扇贝内脏团中耐镉菌株的分离及其吸附镉机理

Isolation and cadmium adsorption mechanisms of cadmium-resistant bacteria strains in digestive gland of scallops

摘要:

为探讨扇贝内脏团中微生态系统与扇贝高能力富集镉（Cd）的关系，从自然环境中采集的栉孔扇贝内脏团中分离、纯化了2株耐Cd细菌（编号为菌株A和B），运用16S rDNA基因序列进行分子鉴定，通过金属吸附实验研究了耐Cd菌株对Cd的吸附能力及其对Cd的吸附特性，并利用扫描电镜、透射电镜相结合的方法研究了Cd胁迫条件下耐镉菌株细胞形态与结构变化，探讨了其对Cd的吸附机理。结果显示，2株菌株（A和B）在固体培养基上能耐受Cd的浓度分别为100和80 mg/L。经16S rDNA测序鉴定菌株A与Nitratireductor sp.亲源关系最近，菌株B与Ruegeria sp.亲源关系最近。2株菌株对Cd的吸附率远高于铜（Cu）、锰（Mn）、锌（Zn）和铅（Pb）等重金属。在50 mg/L Cd浓度的液体培养基中，菌株A、B对Cd富集量分别为48.57和 42.14 mg/g，富集系数分别为971.4和842.8。电镜观察结果显示，经过Cd处理后，2菌株数量均有所减少，细胞中出现空泡，菌株A细胞外沉淀增多，菌株B表面变得粗糙且出现凹陷，表明胞外沉积作用可能是耐Cd菌株对Cd富集作用的重要途径。

关键词:扇贝;镉;耐镉菌株;吸附机理

Abstract:

In order to explore the relationship between the role of bacteria community and the high capacity for accumulation of Cd in the digestive tissues in scallops, two cadmium (Cd)-resistant bacterial strains (named A and B) were isolated from the digestive gland of scallop which were collected from the natural marine environment. Two bacterial strains were classified using 16S rDNA sequence analysis. And the ability of two bacterial strains for the accumulation of Cd and their adsorption characteristics of Cd were researched by the metal adsorption experiments. In addition, the combined technique of scanning electron microscopy (SEM) observation and transmission electron microscopy (TEM) observation was used to observe the cell morphology and inside structure of the bacterial strains under Cd exposure, and the cadmium precipitation and distribution outside and inside the cell were studied to explore the adsorption mechanism of Cd for two bacterial strains. Results showed that the two bacterial strains (A and B) could tolerate Cd²⁺ up to 100 mg/L and 80 mg/L in solid medium respectively. Based on 16S rDNA homology analysis, bacterial A sequences shared high similarities with Nitratireductor sp. and bacterial B was classified as Ruegeria sp. Their adsorption ability of 5 kinds of heavy metal ions (Cd²⁺, Cu²⁺, Mn²⁺, Zn²⁺ and Pb²⁺) were examined and both of them had higher adsorption of Cd than that of other four kinds of metals. In addition, bacterial strain A and B could accumulate Cd to 48.57 mg/g and 42.14 mg/g respectively in 50 mg/L liquid mediums and the accumulation factor for Cd was 971.4 and 842.8 respectively. Scanning electron microscopy (SEM) indicated that the amount of two strains both decreased and empty cavity occurred in some cells after Cd exposure. Obvious Cd precipitates appeared on A strain and more rough surface and irregular convex also appeared on B strain; therefore, extracellular precipitation might be an important way for two bacterial strains to resist and accumulate Cd.

Key words:scallop;cadmium;cadmium-resistant bacteria;adsorption mechanism