2022, Vol. 62
表1(Table 1)
细菌六价铬还原及吸附机制研究进展
http://dx.doi.org/10.13343/j.cnki.wsxb.20220144
中国科学院微生物研究所，中国微生物学会
中国科学院微生物研究所，中国微生物学会
文章信息
- 施国静, 吴效俭, 王莹莹. 2022
- SHI Guojing, WU Xiaojian, WANG Yingying.
- 细菌六价铬还原及吸附机制研究进展
- Mechanism of bacterial reduction and biosorption of hexavalent chromium
- 微生物学报, 62(11): 4287-4304
- Acta Microbiologica Sinica, 62(11): 4287-4304
-
文章历史
- 收稿日期：2022-03-07
- 修回日期：2022-06-20
- 网络出版日期：2022-07-14
引用本文 |
施国静, 吴效俭, 王莹莹. 细菌六价铬还原及吸附机制研究进展[J]. 微生物学报, 2022, 62(11): 4287-4304.
Shi Guojing, Wu Xiaojian, Wang Yingying. Mechanism of bacterial reduction and biosorption of hexavalent chromium[J]. Acta Microbiologica Sinica, 2022, 62(11): 4287-4304.
细菌六价铬还原及吸附机制研究进展
1. 南开大学环境科学与工程学院, 天津 300350;
2. 环境污染过程与基准教育部重点实验室, 天津 300350;
3. 天津市城市生态环境修复与污染防治重点实验室, 天津 300350
2. 环境污染过程与基准教育部重点实验室, 天津 300350;
3. 天津市城市生态环境修复与污染防治重点实验室, 天津 300350
摘要：六价铬[Hexavalent chromium，Cr(Ⅵ)]是一种致癌物，其毒性远大于三价铬，因此会对人体健康和生态环境造成危害。Cr(Ⅵ)污染场地中的细菌主要通过生物还原和生物吸附降低Cr(Ⅵ)的毒性和迁移能力。Cr(Ⅵ)还原细菌的抗性机制与还原过程已被多次讨论，但现有综述还缺乏细菌类别、铬酸盐还原酶活性与吸附机制的总结。因此，本文通过系统发育树展示常见Cr(Ⅵ)还原细菌的类别，归纳细菌的Cr(Ⅵ)还原机制，总结现阶段铬酸盐还原酶的酶活性参数与反应条件，并讨论环境影响因子对细菌Cr(Ⅵ)还原的影响。其次，本文综述了细菌对Cr(Ⅵ)的吸附现象与机理。最后，本文对未来细菌修复Cr(Ⅵ)污染的机理研究进行了展望，以期加深对细菌Cr(Ⅵ)还原和吸附过程的了解。
关键词：六价铬还原 Cr(Ⅵ)还原细菌 铬酸盐还原酶 生物吸附
Mechanism of bacterial reduction and biosorption of hexavalent chromium
1. College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China;
2. Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education), Tianjin 300350, China;
3. Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Tianjin 300350, China
2. Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education), Tianjin 300350, China;
3. Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Tianjin 300350, China
Abstract: Hexavalent chromium [Cr(Ⅵ)] is a carcinogen with the toxicity far greater than that of trivalent chromium. The Cr(Ⅵ) discharged by electroplating and tanning have adverse effects on human health and eco-environment. The Cr(Ⅵ) resistance mechanism and reduction process of Cr(Ⅵ)-reducing bacteria have been discussed, whereas there is a lack of summary of the species, chromate reductase activity, and adsorption mechanism of Cr(Ⅵ)-reducing bacteria. In this review, we reviewed the recently reported Cr(Ⅵ)-reducing bacteria via a phylogenetic tree, elaborated the mechanism of Cr(Ⅵ) reduction by bacteria, summarized the enzymatic parameters and reaction conditions of chromate reductase, and expounded the environmental factors affecting the reduction of Cr(Ⅵ) by bacteria. Further, we clarified the adsorption performance and mechanism of Cr(Ⅵ) by bacteria. Finally, we put forward the research prospects on the mechanism of bacterial bioremediation of Cr(Ⅵ) contamination. With this review, we aim to deepen the understanding about the reduction and biosorption processes of Cr(Ⅵ)-reducing bacteria.
Keywords:
reduction of hexavalent chromium Cr(Ⅵ)-reducing bacteria chromate reductase biosorption
铬(chromium，Cr)在自然界中的化合价为−2价到+6价，其中最常见的是六价铬[hexavalent chromium，Cr(Ⅵ)]与三价铬[trivalent chromium，Cr(Ⅲ)][1–2]。Cr(Ⅵ)主要以CrO42−、HCrO4−与Cr2O72−形态存在[3]。Cr(Ⅲ)在酸性条件下以Cr3+形态存在，在中性与碱性条件主要以Cr(OH)3、Cr(OH)4−与Cr(OH)52−形态存在[3]。
Cr(Ⅵ)与Cr(Ⅲ)的毒性差异由铬的化合价与存在形态决定。对于人体而言，Cr(Ⅵ)属于致癌物质，其致癌机制包括氧化应激反应、DNA损伤与基因组不稳定性[4]。相比于可溶性的Cr(Ⅵ)，Cr(Ⅲ)更容易形成沉淀，其毒性会因生物有效性的降低而减小[4–5]，因此Cr(Ⅲ)的毒性远小于Cr(Ⅵ)。而Cr(Ⅲ)的低毒性体现在对DNA造成的损伤上，Cr(Ⅲ)进入细胞后会与S、O及N形成稳定的化学键，进而破坏DNA[6]。但是吡啶甲酸铬与组氨酸铬等Cr(Ⅲ)可作为人体的营养补充剂，提供人体所需要的铬元素有利于治疗糖尿病[7–8]。因此高毒性的Cr(Ⅵ)转化为低毒性的Cr(Ⅲ)是修复Cr(Ⅵ)污染的关键，并且Cr(Ⅵ)来源与污染现状相比于Cr(Ⅲ)更受研究学者的关注。
环境中Cr(Ⅵ)的主要来源是人类活动与地质作用。其中人类活动主要包括电镀、化学制造、印刷、制革与冶金等[9]。地质作用会导致地壳中铬铁矿(FeCr2O4)的氧化，从而释放Cr(Ⅵ)[10]。这些来源可能使得各种环境介质(土壤[11–12]、地下水[13]、地表水[14]等)均受到Cr(Ⅵ)污染。研究显示，意大利坎帕尼亚平原的农田与索洛弗拉河谷由于制革活动受到了Cr(Ⅵ)污染[11]。该地70%的农田土壤与42%的河谷土壤样品中的Cr(Ⅵ)含量超过了当地Cr(Ⅵ)污染限值(2 μg/g)[11]。在水环境方面，伊朗比尔詹德地下水样品中铬的浓度为0.28–132.34 μg/L，16.66%的样品高于世界卫生组织标准(0.05 mg/L)[13]。我国黄土高原地区的络河与杏子河等流域广泛存在Cr(Ⅵ)，罗江上游更是Cr(Ⅵ)的主要分布区[14]。
环境介质中的Cr(Ⅵ)污染会对生态及人体健康造成危害。研究显示，土壤中高浓度的Cr(Ⅵ)具有生态毒性，可干扰植物生长、养分吸收与光合作用[15]。饮用水中的Cr(Ⅵ)可增加人体胃癌患病的风险[16]。空气中的Cr(Ⅵ)颗粒物也是人体呼吸道癌症的潜在致病因素[17]。因此，近年来如何降低Cr(Ⅵ)污染带来的危害受到了众多研究学者的关注。
生物修复法可以通过不同的方式改变铬的形态、降低其流动性与生物可利用性，使铬污染场地恢复生态功能。生物修复Cr(Ⅵ)主要包括超积累植物富集与微生物修复[18]，其修复原理是通过生物源材料与生物有机体对Cr(Ⅵ)进行还原、吸附、矿化与积累[19]。生物还原(bioreduction)可以将高毒性Cr(Ⅵ)还原成低毒性Cr(Ⅲ)，生物吸附(biosorption)可以限制Cr(Ⅵ)的迁移能力[19–20]。生物矿化是微生物将Cr(Ⅵ)转化为不溶性矿物，或将其固定在微生物合成的矿物晶格中[21]。生物矿化常与生物积累相伴发生，例如，细菌可在胞内将Cr(Ⅵ)还原形成Cr(OH)3与Cr2O3晶体，将铬积累在细胞中[22–23]。
生物修复在Cr(Ⅵ)污染环境修复中具有明显的优势。Cr(Ⅵ)还原细菌(Cr(Ⅵ)-reducing bacteria，CRB)分布广泛，与真菌及藻类相比抗性较强且修复效果显著[24]，可应用于土壤[25]、铬矿尾矿坝[26]与地下水[27]的Cr(Ⅵ)污染修复。根际微生物与植物修复常共同作用于Cr(Ⅵ)污染场地土壤的原位修复[28]。其中具有Cr(Ⅵ)抗性的根际微生物对植物生长有益[29]，并且Cr(Ⅵ)还原细菌使铬毒性降低后，可以促进植物积累Cr(Ⅵ)[30–31]。相比于物理化学修复方法(如反渗透、活性炭吸附与电化学法等)，细菌修复Cr(Ⅵ)污染的成本较低[32–33]，且不易造成污染场地的二次污染[34]。此外，在适合细菌生长的条件下，Cr(Ⅵ)还原细菌可以持续地进行修复[35]。所以生物修复是一种经济、安全与可持续的环境友好型修复方式[19, 33, 36]。
细菌Cr(Ⅵ)还原机理是生物修复领域近5年的研究热点之一。随着研究的推进，越来越多的Cr(Ⅵ)还原细菌被发现[37–39]，我们亟需对Cr(Ⅵ)还原细菌进行系统总结。Cr(Ⅵ)还原细菌可通过还原与吸附作用修复Cr(Ⅵ)污染，其中细菌对Cr(Ⅵ)的还原机制在细胞层面已经较为清晰，但许多文章仅列举铬酸盐还原酶的种类[36, 40–41]，并未汇总铬酸盐还原酶活实验参数。此外，由于吸附作用并非主要的修复机制，较少有文章对细菌吸附过程与机制进行深入讨论与总结[19, 42]。因此本文在Cr(Ⅵ)还原细菌种类的归纳中增加了系统发育分析，对细菌还原过程的酶活性研究及影响因子进行总结分析，对细菌的铬吸附过程进行更深入的总结，结合环境酸碱性对细菌吸附作用进行了展示。本文可加深读者对细菌Cr(Ⅵ)修复过程的理解，为工程菌的选择及还原条件优化提供参考，并对未来的研究方向进行了展望。
1 细菌Cr(Ⅵ)还原 1.1 Cr(Ⅵ)还原细菌多样性Cr(Ⅵ)还原细菌在自然界十分丰富。铬污染场地的土壤中，丰度较高的细菌类群包括酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)、芽单胞菌门(Gemmatimonadetes)与变形杆菌门(Proteobacteria)等[43–44]。本课题组前期通过微生物多样性分析发现，天津子牙经济园区铬浓度最高的土壤样品中，变形杆菌门、芽单孢菌门以及酸杆菌门细菌的相对丰度也较高[12, 45]。在属水平上，相对丰度最高的是溶杆菌属(Lysobacter)。有研究表明，溶杆菌(Lysobacter)、黄湿杆菌(Flavihumibacter)、黄溶菌(Flavisolbacter)与交替赤杆菌(Altererythrobacter)的相对丰度与环境中铬的酸溶性(acid-soluble)及可还原组分显著相关[46]。此外，Wang等[47]发现，在原位修复Cr(Ⅵ)污染时，氢噬胞菌属(Hydrogenophaga)、假单胞菌属(Pseudomonas)、微小杆菌属(Exiguobacterium)与红杆菌属(Rhodobacter)在场地中富集并发挥Cr(Ⅵ)还原作用。在铬污染场地丰度较高的细菌类群中，包含了许多Cr(Ⅵ)还原细菌，这些细菌在污染场地的生物修复中起到了重要作用[48–49]。
研究人员已从不同环境中筛选得到了多种Cr(Ⅵ)还原细菌。图 1为近年来报道较多的Cr(Ⅵ)还原细菌16S rRNA基因的系统发育树，这些细菌主要集中在变形杆菌门中的α-、β-、γ-变形杆菌纲、厚壁菌门(Firmicutes)与放线菌门[39]，而在蓝细菌门(Cyanobacteria)与栖热菌门(Deinococcus-Thermus)中分布相对较少。此外，δ-变形杆菌纲中的Geobacter[50]与Desulfovibrio[51]等也是被报道较多的Cr(Ⅵ)还原细菌。
|
| 图 1 Cr(Ⅵ)还原细菌16S rRNA基因系统发育树 Figure 1 Cr(Ⅵ)-reducing bacteria (CRB) 16S rRNA gene phylogenetic tree. The tree was constructed using neighbor-joining, and the circle on the clade represents the bootstrap of 1 000 repetitions. |
研究显示，Cr(Ⅵ)还原作用在不同菌属中普遍存在，归因于铬酸盐抗性基因(chromate resistance genes)[52]和铬酸盐还原酶基因(chromate reductase genes)[53]在细菌间的水平转移[54]。Huang等[55]通过基因挖掘技术发现，同时具有铬抗性基因chrA (Cr-resistant gene chrA；铬酸盐转运蛋白基因)与铬酸盐还原酶基因的物种有41个，其中数量最多的物种依次为产碱杆菌科(Alcaligenaceae)、肠杆菌科(Enterobacteriaceae)与芽孢杆菌科(Bacillaceae)。其中芽孢杆菌是近年来研究较多的Cr(Ⅵ)还原细菌[21, 56–57]，该菌在Cr(VI)胁迫下具有高耐受性与还原能力。细菌金属抗性基因的水平转移常发生在污水处理过程及自然环境中[58–61]，这有助于提高Cr(Ⅵ)胁迫下群落结构的稳定性[62]。
1.2 细菌Cr(Ⅵ)还原机制Cr(Ⅵ)还原细菌分布范围广泛，且对Cr(Ⅵ)污染环境的修复效果显著，其Cr(Ⅵ)还原机制一直是生物修复领域的研究重点[19]。从高效Cr(Ⅵ)还原细菌的筛选，到关键铬酸盐还原酶基因与铬酸盐还原酶的研究，细菌Cr(Ⅵ)还原机制的探索已由现象逐步深入到分子机理[63]。如图 2所示，细菌Cr(Ⅵ)还原机制包括铬酸盐还原酶还原(chromate reductase reduction)与非酶物质还原(non-enzymatic reduction)[64]。铬酸盐还原酶可分为胞内还原酶(intracellular reductase)、胞外还原酶(extracellular reductase)和膜结合还原酶(membrane bound reductase)[40, 42]。由于铬酸盐还原酶并非单独存在于某一细胞组分，不同位点的铬酸盐还原酶在细菌还原过程中均起作用。因此铬酸盐还原酶具有空间位置、还原效果与机制上的差异。而非酶物质还原包括谷胱甘肽、抗坏血酸和半胱氨酸等对Cr(Ⅵ)的还原[65]。此外，来自铁还原菌与硫酸盐还原菌的厌氧代谢产物Fe(Ⅱ)和H2S以及环境中的硫化物与有机质也可以对Cr(Ⅵ)进行还原[2, 66]。铬酸盐还原酶与非酶物质都可以单独对Cr(Ⅵ)进行还原，因此2种还原过程相互影响，均起到Cr(Ⅵ)还原作用。
|
| 图 2 细菌的Cr(Ⅵ)还原机制 Figure 2 Mechanism of Cr(Ⅵ) reduction by bacteria. Chromate reductase includes intracellular reductase, membrane bound reductase and extracellular reductase, among which the common intracellular reductases are ChrR, YieF, NfrA, NfsA and NitR, et al. Non-enzymatic substances includes glutathione, ascorbic acid, cysteine, Fe(Ⅱ) and sulfides, et al. |
细菌胞内还原酶的Cr(Ⅵ)还原作用，普遍高于胞外还原酶和膜结合还原酶的还原作用[67]。例如，Pseudomonas umsongensis CY-1细胞质组分(cytoplasmic fraction)对Cr(Ⅵ)还原作用远高于细胞膜组分(cell envelope fraction)和细胞外组分(extracellular fraction)[35, 68]；Aeribacillus pallidus BK1对Cr(Ⅵ)的还原也主要依赖胞内还原酶进行[69]。根据蛋白质序列的同源性可以将已鉴别出的多种胞内还原酶分为2类[70]：类别一(Class Ⅰ)包括铬酸盐还原酶ChrR/YieF、N-乙基马来酰亚胺还原酶NemA、老黄酶OYE、偶氮还原酶AzoR和硝基还原酶NitR等。类别二(class Ⅱ)大多为硝基还原酶，包括氧不敏感硝基还原酶NfsA/ NfsB、硝基还原酶NfrA和黄素氧化还原酶NfoR等。这些胞内还原酶多以黄素为辅助因子，以NAD(P)H为电子供体对Cr(Ⅵ)进行还原。在细菌Cr(Ⅵ)还原过程中，电子供体NAD(P)H失去氢离子(H+)及电子形成NAD(P)+，失去的电子通过铬酸盐还原酶提供给Cr(Ⅵ)转化为Cr(Ⅲ)[42]。迄今为止，大部分胞内还原酶的结构、Cr(Ⅵ)结合位点及电子传递机理等尚不明确[71]。
目前，胞外还原酶、膜结合还原酶的研究局限于细胞外组分与细胞膜组分中粗酶还原效果的比较。研究显示，胞外还原酶、膜结合还原酶大多与胞内还原酶共同实现还原作用。例如，Shewanella loihica PV-4利用胞内还原酶与胞外还原酶共同还原Cr(Ⅵ)[72]，Bacillus sp. M6则利用胞内还原酶与膜结合还原酶共同还原Cr(Ⅵ)[73]。已知的胞外还原酶与膜结合还原酶较少(图 2)。具有2个跨膜螺旋的Mcr已被鉴定为膜结合还原酶[74]。此外，Cr(Ⅵ)作为唯一电子受体的条件下，Shewanella oneidensis MR-1的外膜细胞色素MtrC与OmcA也是胞外末端还原酶[75]。在细胞外和细胞表面Cr(Ⅵ)还原过程中，细菌可产生纳米导线与电子穿梭体促进胞外电子传递[76]。大部分的细菌的细胞外组分同细胞膜组分均具有Cr(Ⅵ)还原能力，但其中铬酸盐还原酶并没有经过纯化鉴定，因此缺乏蛋白结构与作用机理等相关信息。胞外还原酶和膜结合还原酶仍是未来研究的重点关注对象。
1.3 铬酸盐还原酶活性研究铬酸盐还原酶活性(chromate reductase activity)的检测可以用于分析细菌对Cr(Ⅵ)的还原作用机制[77]，例如，通过对粗酶和纯化的铬酸盐还原酶进行活性检测，可判断细菌Cr(Ⅵ)还原是否为生物作用。虽然铬酸盐还原酶活性的定义不尽相同[63, 77–78]，但基本定义均为“一个单位的酶活性为1 min还原1 nmol Cr(Ⅵ)的酶量”。细菌还原Cr(Ⅵ)的具体位点可以通过不同组分的铬酸盐还原酶活性比较确定[63]。例如，Huang等[65]利用Sporosarcina saromensis W5各组分的粗酶进行Cr(Ⅵ)还原实验发现，胞内还原酶和膜结合还原酶的还原作用比胞外还原酶更强；Elmeihy等[79]利用链酶蛋白酶消化Geobacter sulfurreducens的胞外还原酶，确定了细菌Cr(Ⅵ)还原主要发生在胞外。
迄今为止，铬酸盐还原酶的酶学实验(enzyme assays)数据相对较少。表 1总结了近年来铬酸盐还原酶的酶动力学参数，其中米氏常数Km表示铬酸盐还原酶与Cr(Ⅵ)的亲和力，Km越小则亲和力越强[80]。最大反应速率Vmax代表一定铬酸盐还原酶量下Cr(Ⅵ)饱和的反应速率。多数铬酸盐还原酶对Cr(Ⅵ)的还原不具有专一性，而是行使其他生理功能的同时展现Cr(Ⅵ)还原特性[71]，例如NitR的硝基还原酶活性[77]与YhdA的偶氮还原酶活性[81]等。此外，铬酸盐还原酶还原Cr(Ⅵ)的酶学实验中，基本以NADPH或NADH作为电子供体[82]。
表 1. 铬酸盐还原酶的动力学参数与反应条件
Table 1. Kinetic parameters and reaction conditions of chromate reductase in enzyme assays
| Chromate reductase | Strain | Km/ (μmol/L) |
Vmax/ (μmol/(min∙mg)) |
T/℃ | Time | Electron donor | Buffer (pH) | References |
| NitR | Pannonibacter phragmitetus BB |
14.55 | 34.46 | 35 | 30 min | NADPH | Phosphate buffer (pH 7.0) | [63] |
| GST-EcNfsA | Escherichia coli DH5α |
11.8 | 3.8×10−3 | 55 | 1 h | 1 mmol/L NADH |
10 mmol/L Tris-HCl (pH 7.0) |
[77] |
| GST-EcNfsB | Escherichia coli DH5α |
23.5 | 3.9×10−3 | 30 | 1 h | 1 mmol/L NADH |
10 mmol/L Tris-HCl (pH 7.0) |
[77] |
| GST-VhNfsA | Vibrio harveyi KCTC 2720 |
5.4 | 10.7×10−3 | 30 | 1 h | 1 mmol/L NADH |
10 mmol/L Tris-HCl (pH 7.0) |
[77] |
| NemA | Enterobacter sp. Z1 |
212.1± 63.6 |
37.7±3.9 | Room temperature | 20 min | 1 mmol/L NADPH |
Borate saline buffer | [80] |
| YhdA | Bacillus subtilis |
7 260 | 26.8 | 30 | 30 min | 10 mmol/L NADPH |
100 mmol/L Tris-HCl (pH 7.5) |
[81] |
| ChrR | Pseudomonas putida |
260 | 8.8 | 70 | / | / | 0.05 mol/L citrate buffer(pH 5.0) |
[83] |
| YieF | Escherichia coli |
200 | 5 | 35 | / | / | 0.05 mol/L citrate buffer (pH 5.0) |
[83] |
| NfoR | Staphylococcus aureus LZ-01 |
120.84 | 16.30 | 37 | 5 min | 0.3 mmol/L NADH |
50 mmol/L Tris-HCl buffer (pH 7.0) |
[84] |
| OYE | Thermus scotoductus SA-01 |
3.5/ 8.4 mol/L |
6.2 /16.0 | 65 | 5 min | 0.3 mmol/L NADH/ NADPH |
20 mmol/L MOPS-NaOH buffer, 10 mmol/L CaCl2 (pH 6.5) |
[85] |
| /: not mentioned. | ||||||||
虽然许多具有铬酸盐还原酶活性的蛋白已被报道，但目前我们对铬酸盐还原酶的Cr(Ⅵ)结合位点及还原过程的了解还十分有限。未来需要进一步探究铬酸盐还原酶的结构与功能。
1.4 细菌Cr(Ⅵ)修复过程的影响因子多种环境因子均能影响细菌Cr(Ⅵ)还原与吸附的效果，如pH、温度、Cr(Ⅵ)初始浓度、共存离子与电子供体等[37, 86]。这些环境因子主要以改变铬酸盐酶活性影响Cr(Ⅵ)修复效果，而其中pH可以改变细菌表面与Cr(Ⅵ)之间的静电斥力而影响细菌对铬的吸附。
环境pH可以改变Cr(Ⅵ)吸附作用与细菌生长进而影响细菌Cr(Ⅵ)修复效果。由于Cr(Ⅵ)在pH为1–6时以HCrO4−与Cr2O72−的形态存在，在碱性条件下以CrO42−的形态存在，因此铬酸根始终带负电荷存在于溶液之中。而一般情况下细菌表面呈负电荷，所以当pH升高时细菌表面与Cr(Ⅵ)的静电斥力增强，细菌对Cr(Ⅵ)的吸附作用会减弱[87]。此外，pH的极端变化也会改变细菌的生长，进而影响铬酸盐还原酶活性[86]。研究发现，细菌可以在宽范围的pH条件下生存，其中弱碱性条件更有利于Cr(Ⅵ)的还原效果[88]。例如，在pH为4–10的环境中，Bacillus sp. CRB-7能够生长并且还原Cr(Ⅵ)，其中在pH为7–9时具有较高的生长活性与还原效果[89]。同样的现象也出现在Stenotrophomonas pavanii WY601中[35]。此外，Pannonibacter phragmitetus BB在还原的过程中可以将pH为6.5的培养基调节至pH为8.4，通过产碱来应对Cr(Ⅵ)的胁迫[90]。但也存在一些适宜在酸性条件下进行Cr(Ⅵ)还原的细菌，例如，Pseudomonas brenneri能在pH为1–7的环境中生存，其Cr(Ⅵ)还原的最适pH为6[91]。虽然Cr(Ⅵ)还原细菌的最适酸碱条件具有差异，但pH为6–8是大多数细菌还原Cr(Ⅵ)的最佳条件。
温度是影响铬酸盐还原酶活性的另一个重要因素。大多数细菌的最适生长与Cr(Ⅵ)还原的温度在30–37 ℃之间，这与铬酸盐还原酶的最佳酶活性温度接近。研究显示，铬酸盐还原酶YieF酶活性的最佳温度为35 ℃[83]，YhdA最佳温度为30 ℃[81]。高温与低温均会抑制酶的活性，温度过高会使得铬酸盐还原酶变性[89]。但也存在一些嗜热菌，能够在高温下发挥Cr(Ⅵ)还原作用。例如，Aeribacillus pallidus BK1的最佳生长温度为60 ℃，可耐受的温度甚至达到70 ℃[69]。针对冶金等行业的高温废物处理，此类嗜热Cr(Ⅵ)还原细菌具有较高的应用价值[92]。而低温一般不利于细菌生长[89]，会限制生物吸附剂的产量，降低对Cr(Ⅵ)的吸附量。
Cr(Ⅵ)的初始浓度也会影响细菌的还原作用，这与不同细菌的Cr(Ⅵ)最低抑菌浓度MIC紧密相关[93]。当Cr(Ⅵ)浓度低于最低抑菌浓度时，细菌能保证基本生长活性，从而持续地对Cr(Ⅵ)进行还原[21]：Stenotrophomonas pavanii WY601在达到生长稳定期后，菌株对Cr(Ⅵ)的还原率仍可以进一步提高[35]。Cr(Ⅵ)浓度越高，细菌生长越受抑制，还原效率就越低。Cr(Ⅵ)浓度也会影响细菌的基因表达，包括铬酸盐抗性基因与铬酸盐还原酶基因[94]。研究发现，在100–1 000 mg/L Cr(Ⅵ)的浓度区间中，Pannonibacter phragmitetus BB的铬抗性基因chrA与硝基还原酶基因nitR的相对表达量呈下降趋势[63]。综上，细菌在低浓度Cr(Ⅵ)区间中保持较强的生长活性，其铬酸盐抗性基因与铬酸盐还原基因表达水平较高，Cr(Ⅵ)还原能力增强；高浓度Cr(Ⅵ)条件下，细菌为维持其他生理功能而降低Cr(Ⅵ)还原能力，同时Cr(Ⅵ)对细菌产生毒性作用[23]。
环境中的共存离子也会影响细菌对Cr(Ⅵ)的还原，包括金属离子与无机酸根离子。金属离子的作用主要体现在对细菌生长的影响上。研究发现，Cu2+能促进细菌对Cr(Ⅵ)的还原[95]。Cu2+与黄素氧化还原酶NfoR的非特异性结合，可以促进Cr(Ⅵ)还原中的电子转移[96]。Cu2+除了作为辅酶外，还能够在细胞氧化呼吸系统中协助电子转移[86]。由于许多硝基还原酶具有铬酸盐还原酶活性，硝酸盐离子(NO3−)对Cr(Ⅵ)还原的影响备受关注[97]。研究发现，NO3−浓度提高可促使细菌Pseudomonas aeruginosa G12产生多种还原酶，增强细菌的Cr(Ⅵ)还原能力[98]。共存离子促进细菌对Cr(Ⅵ)的还原，彰显了细菌在复合污染环境修复的优势。
此外，由于Cr(Ⅵ)作为还原过程中的电子受体，研究者也需要考虑电子供体(electron donors)本身对Cr(Ⅵ)的还原作用。不同细菌对电子供体的代谢途径具有差异，因此电子供体对Cr(VI)还原的影响取决于细菌种属。常见的有机电子供体有葡萄糖、果糖、乳糖、乳酸、柠檬酸、甘油、醋酸与NADH/NADPH等[86, 99]。现阶段未发现仅利用无机电子供体的Cr(Ⅵ)还原细菌[100]。但在细菌群落中，无机与有机电子供体可作为联合电子供体(例如H2与CH4[101]、单质硫与有机硫[102])起到共同促进Cr(Ⅵ)还原的作用。细菌群落也可以利用无机电子供体S(0)或Fe(0)，产生挥发性脂肪酸以促进Cr(Ⅵ)还原细菌对Cr(Ⅵ)的还原[103]。具备还原能力的电子供体，可以对Cr(Ⅵ)进行直接还原。例如，LB培养基可以缓慢地还原Cr(Ⅵ)[104]。电子供体还可通过提高菌量促进Cr(Ⅵ)还原效果。本课题组研究发现，在单一有机污染物作为碳源的条件下，Acinetobacter haemolyticus HW-2还原0.7 mg/L的Cr(Ⅵ)需12 h，而添加2%的LB培养基后，还原相同浓度Cr(VI)仅需2 h[105]。因此，在选择最佳的电子供体时，应考虑在最高细菌生物量下进行[86]。
细菌Cr(Ⅵ)还原过程不仅受到以上环境因子的影响，还受到细菌的营养方式、溶解氧和共存有机污染物等因素的影响，未来还需要进一步探究不同影响因子与细菌Cr(Ⅵ)还原的相互关系。
2 细菌Cr(Ⅵ)吸附现象与机理 2.1 细菌对Cr(Ⅵ)的吸附由于细菌对Cr(Ⅵ)的还原作用十分显著，因此现阶段已有研究大多关注细菌的还原过程与机制。而报道相对较少的吸附作用在细菌Cr(Ⅵ)修复中也具有重要意义。生物吸附指具有活性或非活性的生物质表面吸附金属离子的物理化学过程[19]。这一过程并不涉及微生物的能量消耗，无论是活细菌还是死细菌都能实现[19]，因此生物吸附具有成本低、化学成分少的优点[106]。
细菌可以通过菌体、细胞产物与胞外聚合物(EPS)对Cr(Ⅵ)进行吸附[107–108]。例如，阚洪媛等[109]发现Bacillus cereus MZ-11灭活菌株可以对1 600 mg/L的Cr(Ⅵ)保持良好的吸附效果。硫酸盐还原菌降解碳源后产生的硫化物和乙酸盐可诱导金属离子沉淀(FeS2和Cr2S3)，该沉淀物可以对铬进行吸附[110]。细菌胞外聚合物中−OH、−NH及C−O等官能团在吸附过程中起重要作用[111–112]。如表 2所示，许多Cr(Ⅵ)还原细菌也具有Cr(Ⅵ)吸附能力，但多数菌株的吸附作用在微生物修复作用中占比较低[99]。细菌进行固定化后可以提高对Cr(Ⅵ)的吸附作用[113]。此外，细菌也可以通过固定化提高海藻酸钠对Cr(Ⅵ)的吸附量[114]。
在Cr(Ⅵ)污染修复过程中，细菌对Cr(Ⅵ)的吸附作用不可或缺。细菌还原与吸附Cr(Ⅵ)的时间次序和空间差异，与细菌主要的Cr(Ⅵ)还原机制有关。Cr(Ⅵ)的吸附主要发生在细胞表面与胞外聚合物中，也可能发生在相应的还原酶中。当细菌利用胞外还原酶还原时，还原作用与细胞表面及胞外聚合物的吸附作用同时发生，吸附于胞外还原酶的Cr(Ⅵ)进而被还原[86]。此时吸附与还原均在胞外进行。当细菌利用膜结合还原酶还原时，Cr(Ⅵ)吸附在无膜结合还原酶的细胞表面，可被胞外还原酶还原或被固定在细胞表面。吸附在膜结合还原酶表面的Cr(Ⅵ)可进一步被还原。此时吸附作用与膜结合还原酶的还原作用发生在细胞表面及胞外[91]。当细菌利用胞内还原酶还原时，吸附在细胞表面的Cr(Ⅵ)可被转运至细胞内还原。此时，2种作用在不同空间上独立进行[115]。由于细菌的Cr(Ⅵ)还原并非某一种还原酶独立作用，因此吸附作用与还原作用在时间与空间上相对独立[116]。例如，Geobacter sulfurreducens PCA细胞表面的总铬含量与胞内总铬含量分别随时间增加而增加[50]。因此根据Cr(Ⅵ)的浓度变化拟合的动力学模型也通常是2种作用的结果。
2.2 细菌的Cr(Ⅵ)吸附机理细菌Cr(Ⅵ)吸附过程中的物理吸附依靠Cr(Ⅵ)与细菌表面较弱的范德华力，而化学吸附则依靠不可逆的化学键[120]。细菌吸附Cr(Ⅵ)的机理包括络合、沉淀及静电作用[42]。环境pH、细菌表面官能团及细胞壁的主要成分都会影响Cr(Ⅵ)的吸附过程。
环境pH影响细菌对Cr(Ⅵ)的静电吸附。在溶液中，Cr(Ⅵ)主要以带负电的含氧酸根形态存在，因此Cr(Ⅵ)易吸附在细菌表面的正电物质上。培养环境的pH会影响细菌对Cr(Ⅵ)的吸附，当pH较低时，细菌表面质子化后带正电荷，容易吸附HCrO4−与Cr2O72−。例如，胺(−NH−)可质子化成−NH3+，通过静电吸附Cr(Ⅵ)[121]。当pH上升后，细菌表面释放质子带负电，对Cr(Ⅵ)的静电斥力增强，则吸附作用减弱[87]。因此在碱性条件下，OH−与CrO42−存在吸附竞争[87]。
细菌表面的蛋白质与多糖等物质的官能团可以吸附Cr(Ⅵ)[112, 115](表 2)。羟基(−OH)和羧基(−COOH)是吸附Cr(Ⅵ)的常见官能团[86]，可以通过化学结合力与静电作用吸附Cr(Ⅵ)。氨基(−NH2)作为细胞膜中蛋白质、碳水化合物及己糖胺的主要成分，可以通过静电作用与氢键作用吸附Cr(Ⅵ)[42]。
细胞壁成分也会导致Cr(Ⅵ)吸附差异。革兰氏阴性菌表面肽聚糖层外的脂多糖，可作为Cr(Ⅵ)的金属螯合剂[36]；革兰氏阳性菌表面众多的负电荷基团可发挥Cr(Ⅵ)吸附作用，包括硫酸基团、羧基与氨基等[36]。
如图 3所示，细菌表面上存在Cr(Ⅵ)的吸附与Cr(Ⅲ)的沉淀过程[36, 106, 120–121]。在酸性条件下，细胞表面质子化后，H+或−NH3+通过静电吸附Cr(Ⅵ)[121]，羟基与羧基可静电吸附Cr(Ⅲ)[36]，含磷基团(−P=O)也可对Cr(Ⅵ)进行吸附[42]。碱性环境中，Cr(Ⅲ)由离子态沉淀为Cr(OH)3，羟基与羧基可吸附Cr(Ⅵ)[86]，氨基(−NH2+)通过氢键与Cr(Ⅵ)结合[42]，Cr(Ⅵ)与带负电荷的OH−存在吸附竞争[87]。
|
| 图 3 细菌表面Cr(Ⅵ)的吸附与Cr(Ⅲ)的沉淀过程 Figure 3 Adsorption of Cr(Ⅵ) and precipitation of Cr(Ⅲ) on bacterial surface. The three horizontal bars (≡) represent the adsorption of the functional groups with chromium, three dots (…) represent hydrogen binding, and the down arrow (↓) represents the Cr(Ⅲ) precipitation. |
3 总结与展望
细菌修复Cr(Ⅵ)污染主要依靠还原与吸附作用，自然界中的Cr(Ⅵ)还原细菌的种类十分丰富，但均具有相似的还原或吸附机制。还原过程中涉及到细菌的胞内还原酶、胞外还原酶及膜结合还原酶的作用。胞内还原酶还原是细菌Cr(Ⅵ)还原的主要方式；细胞外组分与膜组分也具有Cr(Ⅵ)还原作用，但缺乏相应铬酸盐还原酶种类与结构的信息。环境因子可通过改变细菌的生长活性、相关基因的表达及酶活性来影响细菌的Cr(Ⅵ)还原能力。细菌修复Cr(Ⅵ)以还原作用为主；吸附作用主要涉及铬的络合、沉淀及静电吸引，细菌表面官能团在其中发挥主要作用。
目前，研究者不断深入探索细菌对Cr(Ⅵ)还原与吸附机制，但现阶段的研究仍存在许多问题：(1) 许多研究停留在Cr(Ⅵ)污染修复效果的展示，对还原过程中分子机制与电子转移关注较少；(2) 铬酸盐转运蛋白ChrA及膜结合还原酶的结构尚未得到解析；(3) 细菌的吸附过程多与还原过程相耦合，因此单独研究细菌对Cr(Ⅵ)的吸附是一大难点，许多研究仅依靠官能团种类推测吸附过程。
因此，细菌的Cr(Ⅵ)还原与吸附机制可从以下方面深入探究：(1) 从分子生物学水平上，发掘更多与Cr(Ⅵ)还原过程相关的基因与蛋白，并对铬酸盐还原酶种类进行更加严谨有效的分类。同时探究Cr(Ⅵ)与铬酸盐还原酶的结合位点及电子转移过程，明晰铬酸盐还原酶在还原过程中的作用机制；(2) 利用X-射线晶体衍射法、核磁共振等方法解析铬酸盐转运蛋白ChrA的结构；(3) 利用新的方法与检测手段对吸附微过程进行研究与定量，确定铬在吸附过程中的动态变化。综上所述，未来需要综合利用分子生物学与酶动力学方法探究Cr(Ⅵ)的还原过程，厘清细菌对Cr(Ⅵ)的吸附作用，阐明细菌的Cr(Ⅵ)修复过程。
References
| [1] |
Xu YZ, Qin XN, Liu XH, Zhang NX, Zhou YL. The study of chromium pollution and ecological effects. Environmental Science and Technology, 2002, 25(S1): 8-9.
(in Chinese) 徐衍忠, 秦绪娜, 刘祥红, 张乃香, 周英莲. 铬污染及其生态效应. 环境科学与技术, 2002, 25(S1): 8-9. DOI:10.19672/j.cnki.1003-6504.2002.s1.004 |
| [2] | Liang JL, Huang XM, Yan JW, Li YY, Zhao ZW, Liu YY, Ye JY, Wei YM. A review of the formation of Cr(Ⅵ) via Cr(Ⅲ) oxidation in soils and groundwater. Science of the Total Environment, 2021, 774: 145762. DOI:10.1016/j.scitotenv.2021.145762 |
| [3] | Tang X, Huang Y, Li Y, Wang L, Pei XJ, Zhou D, He P, Hughes SS. Study on detoxification and removal mechanisms of hexavalent chromium by microorganisms. Ecotoxicology and Environmental Safety, 2021, 208: 111699. DOI:10.1016/j.ecoenv.2020.111699 |
| [4] | Chen QY, Murphy A, Sun H, Costa M. Molecular and epigenetic mechanisms of Cr(Ⅵ)-induced carcinogenesis. Toxicology and Applied Pharmacology, 2019, 377: 114636. DOI:10.1016/j.taap.2019.114636 |
| [5] | Viti C, Marchi E, Decorosi F, Giovannetti L. Molecular mechanisms of Cr(Ⅵ) resistance in bacteria and fungi. FEMS Microbiology Reviews, 2014, 38(4): 633-659. DOI:10.1111/1574-6976.12051 |
| [6] | Dhal B, Thatoi HN, Das NN, Pandey BD. Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: a review. Journal of Hazardous Materials, 2013, 250/251: 272-291. DOI:10.1016/j.jhazmat.2013.01.048 |
| [7] | Qi SS, Zheng HX, Jiang H, Yuan LP, Dong LC. Protective effects of chromium picolinate against diabetic-induced renal dysfunction and renal fibrosis in streptozotocin-induced diabetic rats. Biomolecules, 2020, 10(3): 398. DOI:10.3390/biom10030398 |
| [8] | DesMarias TL, Costa M. Mechanisms of chromium-induced toxicity. Current Opinion in Toxicology, 2019, 14: 1-7. DOI:10.1016/j.cotox.2019.05.003 |
| [9] | Ukhurebor KE, Aigbe UO, Onyancha RB, Nwankwo W, Osibote OA, Paumo HK, Ama OM, Adetunji CO, Siloko IU. Effect of hexavalent chromium on the environment and removal techniques: a review. Journal of Environmental Management, 2021, 280: 111809. DOI:10.1016/j.jenvman.2020.111809 |
| [10] | Tumolo M, Ancona V, De Paola D, Losacco D, Campanale C, Massarelli C, Uricchio VF. Chromium pollution in European water, sources, health risk, and remediation strategies: an overview. International Journal of Environmental Research and Public Health, 2020, 17(15): 5438. DOI:10.3390/ijerph17155438 |
| [11] | Caporale AG, Agrelli D, Rodríguez-González P, Adamo P, Alonso JIG. Hexavalent chromium quantification by isotope dilution mass spectrometry in potentially contaminated soils from south Italy. Chemosphere, 2019, 233: 92-100. DOI:10.1016/j.chemosphere.2019.05.212 |
| [12] | Han W, Gao GH, Geng JY, Li Y, Wang YY. Ecological and health risks assessment and spatial distribution of residual heavy metals in the soil of an e-waste circular economy park in Tianjin, China. Chemosphere, 2018, 197: 325-335. DOI:10.1016/j.chemosphere.2018.01.043 |
| [13] | Fallahzadeh RA, Khosravi R, Dehdashti B, Ghahramani E, Omidi F, Adli A, Miri M. Spatial distribution variation and probabilistic risk assessment of exposure to chromium in ground water supplies; a case study in the east of Iran. Food and Chemical Toxicology, 2018, 115: 260-266. DOI:10.1016/j.fct.2018.03.019 |
| [14] | He XD, Li PY. Surface water pollution in the middle Chinese loess plateau with special focus on hexavalent chromium (Cr6+): occurrence, sources and health risks. Exposure and Health, 2020, 12(3): 385-401. DOI:10.1007/s12403-020-00344-x |
| [15] | Shahid M, Shamshad S, Rafiq M, Khalid S, Bibi I, Niazi NK, Dumat C, Rashid MI. Chromium speciation, bioavailability, uptake, toxicity and detoxification in soil-plant system: a review. Chemosphere, 2017, 178: 513-533. DOI:10.1016/j.chemosphere.2017.03.074 |
| [16] | Zhitkovich A. Chromium in drinking water: sources, metabolism, and cancer risks. Chemical Research in Toxicology, 2011, 24(10): 1617-1629. DOI:10.1021/tx200251t |
| [17] | O'Brien TJ, Ceryak S, Patierno SR. Complexities of chromium carcinogenesis: role of cellular response, repair and recovery mechanisms. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, 2003, 533(1/2): 3-36. |
| [18] | Malaviya P, Singh A, Anderson TA. Aquatic phytoremediation strategies for chromium removal. Reviews in Environmental Science and Bio/technology, 2020, 19(4): 897-944. DOI:10.1007/s11157-020-09552-y |
| [19] | Jobby R, Jha P, Yadav AK, Desai N. Biosorption and biotransformation of hexavalent chromium[Cr(Ⅵ)]: a comprehensive review. Chemosphere, 2018, 207: 255-266. DOI:10.1016/j.chemosphere.2018.05.050 |
| [20] | Hou DY, O'Connor D, Igalavithana AD, Alessi DS, Luo J, Tsang DCW, Sparks DL, Yamauchi Y, Rinklebe J, Ok YS. Metal contamination and bioremediation of agricultural soils for food safety and sustainability. Nature Reviews Earth & Environment, 2020, 1(7): 366-381. |
| [21] | Zhao XQ, Tang D, Jiang Y. Effect of the reduction-mineralization synergistic mechanism of Bacillus on the remediation of hexavalent chromium. Science of the Total Environment, 2021, 777: 146190. DOI:10.1016/j.scitotenv.2021.146190 |
| [22] | He C, Zhang BG, Jiang YF, Liu H, Zhao HP. Microbial electrolysis cell produced biogas as sustainable electron donor for microbial chromate reduction. Chemical Engineering Journal, 2021, 403: 126429. DOI:10.1016/j.cej.2020.126429 |
| [23] | Karthik C, Barathi S, Pugazhendhi A, Ramkumar VS, Thi NBD, Arulselvi PI. Evaluation of Cr(Ⅵ) reduction mechanism and removal by Cellulosimicrobium funkei strain AR8, a novel haloalkaliphilic bacterium. Journal of Hazardous Materials, 2017, 333: 42-53. DOI:10.1016/j.jhazmat.2017.03.037 |
| [24] | Guo SY, Xiao CQ, Zhou N, Chi R. Speciation, toxicity, microbial remediation and phytoremediation of soil chromium contamination. Environmental Chemistry Letters, 2021, 19(2): 1413-1431. DOI:10.1007/s10311-020-01114-6 |
| [25] |
Han JJ, Chai LJ, Zhang J, Liang XJ. In-situ remediation of hexavalent chromic-contaminated soil with sulfate-reducing bacteria. Environmental Protection of Chemical Industry, 2020, 40(6): 613-618.
(in Chinese) 韩建均, 柴陆军, 张娟, 梁雪杰. 硫酸盐还原菌原位修复六价铬污染土壤. 化工环保, 2020, 40(6): 613-618. DOI:10.3969/j.issn.1006-1878.2020.06.009 |
| [26] | Bansal N, Coetzee JJ, Chirwa EMN. In situ bioremediation of hexavalent chromium in presence of iron by dried sludge bacteria exposed to high chromium concentration. Ecotoxicology and Environmental Safety, 2019, 172: 281-289. DOI:10.1016/j.ecoenv.2019.01.094 |
| [27] | Song X, Wang Q, Jin P, Chen X, Tang SY, Wei CL, Li K, Ding XY, Tang ZW, Fu H. Enhanced biostimulation coupled with a dynamic groundwater recirculation system for Cr(Ⅵ) removal from groundwater: a field-scale study. Science of the Total Environment, 2021, 772: 145495. DOI:10.1016/j.scitotenv.2021.145495 |
| [28] |
Liu SX, Sun Z, Cao RX. The middle trail of the wastes combined Festuca arundinacea remediation technology in chromium contaminated soil. Journal of Henan University of Engineering: Natural Science Edition, 2018, 30(4): 31-37.
(in Chinese) 刘帅霞, 孙哲, 曹瑞雪. 废弃物联合高羊茅修复铬污染土壤中试实验. 河南工程学院学报: 自然科学版, 2018, 30(4): 31-37. |
| [29] | Nayak AK, Panda SS, Basu A, Dhal NK. Enhancement of toxic Cr(Ⅵ), Fe, and other heavy metals phytoremediation by the synergistic combination of native Bacillus cereus strain and Vetiveria zizanioides L.. International Journal of Phytoremediation, 2018, 20(7): 682-691. DOI:10.1080/15226514.2017.1413332 |
| [30] | Ashraf S, Afzal M, Naveed M, Shahid M, Ahmad Zahir Z. Endophytic bacteria enhance remediation of tannery effluent in constructed wetlands vegetated with Leptochloa fusca. International Journal of Phytoremediation, 2018, 20(2): 121-128. DOI:10.1080/15226514.2017.1337072 |
| [31] | Wang L, Lin H, Dong YB, He YH, Liu CJ. Isolation of vanadium-resistance endophytic bacterium PRE01 from Pteris vittata in stone coal smelting district and characterization for potential use in phytoremediation. Journal of Hazardous Materials, 2018, 341: 1-9. DOI:10.1016/j.jhazmat.2017.07.036 |
| [32] | Peng H, Guo J. Removal of chromium from wastewater by membrane filtration, chemical precipitation, ion exchange, adsorption electrocoagulation, electrochemical reduction, electrodialysis, electrodeionization, photocatalysis and nanotechnology: a review. Environmental Chemistry Letters, 2020, 18(6): 2055-2068. DOI:10.1007/s10311-020-01058-x |
| [33] | Xia SP, Song ZL, Jeyakumar P, Shaheen SM, Rinklebe J, Ok YS, Bolan N, Wang HL. A critical review on bioremediation technologies for Cr(Ⅵ)-contaminated soils and wastewater. Critical Reviews in Environmental Science and Technology, 2019, 49(12): 1027-1078. DOI:10.1080/10643389.2018.1564526 |
| [34] | GracePavithra K, Jaikumar V, Kumar PS, Sundar Rajan P. A review on cleaner strategies for chromium industrial wastewater: present research and future perspective. Journal of Cleaner Production, 2019, 228: 580-593. DOI:10.1016/j.jclepro.2019.04.117 |
| [35] | Liu HJ, Wang YQ, Zhang H, Huang GD, Yang QX, Wang YL. Synchronous detoxification and reduction treatment of tannery sludge using Cr(Ⅵ) resistant bacterial strains. Science of the Total Environment, 2019, 687: 34-40. DOI:10.1016/j.scitotenv.2019.06.093 |
| [36] | Pushkar B, Sevak P, Parab S, Nilkanth N. Chromium pollution and its bioremediation mechanisms in bacteria: a review. Journal of Environmental Management, 2021, 287: 112279. DOI:10.1016/j.jenvman.2021.112279 |
| [37] | Guo SY, Xiao CQ, Zheng YT, Li YZ, Chi R. Removal and potential mechanisms of Cr(Ⅵ) contamination in phosphate mining wasteland by isolated Bacillus megatherium PMW-03. Journal of Cleaner Production, 2021, 322: 129062. DOI:10.1016/j.jclepro.2021.129062 |
| [38] | Das S, Chandra Behera B, Mohapatra RK, Pradhan B, Sudarshan M, Chakraborty A, Thatoi H. Reduction of hexavalent chromium by Exiguobacterium mexicanum isolated from chromite mines soil. Chemosphere, 2021, 282: 131135. DOI:10.1016/j.chemosphere.2021.131135 |
| [39] |
Li D, Zhao YC, Song LY, Yin YJ, Wang YQ, Xu ZH. Advances in molecular mechanism of bacterial reduction of hexavalent chromium. Environmental Science, 2014, 35(4): 1602-1612.
(in Chinese) 李斗, 赵由才, 宋立岩, 尹雅洁, 王洋清, 徐中慧. 六价铬细菌还原的分子机制研究进展. 环境科学, 2014, 35(4): 1602-1612. DOI:10.13227/j.hjkx.2014.04.057 |
| [40] |
Xia X, Li MS, Wu SJ, Wang GJ. Research progress in microbial chromium-transformation and resistance and bioremediation. Microbiology China, 2017, 44(7): 1668-1675.
(in Chinese) 夏险, 李明顺, 武士娟, 王革娇. 微生物铬转化和抗性机制与生物修复研究进展. 微生物学通报, 2017, 44(7): 1668-1675. DOI:10.13344/j.microbiol.china.160949 |
| [41] | Elahi A, Arooj I, Bukhari DA, Rehman A. Successive use of microorganisms to remove chromium from wastewater. Applied Microbiology and Biotechnology, 2020, 104(9): 3729-3743. DOI:10.1007/s00253-020-10533-y |
| [42] | Xia X, Wu SJ, Zhou ZJ, Wang GJ. Microbial Cd(Ⅱ) and Cr(Ⅵ) resistance mechanisms and application in bioremediation. Journal of Hazardous Materials, 2021, 401: 123685. DOI:10.1016/j.jhazmat.2020.123685 |
| [43] | Li DN, Li GH, Zhang DY. Field-scale studies on the change of soil microbial community structure and functions after stabilization at a chromiumcontaminated site. Journal of Hazardous Materials, 2021, 415: 125727. DOI:10.1016/j.jhazmat.2021.125727 |
| [44] | Zhang XP, Gai X, Zhong ZK, Bian FY, Yang CB, Li YF, Wen X. Understanding variations in soil properties and microbial communities in bamboo plantation soils along a chromium pollution gradient. Ecotoxicology and Environmental Safety, 2021, 222: 112507. DOI:10.1016/j.ecoenv.2021.112507 |
| [45] | Wu ZN, Gao GH, Wang YY. Effects of soil properties, heavy metals, and PBDEs on microbial community of e-waste contaminated soil. Ecotoxicology and Environmental Safety, 2019, 180: 705-714. DOI:10.1016/j.ecoenv.2019.05.027 |
| [46] | Zhang SY, Hao XD, Tang JH, Hu J, Deng Y, Xu ML, Zhu P, Tao JM, Liang YL, Yin HQ, Jiang LH, Liu XD, Liu HW. Assessing chromium contamination in red soil: monitoring the migration of fractions and the change of related microorganisms. International Journal of Environmental Research and Public Health, 2020, 17(8): 2835. DOI:10.3390/ijerph17082835 |
| [47] | Wang Q, Song X, Wei CL, Jin P, Chen X, Tang ZW, Li K, Ding XY, Fu H. In situ remediation of Cr(Ⅵ) contaminated groundwater by ZVI-PRB and the corresponding indigenous microbial community responses: a field-scale study. Science of the Total Environment, 2022, 805: 150260. DOI:10.1016/j.scitotenv.2021.150260 |
| [48] | Gupta P, Kumar V, Usmani Z, Rani R, Chandra A. Phosphate solubilization and chromium (Ⅵ) remediation potential of Klebsiella sp. strain CPSB4 isolated from the chromium contaminated agricultural soil. Chemosphere, 2018, 192: 318-327. DOI:10.1016/j.chemosphere.2017.10.164 |
| [49] | Upadhyay N, Vishwakarma K, Singh J, Mishra M, Kumar V, Rani R, Mishra RK, Chauhan DK, Tripathi DK, Sharma S. Tolerance and reduction of chromium(Ⅵ) by Bacillus sp.MNU16 isolated from contaminated coal mining soil. Frontiers in Plant Science, 2017, 8: 778. DOI:10.3389/fpls.2017.00778 |
| [50] | Gong YF, Werth CJ, He YX, Su YM, Zhang YL, Zhou XF. Intracellular versus extracellular accumulation of hexavalent chromium reduction products by Geobacter sulfurreducens PCA. Environmental Pollution, 2018, 240: 485-492. DOI:10.1016/j.envpol.2018.04.046 |
| [51] | Franco LC, Steinbeisser S, Zane GM, Wall JD, Fields MW. Cr(Ⅵ) reduction and physiological toxicity are impacted by resource ratio in Desulfovibrio vulgaris. Applied Microbiology and Biotechnology, 2018, 102(6): 2839-2850. DOI:10.1007/s00253-017-8724-4 |
| [52] | Branco R, Chung AP, Johnston T, Gurel V, Morais P, Zhitkovich A. The chromate-inducible chrBACF operon from the transposable element TnOtChr confers resistance to chromium(Ⅵ) and superoxide. Journal of Bacteriology, 2008, 190(21): 6996-7003. DOI:10.1128/JB.00289-08 |
| [53] | He MY, Li XY, Liu HL, Miller SJ, Wang GJ, Rensing C. Characterization and genomic analysis of a highly chromate resistant and reducing bacterial strain Lysinibacillus fusiformis ZC1. Journal of Hazardous Materials, 2011, 185(2/3): 682-688. |
| [54] | Hernández-Ramírez KC, Reyes-Gallegos RI, Chávez-Jacobo VM, Díaz-Magaña A, Meza-Carmen V, Ramírez-Díaz MI. A plasmid-encoded mobile genetic element from Pseudomonas aeruginosa that confers heavy metal resistance and virulence. Plasmid, 2018, 98: 15-21. DOI:10.1016/j.plasmid.2018.07.003 |
| [55] | Huang YL, Feng H, Lu H, Zeng YH. A thorough survey for Cr-resistant and/or-reducing bacteria identified comprehensive and pivotal taxa. International Biodeterioration & Biodegradation, 2017, 117: 22-30. |
| [56] | Zhu YL, He XY, Xu JL, Fu Z, Wu SY, Ni J, Hu BW. Insight into efficient removal of Cr(Ⅵ) by magnetite immobilized with Lysinibacillus sp.JLT12:mechanism and performance. Chemosphere, 2021, 262: 127901. DOI:10.1016/j.chemosphere.2020.127901 |
| [57] | Wadood HZ, Latif A, Mukhtar H, Javed M, Mukhtar H, Rehman Y. Planktonic cells of Staphylococcus and Bacillus species capable of faster chromium reduction in short incubation times as compared to their biofilms. Arabian Journal of Geosciences, 2021, 14(17): 1-9. |
| [58] | Li AD, Li LG, Zhang T. Exploring antibiotic resistance genes and metal resistance genes in plasmid metagenomes from wastewater treatment plants. Frontiers in Microbiology, 2015, 6: 1025. |
| [59] | Li DC, Gao JF, Dai HH, Wang ZQ, Zhao YF, Cui YC. Higher spreading risk of antibacterial biocide and heavy metal resistance genes than antibiotic resistance genes in aerobic granular sludge. Environmental Research, 2022, 212: 113356. DOI:10.1016/j.envres.2022.113356 |
| [60] | Mindlin S, Petrenko A, Petrova M. Chromium resistance genetic element flanked by XerC/XerD recombination sites and its distribution in environmental and clinical Acinetobacter strains. FEMS Microbiology Letters, 2018, 365(8): fny047. |
| [61] | Abou-Shanab RAI, Van Berkum P, Angle JS. Heavy metal resistance and genotypic analysis of metal resistance genes in Gram-positive and Gram-negative bacteria present in Ni-rich serpentine soil and in the rhizosphere of Alyssum murale. Chemosphere, 2007, 68(2): 360-367. DOI:10.1016/j.chemosphere.2006.12.051 |
| [62] | Jin HJ, Squier TC, Long PE. Dying for good: virusbacterium biofilm co-evolution enhances environmental fitness. Biochemistry Insights, 2012, 5: 1-9. |
| [63] | Chai LY, Ding CL, Tang CJ, Yang WC, Yang ZH, Wang YY, Liao Q, Li JW. Discerning three novel chromate reduce and transport genes of highly efficient Pannonibacter phragmitetus BB: from genome to gene and protein. Ecotoxicology and Environmental Safety, 2018, 162: 139-146. DOI:10.1016/j.ecoenv.2018.06.090 |
| [64] | Thatoi H, Das S, Mishra J, Rath BP, Das N. Bacterial chromate reductase, a potential enzyme for bioremediation of hexavalent chromium: a review. Journal of Environmental Management, 2014, 146: 383-399. DOI:10.1016/j.jenvman.2014.07.014 |
| [65] | Huang YJ, Zeng Q, Hu L, Zhong H, He ZG. Bioreduction performances and mechanisms of Cr(Ⅵ) by Sporosarcina saromensis W5, a novel Cr(Ⅵ)-reducing facultative anaerobic bacteria. Journal of Hazardous Materials, 2021, 413: 125411. DOI:10.1016/j.jhazmat.2021.125411 |
| [66] | Somasundaram V, Philip L, Bhallamudi SM. Experimental and mathematical modeling studies on Cr(Ⅵ) reduction by CRB, SRB and IRB, individually and in combination. Journal of Hazardous Materials, 2009, 172(2/3): 606-617. |
| [67] | Zhu YF, Yan JW, Xia L, Zhang X, Luo LX. Mechanisms of Cr(Ⅵ) reduction by Bacillus sp.CRB-1, a novel Cr(Ⅵ)-reducing bacterium isolated from tannery activated sludge. Ecotoxicology and Environmental Safety, 2019, 186: 109792. DOI:10.1016/j.ecoenv.2019.109792 |
| [68] | Yao Y, Hu L, Li SZ, Zeng Q, Zhong H, He ZG. Exploration on the bioreduction mechanisms of Cr(Ⅵ) and Hg(Ⅱ) by a newly isolated bacterial strain Pseudomonas umsongensis CY-1. Ecotoxicology and Environmental Safety, 2020, 201: 110850. DOI:10.1016/j.ecoenv.2020.110850 |
| [69] | Ma Y, Zhong H, He ZG. Cr(Ⅵ) reductase activity locates in the cytoplasm of Aeribacillus pallidus BK1, a novel Cr(Ⅵ)-reducing thermophile isolated from Tengchong geothermal region, China. Chemical Engineering Journal, 2019, 371: 524-534. DOI:10.1016/j.cej.2019.04.085 |
| [70] | Ackerley DF, Gonzalez CF, Keyhan M, Blake R 2nd, Matin A. Mechanism of chromate reduction by the Escherichia coli protein, NfsA, and the role of different chromate reductases in minimizing oxidative stress during chromate reduction. Environmental Microbiology, 2004, 6(8): 851-860. DOI:10.1111/j.1462-2920.2004.00639.x |
| [71] | O'Neill AG, Beaupre BA, Zheng YZ, Liu DL, Moran GR. foR: chromate reductase or flavin mononucleotide reductase?. Applied and Environmental Microbiology, 2020, 2020(22): e01758-20. |
| [72] | Wang GY, Zhang BG, Li S, Yang M, Yin CC. Simultaneous microbial reduction of vanadium(Ⅴ) and chromium(Ⅵ) by Shewanella loihica PV-4. Bioresource Technology, 2017, 227: 353-358. DOI:10.1016/j.biortech.2016.12.070 |
| [73] | Li MK, He ZG, Hu YT, Hu L, Zhong H. Both cell envelope and cytoplasm were the locations for chromium(Ⅵ) reduction by Bacillus sp.M6. Bioresource Technology, 2019, 273: 130-135. DOI:10.1016/j.biortech.2018.11.006 |
| [74] | Pei YX, Tao C, Ling ZM, Yu ZS, Ji J, Khan A, Mamtimin T, Liu P, Li XK. Exploring novel Cr(Ⅵ) remediation genes for Cr(Ⅵ)-contaminated industrial wastewater treatment by comparative metatranscriptomics and metagenomics. The Science of the Total Environment, 2020, 742: 140435. DOI:10.1016/j.scitotenv.2020.140435 |
| [75] | Belchik SM, Kennedy DW, Dohnalkova AC, Wang YM, Sevinc PC, Wu H, Lin YH, Lu HP, Fredrickson JK, Shi L. Extracellular reduction of hexavalent chromium by cytochromes MtrC and OmcA of Shewanella oneidensis MR-1. Applied and Environmental Microbiology, 2011, 77(12): 4035-4041. DOI:10.1128/AEM.02463-10 |
| [76] | Zhang Q, Amor K, Galer SJG, Thompson I, Porcelli D. Using stable isotope fractionation factors to identify Cr(Ⅵ) reduction pathways: metal-mineral-microbe interactions. Water Research, 2019, 151: 98-109. DOI:10.1016/j.watres.2018.11.088 |
| [77] | Kwak YH, Lee DS, Kim HB. Vibrio harveyi nitroreductase is also a chromate reductase. Applied and Environmental Microbiology, 2003, 69(8): 4390-4395. DOI:10.1128/AEM.69.8.4390-4395.2003 |
| [78] | Gu RJ, Gao JY, Dong LL, Liu Y, Li XL, Bai QH, Jia Y, Xiao H. Chromium metabolism characteristics of coexpression of ChrA and ChrT gene. Ecotoxicology and Environmental Safety, 2020, 204: 111060. DOI:10.1016/j.ecoenv.2020.111060 |
| [79] | Elmeihy R, Shi XC, Tremblay PL, Zhang T. Fast removal of toxic hexavalent chromium from an aqueous solution by high-density Geobacter sulfurreducens. Chemosphere, 2021, 263: 128281. DOI:10.1016/j.chemosphere.2020.128281 |
| [80] | Shi KX, Radhakrishnan M, Dai XL, Rosen BP, Wang GJ. NemA catalyzes trivalent organoarsenical oxidation and is regulated by the trivalent organoarsenical-selective transcriptional repressor NemR. Environmental Science & Technology, 2021, 55(9): 6485-6494. |
| [81] | Valenzuela-García LI, Zapata BL, Ramírez-Ramírez N, Huchin-Mian JP, Robleto EA, Ayala-García VM, Pedraza-Reyes M. Novel biochemical properties and physiological role of the flavin mononucleotide oxidoreductase YhdA from Bacillus subtilis. Applied and Environmental Microbiology, 2020, 86(20): e01688-20. |
| [82] | Huang HY, Tao XY, Jiang YM, Khan A, Wu Q, Yu X, Wu D, Chen Y, Ling ZM, Liu P, Li XK. The naphthalene catabolic protein NahG plays a key role in hexavalent chromium reduction in Pseudomonas brassicacearum LZ-4. Scientific Reports, 2017, 7: 9670. DOI:10.1038/s41598-017-10469-w |
| [83] | Ackerley DF, Gonzalez CF, Park CH, Blake R 2nd, Keyhan M, Matin A. Chromate-reducing properties of soluble flavoproteins from Pseudomonas putida and Escherichia coli. Applied and Environmental Microbiology, 2004, 70(2): 873-882. DOI:10.1128/AEM.70.2.873-882.2004 |
| [84] | Han HW, Ling ZM, Zhou TY, Xu R, He YX, Liu P, Li XK. Copper(Ⅱ) binding of NAD(P)H-flavin oxidoreductase (NfoR) enhances its Cr(Ⅵ)-reducing ability. Scientific Reports, 2017, 7: 15481. DOI:10.1038/s41598-017-15588-y |
| [85] | Opperman DJ, Piater LA, Van Heerden E. A novel chromate reductase from Thermus scotoductus SA-01 related to old yellow enzyme. Journal of Bacteriology, 2008, 190(8): 3076-3082. DOI:10.1128/JB.01766-07 |
| [86] | Tan H, Wang C, Zeng GQ, Luo Y, Li H, Xu H. Bioreduction and biosorption of Cr(Ⅵ) by a novel Bacillus sp. CRB-B1 strain. Journal of Hazardous Materials, 2020, 386: 121628. DOI:10.1016/j.jhazmat.2019.121628 |
| [87] | Yaashikaa PR, Kumar PS, Mohan Babu VP, Durga RK, Manivasagan V, Saranya K, Saravanan A. Modelling on the removal of Cr(Ⅵ) ions from aquatic system using mixed biosorbent (Pseudomonas stutzeri and acid treated Banyan tree bark). Journal of Molecular Liquids, 2019, 276: 362-370. DOI:10.1016/j.molliq.2018.12.004 |
| [88] |
Liu AL, Wu ZG, Jiang X, Zhao MY, Yang ZZ. Isolation, identification and characterization of Cr(Ⅵ) reducing bacterium Microbacterium sp.BD6. Acta Microbiologica Sinica, 2020, 60(1): 95-105.
(in Chinese) 刘爱霖, 吴志国, 江鑫, 赵明源, 杨宗政. Cr(Ⅵ)还原菌Microbacterium sp.BD6的分离鉴定及还原特性. 微生物学报, 2020, 60(1): 95-105. |
| [89] | Wu MH, Li YZ, Li JJ, Wang Y, Xu H, Zhao Y. Bioreduction of hexavalent chromium using a novel strain CRB-7 immobilized on multiple materials. Journal of Hazardous Materials, 2019, 368: 412-420. DOI:10.1016/j.jhazmat.2019.01.059 |
| [90] | Liao Q, Tang JQ, Wang HY, Yang WC, He LX, Wang YY, Yang ZH. Dynamic proteome responses to sequential reduction of Cr(Ⅵ) and adsorption of Pb(Ⅱ) by Pannonibacter phragmitetus BB. Journal of Hazardous Materials, 2020, 386: 121988. DOI:10.1016/j.jhazmat.2019.121988 |
| [91] | Banerjee S, Kamila B, Barman S, Joshi SR, Mandal T, Halder G. Interlining Cr(Ⅵ) remediation mechanism by a novel bacterium Pseudomonas brenneri isolated from coalmine wastewater. Journal of Environmental Management, 2019, 233: 271-282. |
| [92] | Bai YN, Lu YZ, Shen N, Lau TC, Zeng RJ. Investigation of Cr(Ⅵ) reduction potential and mechanism by Caldicellulosiruptor saccharolyticus under glucose fermentation condition. Journal of Hazardous Materials, 2018, 344: 585-592. DOI:10.1016/j.jhazmat.2017.10.059 |
| [93] | Mishra S, Chen SH, Saratale GD, Saratale RG, Romanholo Ferreira LF, Bilal M, Bharagava RN. Reduction of hexavalent chromium by Microbacterium paraoxydans isolated from tannery wastewater and characterization of its reduced products. Journal of Water Process Engineering, 2021, 39: 101748. DOI:10.1016/j.jwpe.2020.101748 |
| [94] | Gong WJ, Wang XR, Zhao HP. Microbial reduction of Cr(Ⅵ) in the presence of Ni, Cu and Zn by bacterial consortium enriched from an electroplating contaminated site. Biodegradation, 2021, 32(6): 711-722. DOI:10.1007/s10532-021-09962-x |
| [95] | Hora A, Shetty VK. Partial purification and characterization of chromate reductase of a novel Ochrobactrum sp.strain Cr-B4. Preparative Biochemistry & Biotechnology, 2015, 45(8): 769-784. |
| [96] | Han HW, Zheng YZ, Zhou TY, Liu P, Li XK. Cu(Ⅱ) nonspecifically binding chromate reductase NfoR promotes Cr(Ⅵ) reduction. Environmental Microbiology, 2021, 23(1): 415-430. DOI:10.1111/1462-2920.15329 |
| [97] | Hu YT, Chen N, Liu T, Feng CP, Ma LL, Chen S, Li M. The mechanism of nitrate-Cr(Ⅵ) reduction mediated by microbial under different initial pHs. Journal of Hazardous Materials, 2020, 393: 122434. DOI:10.1016/j.jhazmat.2020.122434 |
| [98] | An Q, Deng SM, Xu J, Nan HY, Li Z, Song JL. Simultaneous reduction of nitrate and Cr(Ⅵ) by Pseudomonas aeruginosa strain G12 in wastewater. Ecotoxicology and Environmental Safety, 2020, 191: 110001. DOI:10.1016/j.ecoenv.2019.110001 |
| [99] | Zeng Q, Hu YT, Yang YR, Hu L, Zhong H, He ZG. Cell envelop is the key site for Cr(Ⅵ) reduction by Oceanobacillus oncorhynchi W4, a newly isolated Cr(Ⅵ) reducing bacterium. Journal of Hazardous Materials, 2019, 368: 149-155. DOI:10.1016/j.jhazmat.2019.01.031 |
| [100] | Rahman Z, Thomas L. Chemical-assisted microbially mediated chromium (Cr) (Ⅵ) reduction under the influence of various electron donors, redox mediators, and other additives: an outlook on enhanced Cr(Ⅵ) removal. Frontiers in Microbiology, 2021, 11: 619766. DOI:10.3389/fmicb.2020.619766 |
| [101] | He C, Zhang BG, Yan WY, Ding DH, Guo JH. Enhanced microbial chromate reduction using hydrogen and methane as joint electron donors. Journal of Hazardous Materials, 2020, 395: 122684. DOI:10.1016/j.jhazmat.2020.122684 |
| [102] | Zhang BG, Wang ZL, Shi JX, Dong HL. Sulfur-based mixotrophic bio-reduction for efficient removal of chromium(Ⅵ) in groundwater. Geochimica et Cosmochimica Acta, 2020, 268: 296-309. DOI:10.1016/j.gca.2019.10.011 |
| [103] | Shi JX, Zhang BG, Qiu R, Lai CY, Jiang YF, He C, Guo JH. Microbial chromate reduction coupled to anaerobic oxidation of elemental sulfur or zerovalent iron. Environmental Science & Technology, 2019, 53(6): 3198-3207. |
| [104] | 刘爱霖. Microbacterium sp. BD6的Cr(Ⅵ)还原特性、机理及其应用研究. 天津科技大学硕士学位论文, 2019. |
| [105] | 韩伟. 六溴环十二烷在电子垃圾拆解地的污染特征及微生物降解. 南开大学博士学位论文, 2019. |
| [106] | Samuel MS, Selvarajan E, Chidambaram R, Patel H, Brindhadevi K. Clean approach for chromium removal in aqueous environments and role of nanomaterials in bioremediation: present research and future perspective. Chemosphere, 2021, 284: 131368. DOI:10.1016/j.chemosphere.2021.131368 |
| [107] | Kalola V, Desai C. Biosorption of Cr(Ⅵ) by Halomonas sp.DK4, a halotolerant bacterium isolated from chrome electroplating sludge. Environmental Science and Pollution Research, 2020, 27(22): 27330-27344. DOI:10.1007/s11356-019-05942-0 |
| [108] | Polti MA, Amoroso MJ, Abate CM. Intracellular chromium accumulation by Streptomyces sp.MC1. Water, Air, & Soil Pollution, 2011, 214(1/2/3/4): 49-57. |
| [109] |
Kan HY, Yang SX, Sun LL, Yang YW, Tang MZ, Gao Y, Liu ZL, Jia RL. Isolation, identification and adsorption capacity of a strain resistant to lead, zinc and chromium. Microbiology China, 2020, 47(12): 3974-3986.
(in Chinese) 阚洪媛, 杨世鑫, 孙梁伦, 杨月伟, 唐美珍, 高燕, 刘振路, 贾婼兰. 一株耐铅、锌、铬菌株的分离鉴定及其吸附能力. 微生物学通报, 2020, 47(12): 3974-3986. DOI:10.13344/j.microbiol.china.200536 |
| [110] | Gu WZ, Zheng DC, Li DP, Wei CC, Wang X, Yang Q, Tian C, Cui MY. Integrative effect of citrate on Cr(Ⅵ) and total Cr removal using a sulfate-reducing bacteria consortium. Chemosphere, 2021, 279: 130437. DOI:10.1016/j.chemosphere.2021.130437 |
| [111] | Chug R, Mathur S, Kothari SL, Harish, Gour VS. Maximizing EPS production from Pseudomonas aeruginosa and its application in Cr and Ni sequestration. Biochemistry and Biophysics Reports, 2021, 26: 100972. DOI:10.1016/j.bbrep.2021.100972 |
| [112] | Zeng WM, Li F, Wu CC, Yu RL, Wu XL, Shen L, Liu YD, Qiu GZ, Li JK. Role of extracellular polymeric substance (EPS) in toxicity response of soil bacteria Bacillus sp.S3 to multiple heavy metals. Bioprocess and Biosystems Engineering, 2020, 43(1): 153-167. DOI:10.1007/s00449-019-02213-7 |
| [113] | Hora A, Shetty VK. Kinetics of bioreduction of hexavalent chromium by poly vinyl alcohol-alginate immobilized cells of Ochrobactrum sp.Cr-B4 and comparison with free cells. Desalination and Water Treatment, 2016, 57(19): 8981-8989. DOI:10.1080/19443994.2015.1030704 |
| [114] | El-Naggar NEA, El-khateeb AY, Ghoniem AA, El-Hersh MS, Saber WIA. Innovative low-cost biosorption process of Cr6+ by Pseudomonas alcaliphila NEWG-2. Scientific Reports, 2020, 10: 14043. DOI:10.1038/s41598-020-70473-5 |
| [115] | Li MK, Zhuo YT, Hu YT, Li SZ, Hu L, Zhong H, He ZG. Exploration on the bioreduction mechanism of Cr(Ⅵ) by a gram-positive bacterium: Pseudochrobactrum saccharolyticum W1. Ecotoxicology and Environmental Safety, 2019, 184: 109636. DOI:10.1016/j.ecoenv.2019.109636 |
| [116] | Gutiérrez-Corona JF, Romo-Rodríguez P, Santos-Escobar F, Espino-Saldaña AE, Hernández-Escoto H. Microbial interactions with chromium: basic biological processes and applications in environmental biotechnology. World Journal of Microbiology & Biotechnology, 2016, 32(12): 191. |
| [117] | Sun Y, Lan JR, Du YG, Li Z, Liao X, Du DY, Ye HP, Zhang TC, Chen SH. Efficient removal of heavy metals by synergistic actions of microorganisms and waste molasses. Bioresource Technology, 2020, 302: 122797. DOI:10.1016/j.biortech.2020.122797 |
| [118] | Tyagi B, Gupta B, Thakur IS. Biosorption of Cr(Ⅵ) from aqueous solution by extracellular polymeric substances (EPS) produced by Parapedobacter sp.ISTM3 strain isolated from Mawsmai cave, Meghalaya, India. Environmental Research, 2020, 191: 110064. DOI:10.1016/j.envres.2020.110064 |
| [119] | Wu XY, Ren XQ, Owens G, Brunetti G, Zhou J, Yong XY, Wei P, Jia HH. A facultative electroactive chromium(Ⅵ)-reducing bacterium aerobically isolated from a biocathode microbial fuel cell. Frontiers in Microbiology, 2018, 9: 2883. DOI:10.3389/fmicb.2018.02883 |
| [120] | Pakade VE, Tavengwa NT, Madikizela LM. Recent advances in hexavalent chromium removal from aqueous solutions by adsorptive methods. RSC Advances, 2019, 9(45): 26142-26164. DOI:10.1039/C9RA05188K |
| [121] | Ifthikar J, Ibran Shahib I, Jawad A, Gendy EA, Wang SQ, Wu BB, Chen ZQ, Chen ZL. The excursion covered for the elimination of chromate by exploring the coordination mechanisms between chromium species and various functional groups. Coordination Chemistry Reviews, 2021, 437: 213868. DOI:10.1016/j.ccr.2021.213868 |