磁铁矿对奥奈达希瓦氏菌MR-1厌氧还原甲基橙性能的影响

Effect of magnetite on the performance of anaerobic reduction of methyl orange by Shewanella oneidensis MR-1

摘要:

【目的】在微生物对染料的厌氧还原转化过程中，前人研究发现磁铁矿可以作为胞外电子传递介质提高或降低染料的微生物还原速率，这两种截然不同的作用结果背后的作用机制仍亟待阐明。【方法】利用水热法合成磁铁矿，选择甲基橙作为微生物胞外还原的典型偶氮染料，研究磁铁矿对奥奈达希瓦氏菌MR-1厌氧还原甲基橙(methyl orange, MO)的影响。【结果】研究发现磁铁矿对MO的降解表现出明显的浓度依赖性效应：同只添加细菌组相比，低浓度组(20-50 mg/L) MO的脱色效率提高了4.07%-10.64%，而高浓度组(100-200 mg/L)下降了3.92%-18.35%。进一步研究发现磁铁矿浓度变化对MO微生物还原的影响与染料在矿物表面的分配无关，主要体现在影响细胞表面形态、代谢活性和电子传递效率等方面。低浓度组ATP生成量提高了1.08%-7.65%，生成了0.033-0.051 mg/L Fe²⁺，而高浓度组ATP生成量降低了38.74%-60.14%，Fe²⁺浓度增至0.091 mg/L。此外，外源Fe²⁺的实验结果证明Fe²⁺对MO的厌氧还原同样表现出低浓度(0.01-0.02 mg/L)促进，高浓度(＞0.05 mg/L)抑制的影响趋势。【结论】低浓度磁铁矿未影响细菌细胞形态，提高了细胞代谢活性，体系中少量的溶解态Fe²⁺有利于MO微生物还原，而高浓度磁铁矿则表现出相反的影响趋势。本研究为全面理解磁铁矿对胞外电子传递的影响及其在有机污染物还原转化中的应用提供了参考。

Abstract:

[Objective] Studies have discovered that magnetite could be used as an extracellular electron transfer mediator to increase or decrease the microbial reduction rate of dyes. However, the mechanisms underlying these two distinct results remain to be elucidated. [Methods] In this study, magnetite was synthesized by the hydrothermal method and used for the anaerobic reduction of methyl orange (MO), a typical azo dye, by Shewanella oneidensis MR-1. [Results] Magnetite exerted concentration-dependent effects on the degradation of MO. Specifically, low concentrations (20-50 mg/L) of magnetite increased the decolorization efficiency of MO by 4.07%-10.64%, while high concentrations (100-200 mg/L) of magnetite decreased the efficiency by 3.92%-18.35%, compared with the group with only bacteria for degradation. Furthermore, the changes in magnetite concentration affected cell surface morphology, metabolic activity, and electron transfer efficiency rather than the distribution of dyes on the microbial surface in the microbial reduction of MO. Low concentrations of magnetite increased ATP production by 1.08%-7.65% and led to the production of 0.033-0.051 mg/L Fe²⁺, while the high concentrations of magnetite decreased ATP production by 38.74%-60.14% and increased Fe²⁺ concentration to 0.091 mg/L. In addition, exogenous Fe²⁺ showed similar concentration-dependent effects on the anaerobic reduction of MO, i.e., promoting the MO reduction at low concentrations (0.01-0.02 mg/L) and inhibiting the reduction at high concentrations (＞0.05 mg/L). [Conclusion] Low concentrations of magnetite did not affect the bacterial cell morphology and improved the cell metabolic activity. A small amount of dissolved Fe²⁺ in the system favored the reduction of MO by bacteria, whereas high concentrations of magnetite showed an opposite influencing trend. This work enriches our understanding about the effect of magnetite on extracellular electron transfer and its application in the reductive transformation of organic pollutants.