Preliminary Study on the Biosorption of Cadmium by Magnetospirillum gryphiswaldense MSR-1
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.
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