重金属生物吸附研究中蜡状芽孢杆菌菌体微观形貌的原子力显微镜观察与表征

Application of atomic force microscopy in the characterization of cell morphology of Bacillus Cereus bacteria in the biosorption process of heavy metal ions

对蜡状芽孢杆菌在重金属生物吸附条件下细胞的界面形态及其变化情况进行了原子力显微镜成像观察与表征 .结果表明 ,在严格实验对照条件下未加入Pb(II)的空白菌体细胞呈杆状 ,单个细胞长约 3 3μm ,横截面分析结果为宽 1 9μm左右 ,高为 0 3～ 0 4 μm ,细胞壁表面比较光滑 ,细胞之间以竹节结构首尾相连排列成长杆状 ;吸附Pb(II)后细胞的体积则发生膨胀 ,单个细胞长约 3 9μm ,横截面分析结果为宽 3 1 μm左右 ,高约为 1 1 5 μm ,细胞壁表面变得比较粗糙 ,细胞之间较容易发生粘结 ,与对照空白菌体相比 ,细胞之间呈长杆状的竹节结构排列则变得很少 .采用截面分析曲线中形貌特征的高宽度比R对细菌细胞在云母基底表面的横向铺展变形作用进行了定量表征 (吸附铅离子后R值由 0 1 6 5变为 0 4 1 6 ) ,同时探讨了细胞在基底表面的横向铺展变形作用可能与细胞表面电荷影响细胞在基底表面的粘附性能密切相关 ,并受溶液pH、离子强度以及金属离子的暴露与吸附等外界因素影响而发生改变 .有关其详细机理 。

Atomic force microscopy (AFM) has been used to investigate the morphology of the cell surfaces of Bacillus Cereus in the biosorption process of heavy metal ions. Changes in the cell surface structures including the size, shape and properties of the bacteria under different media conditions and the Pb(Ⅱ) ion exposure as well are probed and characterized through sectional analysis. While newly cultivated Bacillus cereus cells usually have a smooth surface and may have a variety in their cell dimensions from different bacterial colonies, cells after treated in 0.1?mol·L^(-1) HNO_3 or EDTA for overnight become more rough in their cell surface, but remain to preserve the integrity of their cell structure such as the shape and size, implying that the treatment with 0.1?mol·L^(-1) HNO_3 or EDTA does not cause any major change in the cell structure and probably can release only the acidic or binding sites occupied by the metal ions on the cell surface. The morphology of Bacillus Cereus bacteria in the control blank without Pb(Ⅱ) is rod-like in shape with a smooth surface, the size dimension of which is about 3.3?μm in length with a section profile of 1.9?μm in width and 0.3-0.4?μm in height. The bacteria cells are usually found to form a larger rod-like ultra-structure with internal cells connected from end to end. With the Pb(Ⅱ) ion exposure the larger ultra-structures of the bacteria cells are mostly disconnected, and the size dimensions of the bacteria cells are enlarged. The length of the bacteria cells is 3.9?μm, the width and height in the section profile are 3.1?μm and 1.15?μm, respectively. Further more, the surfaces of the bacteria cells are more roughened, and the cells are more likely to adhere to each other randomly. Through the use of section analysis, one interesting phenomenon in the morphological observation of Bacillus Cereus bacteria has been found, i.e. the distortion of section profile in the vertical direction relative to the lateral direction. The cross section shape is far from a circle or a semi-circle, but like an arch. This is attributed to the morphological changes of the soft sample itself when adsorbed onto mica substances, and is believed to be due to the different interaction forces between the bacteria and substrate surfaces, such as the surface charges (both sample and substrate surfaces) in cooperation with internal forces of the bacteria sample etc. This type of change has no range limit and varies quite a lot, depending on sample and surface properties in the particular environment. Nevertheless, it can be characterized by the ratio of vertical vs. lateral distances in the sectional profile, through which the morphological changes of the bacteria cells with Pb(Ⅱ) exposure in relation to the control blank without Pb(Ⅱ) are found, the R value varying from 0.165 to 0.416.