Abstract:

Addressing the challenge of environmental cadmium (Cd) pollution, microbial adsorption technology has emerged as a promising, cost-effective and eco-friendly method for Cd removal, drawing significant attention. However, the separation and recovery of microbial adsorbents from environmental media remains a challenge. In this regard, magnetotactic bacteria, leveraging their unique magnetotaxis capability, exhibit a promising capacity as recyclable bioadsorbents for Cd removal. Research on utilizing magnetotactic bacteria for Cd(II) removal remains limited, however, with the adsorption mechanisms of these bacteria for Cd(II) not yet fully understood. To address this gap, the model magnetotactic strain Magnetospirillum gryphiswaldense MSR-1 was selected for evaluation in this study. The morphology of MSR-1 before and after Cd(II) adsorption was characterized by utilizing scanning electron microscopy (SEM). Batch adsorption experiments were conducted to investigate the impact of pH, Cd(II) concentrations, microbial biomass and temperature on Cd(II) adsorption efficiency. Kinetic models and adsorption isotherm models were applied to elucidate the adsorption process. Additionally, Fourier transform infrared spectroscopy (FTIR) and sequential elution methods were utilized to delineate the adsorption mechanisms. Our findings revealed that elevated Cd(II) concentrations induced noticeable changes and damage to the surface of MSR-1 cells. Optimal adsorption conditions were determined as a pH of 8.0, a Cd(II) concentration of 1 mg·L⁻¹, a temperature of 30 ℃, an adsorption duration of 1 hour, and a microbial biomass of 3.33 g·L⁻¹ (wet weight), achieving an impressive Cd(II) adsorption efficiency of 87.8%. With increasing Cd(II) concentration from 0.5 to 20 mg·L⁻¹, the adsorption capacity of MSR-1 exhibited a progressive increase, peaking at 1.20 mg·g⁻¹. The adsorption kinetics of MSR-1 towards Cd(II) were accurately described by the pseudo-second-order kinetic model and the Langmuir isotherm model. Notably, functional groups including hydroxyl, amide I and carboxyl groups were involved in the adsorption process. The mechanism in Cd(II) adsorption by MSR-1 mainly includes physical adsorption, ion exchange, complexation and intracellular accumulation, with ion exchange being the dominant process, contributing to 74.9% of the process. In summary, the magnetotactic bacteria MSR-1 exhibits a notable adsorption capacity for Cd(II), providing data support and a theoretical basis for its future potential as a recyclable bioadsorbent material for the bioremediation of Cd-contaminated water and soil.

Key words: magnetotactic bacteria, cadmium, biosorption effect, ion exchange, factors

摘要：

趋磁细菌由于其独有的趋磁运动能力，展现出成为新型可回收生物吸附材料的潜力。但有关趋磁细菌对Cd(Ⅱ) 的吸附去除应用研究仍非常有限，趋磁细菌对Cd(Ⅱ) 的吸附特征与机理尚不明确。选用趋磁细菌模式菌株Magnetospirillum gryphiswaldense MSR-1，采用扫描电子显微镜（SEM）对MSR-1吸附Cd(Ⅱ) 前后的形态进行了表征；通过批吸附实验研究了不同溶液pH值、Cd(Ⅱ) 初始浓度、细菌生物量和温度等反应条件对MSR-1吸附Cd(Ⅱ) 的影响；利用动力学模型、等温吸附模型模拟了吸附过程；采用傅里叶变换红外光谱（FTIR）、顺序洗脱法等方法初步探究了MSR-1对Cd(Ⅱ) 吸附的机理。结果表明，吸附Cd后的MSR-1菌体表面形貌改变并出现破损。MSR-1对Cd(Ⅱ) 的吸附效率主要受pH、初始Cd(Ⅱ) 浓度和细菌生物量等因素影响。当pH为8.0、Cd(Ⅱ) 初始浓度为1 mg·L⁻¹、温度为30 ℃、吸附时间为1 h、细菌生物量（湿质量）为3.33 g·L⁻¹时，MSR-1对Cd(Ⅱ) 的吸附效率可达87.8%。Cd(Ⅱ) 浓度在0.5—20 mg·L⁻¹时，随着Cd(Ⅱ) 浓度的升高，MSR-1对Cd(Ⅱ) 的吸附量逐渐增大，最大吸附量达1.20 mg·g⁻¹。MSR-1对Cd(Ⅱ)的吸附过程遵循准二级动力学方程和Langmuir等温模型。羟基、酰胺I基团和羧基等基团参与了MSR-1吸附Cd(Ⅱ) 的过程。MSR-1对Cd(Ⅱ) 吸附机制可涉及物理吸附、离子交换、络合作用和胞内积累，其中离子交换作用为最主要的吸附机制，贡献占比为74.9%。综上，趋磁细菌MSR-1对Cd(Ⅱ) 有较好的吸附去除能力，为未来作为有潜力的可回收生物吸附材料，用于Cd污染水体和土壤的生物修复提供数据支持和理论依据。

关键词: 趋磁细菌, 镉, 生物吸附作用, 离子交换, 影响因子