Abstract:

As an important neutrophilic Fe(II) oxidizing bacteria, Nitrate-reducing Fe(II) oxidizing bacteria have long been considered as a type of microorganisms with broad application prospects in environmental pollution remediation. They are widely distributed in water and soil environments of various salinities, such as freshwater sediments, groundwater, paddy field soils, and coastal sediments. There were studies shown that salinity may have an inhibitory effect on the growth metabolism and ferrous oxidation process of such Fe(II) oxidizing bacteria, but the specific mechanism of action is unclear. In order to further explore the effect of salinity on the growth and metabolism of nitrate-reducing Fe(II) oxidizing bacteria, this study selected Acidovorax sp. BoFeN1 as a model microorganism and a microcosm culture experiment was set up. The salinity of the reaction system was adjusted by NaCl (the mass concentration of NaCl was 0, 15, 35 and 55 g·L⁻¹, respectively). By monitoring the concentration changes of Fe(II) and nitrates during the reaction and characterizing the products by mineralogy, the Fe(II) oxidation and nitrate reduction processes of nitrate-reducing Fe(II) oxidizing bacteria under different salinity conditions were explored. On the basis, a simulation experiment of real seawater (salinity of 34 g·L⁻¹) was further set up to verify the experimental results. The kinetic results of Fe(II) oxidation and nitrate reduction showed that although low concentrations of sodium chloride had little effect, when the NaCl concentration was 3.5 g·L⁻¹ and 5.5 g·L⁻¹, the Fe(II) oxidation and nitrate reduction processes of Acidovorax sp. BoFeN1 will be promoted. Moreover, phase analysis of the reaction end products by SEM, XRD and FTIR showed that salinity will promote the transformation of microbial Fe(II) oxidation mineralization type from lepidocrocite to goethite. Finally, the real seawater verification experiments showed that under the salinity conditions provided by seawater, the Fe(II) oxidation and nitrate reduction capabilities of Acidovorax sp. BoFeN1 increased by 1.2 times and 1.3 times respectively; at this time, the mineralization types of microbial Fe(II) oxidation were lepidocrocite and goethite. This experimental result is consistent with the conclusion of the microcosm culture experiment. From an environmental point of view, this study proves that nitrate-reducing Fe(II) oxidizing bacteria can adapt to high-salt soil pollution environments such as seawater intrusion, and updates the traditional understanding that salinity inhibits bacterial metabolism. This will help promote the application of such bacteria in the remediation of high-salt environmental pollution.

Key words: salinity, nitrate-reducing Fe(II)-oxidizing bacteria, ferrous oxidation, nitrate reduction, iron cycle

摘要：

作为重要的嗜中性铁氧化菌，硝酸盐还原型铁氧化菌一直以来都被认为是在环境污染修复中具有广阔应用前景的一类微生物，其广泛分布于淡水沉积物、地下水、稻田土壤、海岸沉积物等各种盐度的水土环境中。已有研究指示，盐度可能会对此类铁氧化菌的生长代谢和亚铁氧化过程产生抑制作用，但是具体作用机制尚不清楚。为深入探究盐度对硝酸盐还原型铁氧化菌生长代谢的影响，选取Acidovorax sp. BoFeN1为模式菌株，设置微宇宙培养实验，并利用NaCl调节反应体系盐度（NaCl质量浓度分别为0、15、35、55 g·L⁻¹）。通过监测反应过程中亚铁离子和硝酸盐的浓度变化，并对产物进行矿物学表征，探究硝酸盐还原型铁氧化菌在不同盐度条件下亚铁氧化和硝酸盐还原过程；进一步设置真实海水（盐度为34 g·L⁻¹）的模拟实验对实验结果进行验证。亚铁氧化和硝酸盐还原动力学结果表明，尽管低浓度氯化钠影响不大，但当NaCl质量浓度为35 g·L⁻¹和55 g·L⁻¹时，Acidovorax sp. BoFeN1的亚铁氧化和硝酸盐还原过程会被促进。利用SEM、XRD和FTIR对反应终点产物进行物相分析，结果显示盐度会促进微生物亚铁氧化成矿类型由纤铁矿向针铁矿转变。最后，真实海水验证实验表明，在海水提供的盐度条件下Acidovorax sp. BoFeN1的亚铁氧化和硝酸盐还原能力分别提升了1.2倍和1.3倍；此时，微生物亚铁氧化的成矿类型为纤铁矿和针铁矿。这一结果与微宇宙培养实验所得结论一致。从环境意义上看，该研究证明了硝酸盐还原型铁氧化菌能够适应海水入侵等高盐水土污染环境，更新了盐度抑制细菌代谢的传统认识，这将有助于推动此类细菌在高盐环境污染修复中的应用。

关键词: 盐度, 硝酸盐还原型铁氧化菌, 亚铁氧化, 硝酸盐还原, 铁循环