华南红壤区水稻土具有含铁量较高、氮元素输入量较大的特性,且部分矿区周边的水稻田受砷污染严重,不仅影响水稻产量,还对食品安全和人类健康造成威胁.利用多轮传代富集的方法,从华南红壤水稻土中纯化获得一株具有硝酸盐还原、亚铁氧化和砷还原功能的贪铜菌Cupriavidus metallidurans Paddy-2.以该细菌为研究对象,探讨纯细菌体系中,硝酸盐还原和亚铁氧化过程对微生物还原As(Ⅴ)的影响,测试了反应体系中As(Ⅴ)和硝酸盐的还原动力学,以及Fe(Ⅱ)的氧化动力学,并对体系中Fe(Ⅱ)氧化所生成的矿物沉淀进行表征分析.As(Ⅴ)还原动力学结果表明,中性厌氧条件下贪铜菌对As(Ⅴ)的还原率为100％,而分别加入硝酸盐和Fe(Ⅱ)均能有效抑制贪铜菌对As(Ⅴ)的还原作用(还原率为27％～49％),两者同时存在对As(Ⅴ)还原的抑制作用最大(还原率只有21％).硝酸盐作为末端电子受体,由于其氧化还原电位比As(Ⅴ)更高,因此比As(Ⅴ)更容易接收电子,从而减缓贪铜菌对As(Ⅴ)的还原效率.Fe(Ⅱ)氧化动力学和矿物表征结果表明,只有在硝酸盐和Fe(Ⅱ)共存的体系里,Fe(Ⅱ)的氧化才能得到有效的促进,并生成含Fe(Ⅲ)的无定形矿物.这些Fe(Ⅲ)矿物覆盖在菌株表面,有可能降低菌株的代谢活性,并有效吸附As(Ⅴ),从而减低体系中As的浓度,达到降低As毒性的效果.研究结果可为受砷污染农田的生物修复技术的开发提供科学依据.%The red paddy soils in South China are with high content of iron and high input of nitrogen.The arsenic contamination in the paddy soils around mining area not only reduces the rice production but also has raised the food safety and human health issue.In this study,Cupriavidus metallidurans Paddy-2 was isolated from the red paddy soil in South China using subculturing technique,which has been identified with the ability of nitrate reduction,ferrous oxidation and arsenate reduction.The objective of this study was to investigate the effects of nitrate reduction and ferrous oxidation on arsenate reduction by C.metallidurans Paddy-2,in which kinetics of As (Ⅴ) reduction,nitrate reduction,and Fe (Ⅱ) oxidation was monitored,and the precipitates after Fe (Ⅱ) oxidation were characterized as well.The results of As (Ⅴ) reduction kinetics revealed that C.metallidurans Paddy-2 could completely reduce the As (Ⅴ) addedat neutral pH under anoxic conditions,whilethe presence of nitrate or Fe (Ⅱ) could inhibit the microbialAs (Ⅴ) reduction with 27％～49％ of As(Ⅴ) reduced.The presence of both nitrate and Fe (Ⅱ) showed the highest inhibition effect on microbial As (Ⅴ) reduction with only 21％ of As (Ⅴ) reduced.Due to the higher redox potential of nitrate than As (Ⅴ),nitrate could serve as a more competitiveelectron acceptorthan As (Ⅴ),and consequently slowed down the microbial As (Ⅴ) reduction rate.The results of Fe (Ⅱ) oxidationkinetics and mineral characterization revealed that only the presence of both Fe (Ⅱ) and nitrate could facilitate the Fe (Ⅱ) oxidation process,resulting in formation of amorphous Fe (Ⅲ) minerals.These minerals were mainly formed on the surface of bacterial cells,probably inhibiting the activity of bacteria,and could effectively adsorbAs (Ⅴ),leading to lower concentration of active arsenic and reduction of arsenic toxicity.The results obtained in this study could provide useful information for the exploration of bio-remediation technology in arsenic-contaminated soils.
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