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锑(Sb)是自然界中存在的一种有毒重金属。长期接触Sb可导致严重的健康问题,如引起人体肝脏、皮肤、呼吸系统和心血管系统疾病。因此,Sb被美国和欧盟列为优先控制污染物[1]。我国是世界上最大的Sb生产国,全球超过80%的Sb供应量来自中国西南部的矿山[2]。环境中Sb既可以通过自然过程,如岩石风化、热液喷发等产生,也可以通过人为活动,如矿山开采、化石燃料燃烧、地下水抽取等过程产生[3]。在Sb高污染地区,Sb负荷超过土壤的自然衰减能力,故导致Sb在谷物和蔬菜中积累,进而沿食物链富集,对人类健康构成巨大的威胁。有研究者发现,Sb矿区附近居民膳食中Sb摄入量是健康标准(360 μg·d−1)的1.5倍[4]。严峻的Sb污染形势,促使全球开始关注Sb的生物地球化学过程[5]。
Sb的化学形态决定了它的毒性、生物利用度和环境迁移性[6]。在自然环境中,Sb主要有2种无机形态,在含氧环境中以五价锑酸盐[Sb(Ⅴ)]为主要形态,而在缺氧条件下主要以毒性较大的三价亚锑酸盐[Sb(Ⅲ)]形式存在[7]。在使用O2作为电子受体的自然环境条件下,Sb的氧化是极其缓慢的,而微生物介导的酶促反应在Sb的形态转化中起着重要的作用[8]。Sb氧化细菌(SbOB)编码的锑氧化酶能够催化Sb(Ⅲ)向Sb(Ⅴ)的转化,以降低Sb的毒性,从而为Sb污染环境的生物修复提供了基础[9]。
近年来,微生物参与的Sb的生物地球化学循化及其介导Sb在固液界面之间的迁移转化引起了较多关注。生物吸附是Sb与微生物复杂的相互作用过程的第一步。大多数微生物表面含有多种带负电荷的基团,如羧基、氨基、羟基,这些基团通过络合、静电吸引和离子交换等作用方式吸附和固定包括Sb在内的多种重金属[10]。菌体表面的吸附作用能显著影响土壤中溶解离子的迁移和转化。另一方面,大多数土壤微生物会附着在含铁、锰、铝氧化物的天然黏土矿物上,形成的微生物—矿物复合物成为土壤中Sb的重要吸附剂[11]。目前,较多研究集中在锑氧化菌的筛选鉴定和分子机理的探究。虽然已经分离出了一些SbOB,但受到Sb耐受性或氧化效率的限制,关于SbOB在Sb污染土壤中对Sb迁移转化的影响机制有待阐明[12]。因此,本研究的目的是:1)从Sb污染土壤中分离和鉴定新的高效SbOB;2)阐释SbOB对污染土壤中Sb的存在形态以及迁移转化的影响。
高效锑氧化菌的筛选鉴定及其对土壤中锑迁移转化的影响
Isolation and identification of a high efficiency antimony oxidizing bacterium and its effect on the migration and transformation of antimony in soil
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摘要: 为了筛选出高抗性的锑(Antimony, Sb)氧化菌株,并阐释该细菌对土壤中Sb迁移转化的机制,从Sb污染土壤中富集培养并分离出Sb高抗性和高氧化效率的菌株,结合细菌形态、生理生化检测、16S rDNA基因序列分析等方法,确定了菌株的分类地位;通过该细菌与Sb污染土壤共孵育实验,研究了细菌对土壤中Sb迁移转化的影响。结果表明,筛选得到的菌株为假单胞菌属Pseμdomonas,命名为Pseμdomonas sp. ZLX16;菌株ZLX16能够耐受2 mol·m−3的Sb(III)以及10 mol·m−3的Sb(V),并且在3 d内可以将100 mmol·m−3 的Sb(Ⅲ)完全氧化。土壤孵育实验表明,该菌株能够显著减少Sb从固相土壤到液相中的释放量达63.5%,对土壤颗粒表面的Sb(III)有氧化作用,并且能够促进Sb(V)以强吸附态的形式固定在土壤中;该菌株对Sb的氧化速率较快,并且可以显著降低土壤中Sb的流动性,对修复Sb矿区污染土壤具有潜在的应用价值。本研究结果可为了解微生物影响土壤中污染物的迁移转化机制提供参考。Abstract: The purpose of this study was to isolate a highly efficient antimonite oxidizing strain and explore the mechanism of this strain’s the migration and transformation of antimony in soil. The taxonomic status of strain was determined by the morphological, physiological and biochemical identification, and 16S rDNA sequence analysis. The strain was incubated with Sb-contaminated soil to explore its effect on Sb mobility. The result suggested that the strain belonged to genus Pseμdomonas, named Pseμdomonas sp. ZLX16. It could tolerate 2 mol·m−3 Sb(III) and 10 mol·m−3 Sb(V). The oxidation experiment results showed that strain oxidized almost 100 mmol·m−3 Sb(Ⅲ) to Sb(V) for 3 d. Soil incubation experiment suggested that strain ZLX16 decreased the Sb release from solid to liquid phase by 63.5%. Strain oxidized adsorbed Sb(III) on the surface of soil and promoted the fixation of Sb(V) in soil in the form of strongly adsorbed Sb. Strain ZLX16 had a high oxidation rate of Sb and could significantly inhibit Sb release from soil to water. The results of this study can provide a reference for understanding the migration and transformation mechanism of microorganisms affecting pollutants in soil.
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表 1 土壤中金属元素的质量分数
Table 1. Mass fraction of metal elements in soil
mg·kg−1 Sb As Fe Mn Ca Mg Al 1 677 409 10 278 98 35 229 1 909 16 688 表 2 Sb土壤中Sb的顺序萃取
Table 2. Sequential extraction of antimony from soil
步骤 萃取剂及萃取条件 萃取形态 1 1×103 mol·m-3 MgCl2,pH=8,2 h,25 ℃ 离子结合态 2 1×103 mol·m-3 NaH2PO4,pH=5,24 h,25 ℃ 强吸附态 表 3 细菌的生理生化特征
Table 3. Physiological and biochemical characteristics of strain
生理生化指标 可利用性 生理生化指标 可利用性 葡萄糖 + 甘露醇 − 果糖 + 接触酶 + 木糖 + M.R. − 蔗糖 − V.P. − 麦芽糖 + 淀粉水解 + 阿拉伯糖 + 苯丙氨酸 − 山梨醇 − 马尿酸盐 − 注:表中“+”表示阳性或者能够利用;“−”表示阴性或者不能利用。 -
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