一株耐镉伯克氏菌的分离鉴定及其对镉的吸收转运特性

Isolation and characterization of a cadmium-resistant bacterial strain (Burkholderia cepacia) and its cadmium-absorption and transport properties

农田土壤镉(Cd)污染日益加剧,严重威胁着农村生态安全与居民身体健康,而微生物修复被认为是一种行之有效的Cd污染土壤原位修复方法.为了给Cd污染土壤微生物修复提供功能菌株,采取平板划线从Cd污染土壤中分离纯化得到一株高耐性耐Cd菌株B-6,通过生理生化试验及16S rDNA对其进行了鉴定,并研究了菌株对Cd2+的吸收转运特性.经鉴定,高耐性耐Cd菌株B-6为伯克霍尔德菌属(Burkholderia cepacia),其对Cd2+的耐受阈值为850 mg·L^-1.通过单因素优化培养发现,菌株B-6对Cd2+的吸收量随着培养温度的增加先增大后减小;随着培养液初始pH值的增大先增大后减小,同时发现菌株B-6能够有效调控系统的终点pH值;随着转速的增大先增大后减小.当初始浓度为400 mg·L^-1,培养温度为30℃,培养液初始pH值为5.0,转速为120 r·min^-1,培养时间为72 h时,菌株B-6对Cd2+的吸收效果最佳,达到51 mg·g^-1.通过分析亚细胞组分Cd2+含量发现,Cd2+被菌体吸收后主要赋存于细胞壁.

Cadmium pollution in farmland soil is increasing and seriously threatens rural ecological security and residents′ health. Microbial remediation is considered to be an effective method for in situ remediation of the cadmium contaminated soils. In order for bioremediation of the cadmium-contaminated soil, a highly cadmium-resistant bacterial strain was isolated and purified from the cadmium-contaminated soil by physiological, biochemical tests and 16 S rDNA analysis. The cadmium-absorption and transport properties of the bacterial strain were characterized. The highly cadmium-resistant strain was identified as Burkholderia cepacia B-6 and its tolerance threshold to cadmium was 850 mg·L^-1. Through the single-factor optimization, it was found that the cadmium uptake by the strain B-6 significantly increased first and then decreased with the increase of cultivation temperature. As the initial pH value of the culture solution increased, the pH of the culture system first increased, then decreased, and the strain B-6 could effectively regulate the end-point pH of the culture. With the increase of the flask-shaking speed, the cadmium absorption of the strain B-6 also first increased and then decreased. When the initial concentration of the cadmium in the culture solution was 400 mg·L^-1, the incubation temperature was 30 ℃, the initial pH was 5.0, the rotating speed was 120 r·min^-1, and the incubation time was 72 h, the absorption capacity of Cd2+ by the strain B-6 obtained the maximum at 51 mg·g^-1. The analysis of Cd2+ content distribution in the cell demonstrated that Cd2+ mainly distributed in the cell wall after it was absorbed by the strain B-6. Clearly, the burkholderia cepacia B-6 is an excellent candidate bacterial strain for microbial remediation of the cadmium-contaminated soil.