微氧生物亚铁氧化及其重金属固定效应研究进展

铁的生物地球化学循环对于多种环境过程至关重要,如碳封存、温室气体排放以及营养元素和有毒金属的迁移和转化。近年来,随着分离培养方式及分子生物学方法的发展,作为铁循环的重要组成部分的微氧生物铁氧化的研究取得了显著的进展。微氧型亚铁氧化菌广泛分布于近中性环境中,其分离栖息地从地下水、湿地、溪流延展至深海环境。微氧生物亚铁氧化成矿过程主要发生在细胞表面,生成比表面积较大的无定型铁氧化物。大部分微氧型亚铁氧化菌通过形成鞘状或螺旋柄状结构的胞外多聚物吸附生成的铁氧化物,防止自身被铁氧化物包埋,导致无法正常代谢而死亡。亚铁氧化成矿过程可吸附和共沉淀重金属元素,降低重金属的移动性和生物可利用性,从而缓解重金属的污染,为治理环境污染提供新的思路。文章主要总结了近年来国内外对嗜中性微氧型亚铁氧化菌的研究进展,包括其代谢特征、种类及分布、以及亚铁氧化菌的成矿机制和成矿过程对重金属迁移转化的影响。最后对如何快速有效地分离微氧型亚铁氧化菌、明确成矿过程中的特殊结构的形成机制等问题进行了讨论和展望。     

水稻土中铁的厌氧生物氧化还原循环对砷的影响（The Effect of Anaerobic Redox Cycling of Iron on Arsenic Mobility in Paddy）

应用砷污染水稻土的厌氧富集培养,探讨水稻土中潜在存在铁厌氧生物循环及其对氮和砷的耦合作用.富集培养直接证明了水稻土中铁的厌氧生物循环:三价铁(人工合成针铁矿)在厌氧条件下被逐渐还原成二价铁;铁还原过程结束并外源添加硝酸根时,培养基中新生的二价铁在依赖于硝酸根的铁氧化菌的作用下被氧化;当提供新的电子供体乙酸时,生物合成的铁矿重新被还原.在铁氧化还原循环过程中,随着铁的还原,培养基中砷的浓度不断增加,反之,当铁逐渐氧化的同时不断地吸附固定培养基中的砷.在铁的厌氧氧化阶段,铁氧化的同时硝酸根被还原,培养基中积累了NH4+和NO2-.因此,厌氧水稻土中可以进行完整的铁氧化还原循环,同时这个循环过程耦合了氮和砷的迁移转化.     

硫酸盐还原菌介导针铁矿表面硫的转化及镉固定脱毒效应

土壤重金属镉(Cd)污染问题日益严重,已对农产品及人类健康造成严重威胁,研究Cd污染土壤修复技术具有重要环境意义。微生物修复技术,如硫酸盐还原菌(sulfate reducing bacteria,SRB)介导下重金属的固定技术,是土壤Cd污染控制修复的主要途径。而土壤中硫和铁均具有较高的地球化学活性,与重金属的脱毒转化密切相关。然而,目前关于铁物种、铁氧化物和SRB共存的情况下,重金属还原固定行为还缺乏深入的研究。文章通过构建"SRB-针铁矿-重金属"的交互反应体系,研究体系中硫的转化、铁还原、重金属镉的环境行为以及矿物物相变化,并对其作用机制进行初步探讨。结果表明,纯化学(针铁矿+FeCl_2+CdCl_2)培养条件下,体系并未发生明显的铁还原和硫酸盐还原过程,90%以上的重金属Cd以游离态形式存在;在SRB作用下(针铁矿+SRB),体系中硫酸盐和针铁矿均被迅速还原,在反应30 d时,66.34%硫酸盐被还原,同时生成2.17 mmol·L~(-1) Fe(Ⅱ);添加Cd Cl_2(针铁矿+CdCl_2+SRB),抑制了硫酸盐还原和铁还原过程,反应30 d后,体系中62.21%硫酸盐被还原,约50.65%的游离态的Cd(Ⅱ)可被吸附固定到矿物中。然而,外加FeCl_2可加速SRB对硫酸盐和针铁矿的还原,同时也可进一步促进游离态的Cd(Ⅱ)固定脱毒,其去除率可达66.89%(针铁矿+FeCl_2+CdCl_2+SRB)。矿物形貌和结构的表征显示,在SRB介导硫酸盐还原过程中,矿物的物相仍以针铁矿为主,另有Cd S固体生成。以上研究结果可为深入理解土壤中重金属的环境行为,研发高效的重金属脱毒技术提供科学依据。     

微生物介导的硝酸盐还原耦合亚铁氧化成矿研究进展

铁氧化微生物驱动的亚铁氧化过程是铁循环的重要组成部分。在中性厌氧环境中,硝酸盐还原亚铁氧化微生物可通过还原硝酸盐耦合氧化亚铁的过程影响污染物的降解及重金属的迁移转化等,对环境保护具有重要意义。文章主要综述了近年来有关硝酸盐还原亚铁氧化微生物驱动的不同形态亚铁氧化的成矿过程,成矿机制及其对微生物和环境的影响等。在亚铁氧化成矿的过程中,有机配体态和固态亚铁的氧化成矿主要发生在细胞表面,而小分子的无机溶解态亚铁还可继续进入细胞周质甚至细胞内膜氧化成矿。不同的培养条件(如缓冲液)和微生物种类也会影响成矿过程的反应速率从而影响矿物的结晶度。根据成矿的氧化剂不同,将成矿机制分为硝酸盐还原产物亚硝酸盐与亚铁反应的化学成矿机制与微生物利用铁氧化酶直接氧化亚铁的生物成矿机制。此外,硝酸盐还原耦合亚铁氧化成矿过程中所产生的细胞表面结壳现象,影响了不同微生物的新陈代谢过程,甚至会导致细胞死亡。而对于环境中的污染物,成矿过程可吸附和共沉淀多种重金属,从而降低重金属的污染,为治理环境污染提供了新思路。文章还分别对如何进行成矿过程的微观机制及其贡献的评估研究,以及如何更有效地利用成矿过程于环境污染治理中等问题进行了讨论和展望。     

微生物砷代谢机制的研究进展（Progress in Study of Mechanisms of Microbial Arsenic Transformation in Environment）

环境砷污染是一个全球性问题.研究砷的生物地球化学循环可以明确环境中砷的来源及其转化特征,为探索砷污染治理的方法提供参考.越来越多的研究表明,自然界中的微生物在砷的迁移转化过程中发挥了重要作用.根据微生物对砷的代谢机制不同将其分为:砷氧化微生物、砷还原微生物和砷甲基化微生物.砷氧化微生物可以将环境中的As(Ⅲ)氧化为毒性较弱并且容易被铁铝矿物吸附固定的As(Ⅴ),因此对降低环境中的砷毒性具有重要作用;微生物对砷的甲基化作用的产物通常为毒性较低的有机砷,因此也被认为是理想的修复环境砷污染的生物手段之一;然而在还原环境中,砷还原微生物却可以将游离态和结合态的As(Ⅴ)还原为毒性更强的As(Ⅲ),从而加重环境中的砷污染状况.由此可见,明确微生物的砷代谢机制及其对砷污染环境中砷迁移转化的影响,是实现生物修复砷污染环境的必要前提.论文总结了近年来国内外微生物砷代谢机制的研究进展,以期为深入研究微生物代谢砷的机理及其在砷污染治理中的应用提供参考.     

铁基生物炭钝化Cd大田试验研究

近年来,稻田Cd污染引起的环境及健康问题日益突出。应用钝化技术对土壤中有效性Cd进行钝化对稻田生态系统中Cd的生物地球化学循环具有重要的理论和实际意义。在广东省韶关市仁化县董塘镇红星村一受Cd污染的稻田上,设置大田试验,研究铁基生物炭对Cd在大田土壤-水稻系统迁移的影响以及对作物产量的影响。试验共设6个处理:(1)空白对照;(2)每一季水稻插秧前,一次性施加1500 kg·hm^-2的普通生物炭;(3)每一季水稻插秧前,一次性施加75 kg·hm^-2的零价铁(Fe0);(4)每一季水稻插秧前,一次性施加1500 kg·hm^-2、ω(Fe)=1%的铁基生物炭(ω(Fe)=1%in Fe-Biochar);(5)每一季水稻插秧前,一次性施加1500 kg·hm^-2、ω(Fe)=3%的铁基生物炭(ω(Fe)=3%in Fe-Biochar);(6)每一季水稻插秧前,一次性施加1500 kg·hm^-2、ω(Fe)=5%的铁基生物炭(ω(Fe)=5%in Fe-Biochar)。结果表明:(1)施用生物炭、铁粉和铁基生物炭土壤钝化调理剂可以增加水稻产量,显著降低籽粒重金属Cd含量;(2)施用铁基生物炭可以显著增加水稻根表铁膜Fe含量,同时显著增加水稻根表铁膜固定的Cd量,抑制重金属Cd向籽粒的运输累积。综合考虑施用成本和钝化效果,对于Cd污染稻田,建议施用1500 kg·hm^-2、ω(Fe)=3%的铁基生物炭材料。     

铁氨氧化研究进展及在污水脱氮中的应用探索

近几年来，铁氨氧化(Feammox)反应在不同的环境体系中相继被发现. Feammox反应是在厌氧环境中以及微生物的驱使作用下，NH₄⁺和Fe(Ⅲ)分别作为电子供体和电子受体，Fe(Ⅲ)被还原生成为Fe(Ⅱ)，而NH₄⁺则转化生成为亚硝酸盐(NO₂^-)、硝酸盐(NO₃^-)和氮气(N₂)几种不同形态的氮素.Feammox的发现进一步揭示了氮素在自然界循环中的新的转化途径，这种新的氮素转换途径给污水领域中的脱氮技术方法带来了全新视角.另外，Feammox能够和厌氧氨氧化(Anammox)和铁型反硝化(NDFO)耦合或者通过实现Fe(Ⅲ)和Fe(Ⅱ)之间的循环转化进行脱氮，使得Feammox成为了一种潜在的新型脱氮技术.通过综述Feammox的发展历程、反应机制、以及对自然界生态系统所产生的的影响和其所受影响的物理性因素，最后，进一步探讨Feammox在污水脱氮中的应用，并对其未来发展进行总结和展...     

电子穿梭体及其介导的环境与地球化学过程研究进展

电子穿梭体是一类可通过自身氧化还原介导电子转移的化学物质的统称。在地球表层系统中,电子穿梭体可加速微生物向细胞外部进行的电子传递,参与矿物的微生物还原,驱动碳、氮、硫元素循环,并偶联有机污染物降解和重金属迁移转化。电子穿梭在自然界中存在广泛,对于元素循环、污染物环境行为以及微生物的生存行为影响深远,具有重要的环境地球化学意义。因此,该文以自然界存在的典型电子穿梭体为阐述对象,综述了以腐殖质、硫单质和生物炭为代表的三类典型穿梭体的反应特性。其中,腐殖质是土壤中天然存在的分布最广的穿梭体,硫单质是碱性环境下最典型的穿梭体,而生物炭则是稻田系统中人为输入的穿梭体。以上述三类穿梭体为核心,该文系统阐述了穿梭过程与碳氮循环、铁循环和污染物迁移转化的相互关系、以及穿梭体对微生物菌群变化产生的影响。在碳氮循环过程中,穿梭体主要参与有机碳的厌氧消耗、二氧化碳向甲烷的转化、氨氧化以及氧化亚氮向氮气的转化过程;在铁循环过程中,穿梭体主要影响氧化铁的还原溶解、含铁矿物的晶型转变以及氧化铁还原耦合的砷、铬污染物转化过程;而穿梭体作为电子受体,还可改变微生物的生长与竞争关系,调控微生物菌群。文章深入分析了穿梭过程在地球表层系统中产生的环境效应与生态效应,并提出了本领域今后需关注的重点,可为穿梭行为的进一步研究提供思考依据。     

基于铁还原菌的微生物燃料电池研究进展

微生物燃料电池(Microbial fuel cell, MFC)是未来理想的发电装置,而铁还原菌是目前MFC研究中重要的产电微生物.自然界中并无微生物产电的直接进化压力,而MFC电极与自然界中Fe(III)氧化物同为难溶性胞外电子受体,研究表明,铁还原菌对二者的还原有相似机制.基于铁还原菌的MFC具有无需外加介体,可利用多种有机电子供体作为燃料,能量转化率高等优点.本文分析了铁还原菌还原电极和还原Fe(III)氧化物机制的相似性,对近年来基于各种铁还原菌的MFC研究进展进行分述和总结,提出了铁还原菌MFC的发展趋势和研究方向.     

黑锰矿催化氧化Fe(Ⅱ)生成铁氧化物过程及影响因素

自然界中的锰氧化物常与铁氧化物交结伴生，其形成和转化过程相互影响. Mn(Ⅳ)氧化物与Fe(Ⅱ)反应过程已有较多研究，然而有氧环境中低价锰氧化物氧化Fe(Ⅱ)生成铁氧化物的过程尚缺乏系统研究.本工作以黑锰矿为例，研究了开放体系中Fe(Ⅱ)在低价氧化锰矿物表面的氧化行为，分析了Fe(Ⅱ)浓度、溶解氧以及pH对Fe(Ⅲ)氧化物形成的影响.结果表明，黑锰矿在氧化Fe(Ⅱ)形成针铁矿和纤铁矿的同时，自身被部分还原释放Mn(Ⅱ).当反应体系pH值为3.0时，溶解氧氧化Fe(Ⅱ)作用弱，主要为黑锰矿氧化Fe(Ⅱ)并在其表面生成针铁矿.当反应体系pH值升高至5.0，黑锰矿催化加速了溶解氧对低浓度(<5.0 mmol·L^-1)Fe(Ⅱ)的氧化并生成水铁矿，随后转化成纤铁矿和针铁矿；Fe(Ⅱ)浓度升高(>5.0 mmol·L^-1)，反应初期Fe(Ⅱ)直接被黑锰矿氧化，形成了以针铁矿和少量纤铁矿组成的包覆层，并导致氧化速率减弱，而溶解氧在Fe(Ⅱ)后期氧化过程中发挥了主导作用.这些结果丰富了表生环境铁锰氧化物的形成与共生机理，为土壤矿物形成演化提供了...     

Comparison of different valent iron on anaerobic sludge digestion: Focusing on oxidation reduction potential,dissolved organic nitrogen and microbial community

• ORP value from −278.71 to −379.80 mV showed indiscernible effects on methane yield. • Fe(II) and Fe(III) promoted more degradation of proteins and amino acids than Fe⁰. • The highest enrichment of Geobacter was noted in samples added with Fe⁰. • Cysteine was accumulated during iron enhanced anaerobic sludge digestion. • Both iron content and valence were important for methane production. This study compared effects of three different valent iron (Fe⁰, Fe(II) and Fe(III)) on enhanced anaerobic sludge digestion, focusing on the changes of oxidation reduction potential (ORP), dissolved organic nitrogen (DON), and microbial community. Under the same iron dose in range of 0−160 mg/L after an incubation period of 30 days (d), the maximum methane production rate of sludge samples dosed with respective Fe⁰, Fe(II) and Fe(III) at the same concentration showed indiscernible differences at each iron dose, regardless of the different iron valence. Moreover, their behavior in changes of ORP, DON and microbial community was different: (1) the addition of Fe⁰ made the ORP of sludge more negative, and the addition of Fe(II) and Fe(III) made the ORP of sludge less negative. However, whether being more or less negative, the changes of ORP may show unobservable effects on methane yield when it ranged from −278.71 to −379.80 mV; (2) the degradation of dissolved organic nitrogen, particularly proteins, was less efficient in sludge samples dosed with Fe⁰ compared with those dosed with Fe(II) and Fe(III) after an incubation period of 30 d. At the same dose of 160 mg/L iron, more cysteine was noted in sludge samples dosed with Fe(II) (30.74 mg/L) and Fe(III) (27.92 mg/L) compared with that dosed with Fe⁰ (21.75 mg/L); (3) Fe⁰ particularly promoted the enrichment of Geobacter, and it was 6 times higher than those in sludge samples dosed with Fe(II) and Fe(III) at the same dose of 160 mg/L iron.     

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time (EBCT), and initial Cr(VI) concentration on Cr(VI) reduction were studied. The results showed that the pH, EBCT, and initial Cr(VI) concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57 mg Cr(VI)·g^-1 Fe⁰ at pH 3, 5, and 7 (initial Cr(VI) concentration 4 mg·L^-1, EBCT 2 min, and temperature 25°C), 0.51, 1.51, and 2.85 mg Cr(VI)·g^-1 Fe⁰ at EBCTs of 0.5, 2.0, and 6.0 min (initial Cr(VI) concentration 4 mg·L^-1, pH 5, and temperature 25°C), and 2.99, 1.51, and 1.01 mg Cr(VI)·g^-1 Fe⁰ at influent concentrations of 1, 4, and 8 mg·L^-1 (EBCT 2 min, pH 5, and temperature 25°C), respectively. Fe(total) concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr(VI) ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr⁶⁺·g^-1 Fe. Scanning electron microscope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.     

渭河流域关中段地表水重金属的污染特征与健康风险评价

由于重金属的毒理性及其对水生生态系统的重要影响,水生环境的重金属污染已成为全世界关注的问题.渭河是黄河的第一大支流,近年来随着沿岸社会经济的发展,渭河的水质受到严重的威胁,但是对渭河流域地表水重金属的污染状况缺乏全面评估.以渭河流域关中段为研究区域,采集了该流域35个地表水样品,检测了12种重金属元素(Cr、Mn、Fe...     

Heavy metals availability (Fe, Mn, Zn, Cu and Cr) in Aden Gulf sediments under aerobic and anaerobic conditions

The present study aims to analyse the chemical speciation of heavy metals in relation to aerobic and anaerobic conditions. Two sediment samples (from the Gulf of Aden, Yemen) were incubated under flooded conditions. In particular, the chemical forms of Fe, Mn, Zn, Cu and Cr under the experimental conditions were studied using a sequential chemical extraction method. The pH and Eh of the suspension were measured as critical parameters controlling the fate of the metals in the environment. The results showed that the metals concentration in the different forms varied with time incubation and affected by the variation of redox potential and pH value. Also, the changes in both redox potential (Eh) and pH values had evident effects on heavy metals transformation. It is obvious that the highest redox potential affected the amount of iron and manganese in the oxides form. When the redox potential decreased to-133 and-170 mV, it caused a significant transformation of the Fe-Mn oxide form to the water-soluble and exchangeable fractions. Under anaerobic conditions, the relative percentage of all five metals including the summation of four fractions (the water-soluble and exchangeable, carbonate, oxides and organic fractions) constituted 45-60% of the total amount of iron, 33-50% for manganese, 33-63% for Zn, 63-74% for Cu and 19-43% for Cr. Both zinc and copper among water-soluble and exchangeable fraction were high at the end of incubation period, this accompanied by a significant decrease in the content of the organically bound fraction. In general, the reducing conditions were more favorable for metal bound to water soluble and exchangeable fraction.     

Sulfur mediated heavy metal biogeochemical cycles in coastal wetlands: From sediments,rhizosphere to vegetation

• In sediments, the transformation of sulfides may lead to the release of heavy metals. • In the rhizosphere, sulfur regulates the uptake of heavy metals by plants. • In plants, sulfur mediates a series of heavy metal tolerance mechanisms. • Explore interactions between sulfur and heavy metals on different scales is needed. The interactions and mechanisms between sulfur and heavy metals are a growing focus of biogeochemical studies in coastal wetlands. These issues underline the fate of heavy metals bound in sediments or released into the system through sediments. Despite the fact that numerous published studies have suggested sulfur has a significant impact on the bioavailability of heavy metals accumulated in coastal wetlands, to date, no review article has systematically summarized those studies, particularly from the perspective of the three major components of wetland ecosystems (sediments, rhizosphere, and vegetation). The present review summarizes the studies published in the past four decades and highlights the major achievements in this field. Research and studies available thus far indicate that under anaerobic conditions, most of the potentially bioavailable heavy metals in coastal wetland sediments are fixed as precipitates, such as metal sulfides. However, fluctuations in physicochemical conditions may affect sulfur cycling, and hence, directly or indirectly lead to the conversion and migration of heavy metals. In the rhizosphere, root activities and microbes together affect the speciation and transformation of sulfur which in turn mediate the migration of heavy metals. As for plant tissues, tolerance to heavy metals is enhanced by sulfur-containing compounds via promoting a series of chelation and detoxification processes. Finally, to further understand the interactions between sulfur and heavy metals in coastal wetlands, some major future research directions are proposed.     

红壤胶体铁氧化物界面有机氯的非生物转化研究进展

综述了红壤胶体铁氧化物的结构、形态及其转化;铁氧化物界面有机氯的非生物转化过程及其影响因素;异化铁还原作用下的有机氯转化过程。有机氯的非生物转化主要包括氧化转化与脱氯转化过程。氧化转化包括暗态下的化学氧化与光化学氧化过程;脱氯转化包括脱氢卤化、加氢脱氯、脱双卤、二聚脱氯与亲核置换脱氯等反应过程。有机氯的非生物转化主要受胶体界面pH、Eh、水溶性有机物、金属离子、铁氧化物形态与铁还原细菌等的显著影响。有机氯非生物转化的化学-微生物耦合机制、复合污染条件下重金属对界面有机氯非生物转化过程的影响机制、红壤胶体界面有机氯污染的综合调控技术方法等三个方面值得关注,有助于推动土壤胶体界面环境化学的发展。     

Visible light induces bacteria to produce superoxide for manganese oxidation

● Term of manganese-oxidizing microorganisms should be reconsidered. ● Visible light induces heterotrophic bacteria to produce superoxide. ● Heterotrophic bacteria oxidize Mn(II) ions with a fast oxidation rate. ● Superoxide oxidizing Mn(II) ions is an unintended side reaction of bacteria. ● Superoxide is an important oxidation force of Mn(II) in the environment. Manganese oxides are widely distributed in soils and sediments, affecting the migration and transformation of heavy metals and organic pollutants. The microbial conversion of soluble Mn(II) into insoluble Mn(III/IV) oxides is considered to be the initial source of manganese oxides in the environment; however, whether this process is related to a physiological role remains unclear. Here, we explored the microbial manganese oxidation process under visible light by using coastal surface seawater microorganisms. Visible light greatly promotes the oxidation rate of Mn(II), and the average rate reaches 64 μmol/(L·d). The generated manganese oxides were then conducive to Mn(II) oxidation, thus the rapid manganese oxidation was the result of the combined action of biotic and abiotic, and biological function accounts for 88 % ± 4 %. Extracellular superoxide produced by microorganisms induced by visible light is the decisive factor for the rapid manganese oxidation in our study. But the production of these superoxides does not require the presence of Mn(II) ions, the Mn(II) oxidation process was more like an unintentional side reaction, which did not affect the growth of microorganisms. More than 70 % of heterotrophic microorganisms in nature are capable of producing superoxide, based on the oxidizing properties of free radicals, all these bacteria can participate in the geochemical cycle of manganese. What’s more, the superoxide oxidation pathway might be a significant natural source of manganese oxide.     

Redox reactions of iron and manganese oxides in complex systems

• Mechanisms of redox reactions of Fe- and Mn-oxides were discussed. • Oxidative reactions of Mn- and Fe-oxides in complex systems were reviewed. • Reductive reaction of Fe(II)/iron oxides in complex systems was examined. • Future research on examining the redox reactivity in complex systems was suggested. Conspectus Redox reactions of Fe- and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments. Due to experimental and analytical challenges associated with complex environments, there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems, and most of the studies so far have only focused on simple model systems. To bridge the gap between simple model systems and complex environmental systems, it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation. In this Account, we primarily focused on (1) the oxidative reactivity of Mn- and Fe-oxides and (2) the reductive reactivity of Fe(II)/iron oxides in complex model systems toward contaminant degradation. The effects of common metal ions such as Mn²⁺ , Ca²⁺, Ni²⁺, Cr³⁺ and Cu²⁺, ligands such as small anionic ligands and natural organic matter (NOM), and second metal oxides such as Al, Si and Ti oxides on the redox reactivity of the systems are briefly summarized.     

Magnetotactic bacteria: Characteristics and environmental applications

• Magnetotactic bacteria (MTB) synthesize magnetic nanoparticle within magnetosomes. • The morphologic and phylogenetic diversity of MTB were summarized. • Isolation and mass cultivation of MTB deserve extensive research for applications. • MTB can remove heavy metals, radionuclides, and organic pollutants from wastewater. Magnetotactic bacteria (MTB) are a group of Gram-negative prokaryotes that respond to the geomagnetic field. This unique property is attributed to the intracellular magnetosomes, which contains membrane-bound nanocrystals of magnetic iron minerals. This review summarizes the most recent advances in MTB, magnetosomes, and their potential applications especially the environmental pollutant control or remediation. The morphologic and phylogenetic diversity of MTB were first introduced, followed by a critical review of isolation and cultivation methods. Past research has devoted to optimize the factors, such as oxygen, carbon source, nitrogen source, nutrient broth, iron source, and mineral elements for the growth of MTB. Besides the applications of MTB in modern biological and medical fields, little attention was made on the environmental applications of MTB for wastewater treatment, which has been summarized in this review. For example, applications of MTB as adsorbents have resulted in a novel magnetic separation technology for removal of heavy metals or organic pollutants in wastewater. In addition, we summarized the current advance on pathogen removal and detection of endocrine disruptor which can inspire new insights toward sustainable engineering and practices. Finally, the new perspectives and possible directions for future studies are recommended, such as isolation of MTB, genetic modification of MTB for mass production and new environmental applications. The ultimate objective of this review is to promote the applications of MTB and magnetosomes in the environmental fields.