高耐镉细菌Burkholderia sp.DF3-1对镉的吸附特性及机理

Adsorption Characteristics and Mechanism of High Cadmium-tolerant Bacteria Burkholderia sp.DF3-1 to Cadmium

基于前期从重金属矿区污染土壤中分离和鉴定的一株伯克霍尔德氏菌Burkholderia sp.DF3-1,分析其对环境中镉离子(Cd^(2+))的吸附特性。通过测定不同初始浓度、pH及培养时间下菌株对镉离子的去除效率,并利用扫描电镜和透射电镜观察含镉环境对菌体细胞内外形态的影响,以及红外光谱和质粒消除实验测定菌体表面基团和初步测试耐镉基因位置,探讨菌株Burkholderia sp.DF3-1对环境中镉离子的吸附机制。结果表明,该菌株在10 mg/L以下的Cd^(2+)中生长几乎不受影响,在50 mg/L和100 mg/L时生长受限;在培养24 h达到最大生物量,此后有所减少;在pH为5时,去除效率最高。该菌株最高去除效率为83.64%。扫描电镜结果显示Cd^(2+)致使菌体细胞外表粗糙、变形皱缩;透射电镜结果显示Cd^(2+)使菌体细胞膜增厚,遗传物质分散,细胞膜与细胞质界线模糊;红外光谱结果表明,菌体表面主要是-CH_(2)-、酰胺I、-NO_(2)、-COOH、-C-OH和-CO-基团参与了吸附过程;质粒提取与消除实验可知,耐镉基因可能位于遗传物质而不是质粒上。综上所述,耐镉伯克霍尔德氏菌Burkholderia sp.DF3-1对镉离子的吸附作用同时发生在胞内积累和胞外吸附两方面,初始浓度和pH对其吸附能力具有较大影响。

A Burkholderia sp.DF3-1 strain was isolated and identified previously from contaminated soil in heavy metal mining areas.The strain was preserved in the laboratory of Research Group for Banana Industry Technology.The stain has a strong ability to adsorb cadmium ion.Its adsorption characteristics to cadmium ion(Cd^(2+))of the environment were analyzed further in this study.The adsorption characteristics for environmental cadmium ion(Cd^(2+))were further analyzed by multiple ways.The removal efficiency of cadmium ion by the strain was measured under different initial concentrations,pH and cul-ture time.Effects of cadmium on the internal and external morphology of bacterial cells were detected using a scanning elec-tron microscopy(SEM)and a transmission electron microscopy(TEM).The infrared spectroscopy(Fourier transform infrared spectroscopy,FTIR)was used to determine the changes of different groups on bacterial surface.Location of cadmium toler-ance genes was also predicted by plasmid elimination.The results showed that the growth of this strain was not almost af-fected under the initial Cd^(2+)concentration less than10 mg/L.On the contrary,the initial concentrations of 50 mg/L and 100 mg/L inhibited the growth of Burkholderia sp.DF3-1.Maximum biomass was achieved within 24 hours of culture and de-creased in the following tested time points.By analyzing the effects of different pH on the removal efficiency of Burkholderia sp.DF3-1,it was found that the highest removal efficiency was observed at pH 5.The highest removal efficiency was 83.64%.The results of SEM showed that Cd^(2+)treatment caused the surface of the bacterial cells to be rough,deformed and shrunken.The results of TME demonstrated that Cd^(2+)thickened the cell wall and dissolved the bacterial cell membrane.The boundary between cell membrane and cytoplasm was not obvious.The electron microscopy showed that cadmium had a toxic effect on cells.In addition,the results of FTIR showed that the-CH_(2)-,amide I,-NO_(2),-COOH,-C-OH and-CO-groups were involved in the adsorption process of Cd^(2+)on the bacterial surface.After using SDS and sodium benzoate to eliminate plasmids,there was little difference in cadmium resistance of Burkholderia sp.DF3-1,so it was preliminarily speculated that the cadmium resistance gene of Burkholderia sp.DF3-1 was located in genomic DNA and not in the plasmid.Therefore,the adsorption of cadmium ions by Burkholderia sp.DF3-1 occurs in both intracellular accumulation and extracellular adsorption.The initial concentration and pH have a greater impact on its adsorption capacity.The above research results would provide an important reference for the later soil bioremediation.