pool of oxidized Fe(III) in some environments. Because plaque formation in wetlands with circumneutral pH has been largely assumed to be an abiotic process, no systematic effort has been made to describe plaque-associated microbial communities or their role in plaque deposition. We hypothesized that Fe(II)-oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB) are abundant in the rhizosphere of wetland plants across a wide range of biogeochemical environments. In a survey of 13 wetland and aquatic habitats in the Mid-Atlantic region, FeOB were present in the rhizosphere of 92% of the plant specimens collected (n = 37), representing 25 plant species. In a subsequent study at six of these sites, bacterial abundances were determined in the rhizosphere and bulk soil using the most probable number technique. The soil had significantly more total bacteria than the roots on a dry mass basis (1.4 × 10⁹ cells/g soil vs. 8.6 × 10⁷ cells/g root; p < 0.05). The absolute abundance of aerobic, lithotrophic FeOB was higher in the soil than in the rhizosphere (3.7 × 10⁶/g soil vs. 5.9 × 10⁵/g root; p < 0.05), but there was no statistical difference between these habitats in terms of relative abundance (1% of the total cell number). In the rhizosphere, FeRB accounted for an average of 12% of all bacterial cells while in the soil they accounted for < 1% of the total bacteria. We concluded that FeOB are ubiquitous and abundant in wetland ecosystems, and that FeRB are dominant members of the rhizosphere microbial community. These observations provide a strong rationale for quantifying the contribution of FeOB to rhizosphere Fe(II) oxidation rates, and investigating the combined role of FeOB and FeRB in a rhizosphere iron cycle.     

Chromium(VI)-reducing <Emphasis Type="Italic">Chlorella</Emphasis> spp. isolated from disposal sites of paper-pulp and electroplating industry

We isolated four cultures of chromate resistant, unicellular, non-motile green algae from disposal sites of the paper-pulp and electroplating industries. These algae were maintained in Tris-acetate-glycerophosphate medium containing 30 μM K₂Cr₂O₇. The morphological features as well as analysis of the 500-bp fragment of 18S rDNA (NS 12 region) showed that these isolates belong to Chlorella spp. These isolates showed EC₅₀ values for chromate ranging from 60 to 125 μM. Uptake studies with radioactive ⁵¹Cr(VI) showed that 10–19% of total radioactivity was intracellular, and 1–2% was bound to the cell wall. The rest of the activity remained in the medium, suggesting that resistance was not related to accumulation of Cr(VI) in the cells. Interestingly, when these isolates were grown in the presence of 30 μM of K₂Cr₂O₇, a decrease in the Cr(VI) concentration in the medium was observed. Only live cells could deplete Cr(VI) from the supernatant, suggesting the presence of chromium reduction activity in these Chlorella isolates. Cr(VI) reduction activity of the cells of Chlorella was stimulated by light as well as by acetate and glycerophosphate. Treatment of Chlorella cells with 3-(3,4 dichlorophenyl),1,1dimethyl urea (DCMU) did not affect the Cr(VI) reduction. However, if the cells were treated with sodium azide, Cr(VI) reduction was severely affected. Though chromate resistance has been well documented in algae, the information on chromate reduction by algae is scant. This paper discusses the Cr(VI) reduction by Cr(VI) resistant Chlorella, which may find a use in the effective bioremediation of Cr(VI).     

Bacterial Cr(VI) Reduction Concurrently Improves Sunflower (<Emphasis Type="Italic">Helianthus Annuus</Emphasis> L.) Growth

Four Cr(VI)-reducing bacterial strains (Ochrobactrum intermedium, CrT-2, CrT-3 and CrT-4) previously isolated from chromium-contaminated sites were inoculated on to seeds of sunflower (Helianthus annuus var SF-187), which were germinated and grown along with non-inoculated controls with chromate salts (300 μg CrCl₃ or K₂CrO₄ ml⁻¹). Severe reduction (20%) in seed germination was observed in Cr(VI) stress. Plant height decreased (36%) with Cr(VI) when compared with chromium-free control, while O. intermedium inoculation resulted a 20% increment in this parameter as compared to non-inoculated chromium-free control. CrT-3 inoculation resulted a 69% increment in auxin content as compared to non-inoculated control. O. intermedium caused 30% decrease in chromium uptake in sunflower plant roots under Cr(VI) stress as compared to chromium-free control plants.     

The influence of chelating agents upon the dissimilatory reduction of Fe(III) byShewanella putrefaciens. Part 2. Oxo-and hydroxo-bridged polynuclear Fe(III) complexes

The susceptibility to dissimilatory reduction of polynuclear oxo- and hydroxo-bridged Fe(III) complexes byShewanella putrefaciens intact cells and membranes has been investigated. These complexes were ligated by the potential tetradentates heidi (H₃heidi =N-(2-hydroxyethyl)iminodiacetic acid) or nta (H₃nta = nitrilotriacetic acid), or the potential tridentate ida (H₂ida = iminodiacetic acid). A number of defined small complexes with varied nuclearity and solubility properties were employed, as well as undefined species prepared by mixing different molar ratios of ida or heidi:Fe(III) in solution. The rates of Fe(III) reduction determined by an assay for Fe(II) formation with ferrozine were validated by monitoringc-type cytochrome oxidation and re-reduction associated with electron transport. For the undefined Fe(III) polymeric species, reduction rates in whole cells and membranes were considerably faster in the presence of heidi compared to ida. This is believed to result from generally smaller and more reactive clusters forming with heidi as a consequence of the alkoxo function of this ligand being able to bridge between Fe(III) nuclei, with access to an Fe(III) reductase located at the cytoplasmic membrane being of some importance. The increases in reduction rates of the undefined ida species with Fe(III) using membranes relative to whole cells reinforce such a view. Using soluble synthetic Fe(III) clusters, slow reduction was noted for an oxo-bridged dimer coordinatively saturated with ida and featuring unligated carboxylates. This suggests that sterically hindering the cation can influence enzyme action. A heidi dimer and a heidi multimer (17 or 19 Fe(III) nuclei), which are both of poor solubility, were found to be reduced by whole cells, but dissimilation rates increased markedly using membranes. These data suggest that Fe(III) reductase activity may be located at both the outer membrane and the cytoplasmic membrane ofS. putrefaciens. Slower reduction of the heidi multimer relative to the heidi dimer reflects the presence of a central hydroxo(oxo)-bridged core containing nine Fe(III) nuclei within the former cluster. This unit is a poor substrate for dissimilation, owing to the fact that the Fe(III) is not ligated by aminocarboxylate. The faster reduction noted for the heidi dimer in membranes than for a soluble ida monomer suggests that the presence of ligating water molecules may relieve steric hindrance to enzyme attack. Furthermore, reduction of an insoluble oxo-bridged nta dimer featuring ligating water molecules in intact cells was faster than that of a soluble monomer coordinatively saturated by nta and possessing an unligated carboxylate. This suggests that steric factors may override solubility considerations with respect to the susceptibility to reduction of certain Fe(III) complexes by the bacterium.Previous paper in this series: Dobbin PS, Powell AK, McEwan AG, Richardson DJ. 1995 The influence of chelating agents upon the dissimilatory reduction of Fe(III) byShewanella putefraciens.BioMetals 8, 163–173.     

Reduction of diverse electron acceptors by Aeromonas hydrophila

Aeromonas hydrophila ATCC 7966 grew anaerobically on glycerol with nitrate, fumarate, Fe(III), Co(III), or Se(VI) as the sole terminal electron acceptor, but did not ferment glycerol. Final cell yields were directly proportional to the amount of terminal electron acceptor provided. Twenty-four estuarine mesophilic aeromonads were isolated; all reduced nitrate, Fe(III), or Co(III), and five strains reduced Se(VI). Dissimilatory Fe(III) reduction by A. hydrophila may involve cytochromes. Difference spectra obtained with whole cells showed absorption maxima at wavelengths characteristic of c-type cytochromes (419, 522, and 553 nm). Hydrogen-reduced cytochromes within intact cells were oxidized by the addition of Fe(III) or nitrate. Studies with respiratory inhibitors yielded results consistent with a respiratory chain involving succinate (flavin-containing) dehydrogenase, quinones and cytochromes, and a single Fe(III) reductase. Neither anaerobic respiration nor dissimilatory metal reduction by members of the genus Aeromonas have been reported previously. Received: 24 June 1997 / Accepted: 20 October 1997