耐砷芽孢杆菌对As^3+的吸附性能与机制研究

Study on adsorption properties and mechanism of As^3+ by an arsenic-resistant Bacillus strain

为了给砷污染水体的微生物修复提供理想材料和必要的理论依据,从湖南某矿区筛选分离得到一株高耐砷菌株,利用16S rDNA基因测序分析对其进行鉴定.同时,采用单因素试验研究了耐性菌吸附As^3+的影响因素及规律,通过研究等温吸附属性、吸附动力学和热力学属性,分析亚细胞赋存特性,并结合扫描电镜(SEM)、傅里叶红外光谱(FTIR)等技术手段,初步探讨了吸附发生的可能机理.结果表明,通过形态学、生理生化及分子鉴定,初步鉴定为芽孢杆菌属(Bacillus sp.),命名为Bacillus sp. strain AsT4.该菌株固体平板培养对砷的耐受阈值为40 mmol·L^-1;菌株最适生长条件为温度35℃、pH=7.0、NaCl浓度5 g·L^-1、转速180 r·min^-1;芽孢杆菌湿菌体吸附As^3+的优化条件为:温度35℃,溶液pH=6.0,培养时间36 h,As^3+初始浓度10 mg·L^-1,菌量1.5 mL,此条件下的去除率为69.3%.干菌体吸附As^3+的优化条件为:温度35℃,pH=7.0,吸附时间90 min,As^3+初始浓度10 mg·L^-1,投加量0.5 g·L^-1,此条件下的吸附率为72.8%.无论是湿菌体还是干菌体,Langmuir等温吸附模型和拟二级动力学方程能更好地描述耐砷芽孢杆菌AsT4对As^3+的吸附过程,并且是自发、墒增的吸热过程.耐性菌对As^3+的生物吸附和累积以胞内累积和细胞壁富集为主,菌粉表面的羧基、羟基、胺基等活性基团可能在吸附过程中起主要作用.

In order to provide ideal materials and necessary theoretical basis for microbial remediation of arsenic pullution, a high As-resistance strain was isolated from a mining area in Hunan province, and was identified by 16 S rDNA gene sequencing analysis. The influencing factors of As^3+ adsorption by bacterial were studied by single factor experiment. The possible mechanism of adsorption was preliminarily explored by studying adsorption isotherm, kinetics and thermodynamics;the studying of subcellular distribution;and the observation with scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR). The results showed that AsT4 was identified as Bacillus sp. based on the morphological, physiological-biochemical characteristics and molecular identification, and the strain was noted as Bacillus sp. strain AsT4, which can tolerate 40 mmol·L^-1 As^3+ in the solid medium. The optimal growth conditions of strain are 35 ℃, pH=7.0, NaCl 5 g·L^-1 and 180 r·min^-1 of flask rotation. The optimal As^3+ adsorption conditions of wet strain AsT4 are 35 ℃, pH 6.0, cultured time of 36 h, 10 mg·L^-1 of As^3+, 1.5 mL of bacteria, with the adsorption rate was 69.3%;the adsorption rate has reached 72.8% for dry strain under the optimal conditions of 35 ℃, pH 7.0, cultured time of 90 min, 10 mg·L^-1 of As^3+, 0.5 g·L^-1 of dosage. Langmuir model and pseudo-second-order kinetics can better describe the adsorption process of As^3+ by strain AsT4, for both wet or dry strain. The adsorption is an endothermic process of entropy increase, and is spontaneous. The biosorption and accumulation of As^3+ by strain AsT4 were dominated by intracellular accumulation and cell wall enrichment. The hydroxyl group, carbonyl group and amide group on the surface of the bacteria powder may play a major role in the adsorption process.