w毕业设计（论文）外文文献翻译院 系：厦门理工学院 环境工程年级专业：姓 名：学 号：附 件：Bacterial Sorption of Heavy Metals指导老师评语： 指导教师签名：年 月 日Bacterial Sorption of Heavy Metals Four bacteria, Bacillus cereus, B.subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. Cd and Cu sorption over the concentration range 0.001 to 1 mM was described by Freundlich isotherms. At 1 mM concentrations of both Cd2+ and Cu2+, P. aeruginosa and B. cereus were the most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most efficient at Cd2+ removal and B. subtilis removed the most Cu2+. Removal of Ag+ from solution by bacteria was very efficient; an average of 89% of the total Ag+ was removed from the 1 mM solution, while only 12, 29, and 27% of the total Cd2+, Cu2+, and La3+, respectively, were sorbed from 1 mM solutions. Electron microscopy indicated that La3+ accumulated at the cell surface as needlelike, crystalline precipitates. Silver precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. Neither Cd2+ nor Cu2+ provided enough electron scattering to identify the location of sorption. The affinity series for bacterial removal of these metals decreased in the order Ag La Cu Cd. The results indicate that bacterial cells are capable of binding large quantities of different metals. Adsorption equations may be useful for describing bacterium-metal interactions with metals such as Cd and Cu; however, this approach may not be adequate when precipitation of metals occurs.The fate of toxic metallic cations in the soil environment depends largely on the interactions of these metals with inorganic and organic surfaces. The extent to which a metallic cation interacts with these surfaces determines the concentration of metal in solution and, consequently, the potential for movement into groundwater or uptake by plants. A considerable amount of work has been done to evaluate the adsorption or complexation of various heavy metals by soils (11) and soil constituents, such as clays (22) and organic matter fractions (28). One potentially important organic surface which has received little attention is that of the soil microbial population. Soil microorganisms are typically associated with the clay and organic fractions of the soil microenvironment (21) and would be expected to participate in the metal dynamics typically ascribed to these fractions. Bacteria have a high surface area-to-volume ratio (2) and, as a strictly physical cellular interface, should have a high capacity for sorbing metals from solution. There is evidence that bacterial cells are more efficient at metal removal than clay minerals on a dry-weight basis (31). Kurek and co-workers (17) observed that sorption of Cd2+ by dead cells of a Paracoccus sp. and Serratia marcescens was greater than that of montmorillonite when the solid-to- solution ratio was the same for both bacteria and clay. Live cells accumulated about the same quantity of Cd2+ as did clay.Several investigations have shown that relatively large quantities of metallic cations are complexed by algae (19), bacteria (29), and fungi (20). Metal binding by isolated gram-positive and gram-negative bacterial cell walls has also been evaluated (3, 5, 6, 10, 20). Cell walls of the gram-positive bacteria Bacillus subtilis and B.licheniformis were observed to bind larger quantities of several metals than cell envelopes of the gram-negative bacterium Escherichia coli(3).We are interested in the role of microorganisms in the behavior of various heavy metals in the soil environment. The objectives of this work were to determine the metal-binding capacities of whole cells of two gram-positive and two gram-negative bacteria and to determine whether an equilibrium model, the Freundlich adsorption isotherm, would adequately describe bacterial metal sorption. B.cereus, B.subtilis, and Pseudomonas aeruginosa were examined as representatives of common species frequently isolated from soils. E.coli was also used as a second gram-negative bacterium because it is a well-characterized microorganism and its cell envelope has been shown to bind less metal than do B.subtilis cell walls (3). The four metallic ions used in this investigation were Ag+, Cd2+, Cu2+, and La3+. Cadmium and copper are both toxic cations of environmental importance. Silver and lanthanum, representative of monovalent and trivalent heavy metals, respectively, are also toxic but are less frequently found in the environment.MATERIALS AND METHODSBacteria and growth conditions. The bacteria used in these experiments were B. cereus ATCC 11778; P. aeruginosa ATCC 14886, both obtained from the American Type Culture Collection; B. subtilis 168; and E. coli K-12 strain AB264, both from the Un