細菌吸附重金屬外文翻譯

1、<p><b>　　中文5730字</b></p><p>　　畢業(yè)設計（論文）外文文獻翻譯</p><p>　　Bacterial Sorption of Heavy Metals</p><p>　　MD Mullen, DC Wolf, FG Ferris</p><p>　　出處：Appl. Envir

2、on. Microbiol, 1989 - p3143-3149</p><p>　　Four bacteria, Bacillus cereus, B.subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solu

3、tion 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

4、 most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most ef</p><p>　　The fate of toxic metallic cations in the soil environment depends largely on the

5、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

6、 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, su</p><p>　

7、　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

8、 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-n

9、egative bacterium Escherichia coli(3).</p><p>　　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

10、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

11、 sorption. B.cereus, B.subtilis, and Pseudomonas aeruginosa were examined as representatives of common species frequently</p><p>　　MATERIALS AND METHODS</p><p>　　Bacteria and growth conditions.

12、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 Universit

13、y of Guelph. The bacteria were routinely cultured in 0.5x brain heart infusion broth (BBL Microbiology Systems) amended with 2.4 g of HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) liter-1 and 2.0 g of M

14、ES (2-N-morpholinoethanesulfonic</p><p>　　Metal sorption studies. The four metal salts used in this study were AgNO3，Cd(NO3)2·4H2O，Cu(NO3)2·2.5H2O and La(NO3)2·6H2O. The metal solutions were a

15、djusted to pH 4.0 with 0.5 M HNO3 to avoid precipitation of Cu as CuCO3. Identification of these metals in solution at pH 4.0 was done with the GEOCHEM computer program (27). At pH 4.0 in a Ca(NO3)2 matrix, these metalli

16、c cations were predicted to be found primarily in the free ionic form (>97% in all cases).</p><p>　　All of the plasticware used in these studies was leached in 3 M HNO3 and rinsed several times with doub

17、le-deionized water before use to avoid metal contamination. A batch equilibration method was used to determine sorption of metals by bacteria. Two milliliters of washed cells was placed in a 10-ml polypropylene centrifug

18、e tube containing 6 ml of cold 10 mM Ca(NO3)2; and 1 ml of metal stock solution was added. The tubes were capped, placed on an inverting shaker, and equilibrated for 2 h at 5°C.</p><p>　　The sorption ex

19、periment was set up as an unbalanced four-by-four lattice with three replications over time (8). Each block within replicates contained four different bacterium-metal combinations at all four metal concentrations. When a

20、ppropriate, the sorption isotherms were constructed by the methods outlined by Dao et al. (9) with the GLM procedure of the SAS statistical program (25). </p><p>　　Electron microscopy. Electron microscopy wa

21、s done to visualize the location of metals on the bacterial cells. Cells were equilibrated with 1 mM metal solutions as described above and fixed for 30 min at room temperature in 5% glutaraldehyde (EM grade; Polyscience

22、s Inc.) containing the metal of interest at a concentration approximately equal to the equilibration concentration. The cells were then washed free of glutaraldehyde with the metal solution, enrobed in 2% Noble agar (Dif

23、co Laboratories),</p><p>　　Affinity series determination. To further elucidate the affinity of the bacterial cells for these metals, the cells were equilibrated for 2 h at 5°C in solutions containing ei

24、ther the single metal at an initial concentration of 1 mM or all four metals at 1 mM each. As described above, all metal solutions were made in pH 4.0 10 mM Ca(NO3)2. After the cells were harvested by centrifugation, met

25、als in the supernatant were determined by inductively coupled argon plasma spectroscopy. The experiment w</p><p><b>　　RESULTS</b></p><p>　　Bacterial sorption of Cd2+ and Cu2+ from so

26、lution was described well by the linearized Freundlich adsorption isotherm equation,</p><p>　　log10S = log1OK + nlog1OC,</p><p>　　where S is the amount of metal adsorbed in micromoles per gram,

27、C is the equilibrium solution concentration in micromoles per liter, and K and n are Freundlich constants. The Freundlich constants for Cd2+ and Cu2+ sorption by the four bacteria are given in Table 1. The constant K rep

28、resents the predicted quantity of metal removed in micromoles of metal per gram of dry cells at an equilibrium concentration of 1 uM, and n is the slope of the isotherm. Examination of K values for Cd sorption showed<

29、/p><p>　　Freundlich isotherms were not useful for describing the removal of Ag+ and La3+ from solution because there were too few datum points over a wide range of concentrations. Equilibrium concentrations of

30、La3+ were below detection limits when the initial concentration was 10 uM. Several of the observations for Ag+ equilibrium concentrations were also below detection limits at the 10 uM concentration. When the equilibrium

31、concentration was below detection limits, the total metal bound on a dry-weight</p><p>　　Significant differences among the bacteria for La3+ removal were found in the 1 mM treatment when 33, 70, 114, and 144

32、 p.mol g-1 were removed by B.cereus, E. coli, B.subtilis, P.aeruginosa, respectively (Fig.3). There were no significant differences among bacteria for La3+ removal from the 10 or 100 uM solutions. The bacterial cells wer

33、e evidently saturated with La at the 1 mM concentration, as very little additional La3+ was bound by these cells from the 10 mM La3+ treatment (Fig. 3).</p><p>　　Silver was removed from solution much more ef

34、ficiently than were the other metals at the 1 and 0.1 mM concentrations (Table 2). An average of 99% of the total Ag+ was removed from solution in the 0.1 mM treatment. Cadmium was bound by the cells to a much lesser ext

35、ent, with only 12 and 23% of the total Cd2+ removed from the 1 and 0.1 mM treatments, respectively. Even in the 0.001 mM treatment, an average of 46% of the added Cd2+ remained in solution (data not shown).</p>&l

36、t;p>　　Electron micrographs of metal-treated cells showed that Ag was associated with the cell primarily as discrete particles at or near the cell walls of the bacteria, whether they were gram positive or gram negative

37、 (Fig. 4). Energy-dispersive X-ray analysis confirmed that the particles were silver. Attempts were also made to identify the form of silver in the particles by using select-area electron diffraction; however, the partic

38、les were too small to produce useful transforms. Lanthanum was also e</p><p>　　Neither Cu2+ nor Cd2+ provided enough electron scattering to positively identify sites of deposition. Both metals were evidently

39、 diffusely scattered throughout the cell walls of the bacteria. Energy-dispersive X-ray analysis indicated that Cu was present mostly in the cell walls, although small amounts were also detected in the cytoplasm. Cadmium

40、 was bound in such low quantities that none was detected in thin sections. Potassium was a constant element detected in all cells, and one of the K line</p><p>　　The affinity of the bacterial cells for these

41、 cations at the 1 mM concentration decreased in the order Ag+ > La3+ >Cu2+ > Cd2+. When cells were equilibrated with the metals individually, sorptions of Cu2+ and La3+ were essentially equal. However, when cell

42、s were equilibrated with a mixture of all four metals, La3+ sorption always exceeded Cu2+ sorption (Table 3). Binding of each of the metals was reduced when the other cations were present, indicating some competition for

43、 metal-binding sites on </p><p>　　DISCUSSION</p><p>　　The objective of this research was to evaluate the metal sorption capacities of selected gram-positive and gramnegative bacteria and to dete

44、rmine whether Freundlich adsorption isotherms might be useful for evaluating bacterial metal binding. Although adsorption isotherms have been traditionally used to describe stoichiometric solute-solid interactions, such

45、as adsorption, chemisorption, and ion exchange, they have also been used to describe the removal of various cations from a range of solution</p><p>　　We believe that Freundlich isotherms described sorption o

46、f cadmium and copper accurately. Differences in the sorption capacities for cadmium and copper were predicted among the bacteria; however, these differences were relatively small, particularly at low concentrations. The

47、gramnegative bacteria, particularly E. coli, removed more cadmium from solution at low concentrations, as predicted by the Freundlich K constants.</p><p>　　No generalizations regarding differences between gr

48、am-negative and gram-positive bacteria for copper sorption can be made on the basis of our work. At an equilibrium concentration of 1 uM, only a 1.9-fold difference in predicted copper sorption was observed between the m

49、ost and least efficient bacteria, B. subtilis and B. cereus. At higher concentrations, the most efficient bacterium for copper sorption was P.aeruginosa.</p><p>　　The minute differences between gram-positive

50、 and gram-negative bacteria are in contrast to observations of metal binding by isolated cell walls and envelopes of these bacterial groups. Beveridge and Fyfe (3) reported that cell walls of B. subtilis and B. lichenifo

51、rmis bound 28 to 33 times more Cu2+ than did E. coli envelopes. At the same time, their B.subtilis wall preparations complexed much more copper on a mole-to-dry-weight basis than did those used in the whole-cell experime

52、nts reported her</p><p>　　In addition to the metal-to-mass considerations, it is possible that some surface-bound metal was sloughed off together with soluble wall polymer as wall turnover and autolysis prog

53、ressed. Although metal-binding experiments were conducted at low temperatures and toxic-metal concentrations, some metabolic processes, such as wall turn-over, would proceed until all autolytic enzymes had been denatured

54、. The sloughed-off metal-wall polymer would be soluble and free of the bacteria; this complexed met</p><p><b>　　細菌吸附重金屬</b></p><p>　　對蠟狀芽孢桿菌，枯草桿菌，大腸桿菌，綠膿桿菌四種細菌，通過批量平衡方法從溶液中去除Ag+，Cd2+

55、，Cu2+，和La3+的能力進行研究。鎘和銅吸附濃度范圍在0.001到1毫摩爾每升（mmol/L），通過Freundlich等溫線被描述。在Cd2+的和Cu2+的濃度均為1毫摩爾每升時，在金屬去除上綠膿桿菌和蠟狀芽孢桿菌分別是最有效和最無效的細菌。Freundlich K常數表明，在Cd2+的去除上大腸桿菌最有效的和Cu2+的去除上枯草芽孢桿菌最有效的。用細菌從溶液去除Ag+是非常有效的；從1毫摩爾每升的溶液中平均89％的總Ag+被去除

56、，而只有12％的總Cd2+，29％的總Cu2+，和27％的總La3+，分別從1毫摩爾每升的溶液中被吸附。電子顯微鏡觀察表明，La3+沉積在細胞表面上如針狀，析出結晶。在細胞表面上，偶爾在細胞質中銀沉淀如離散的膠狀聚集體。無論Cd2+還是Cu2+都不能提供足夠的電子散射，以確定吸附的位置。細菌清除這些金屬的親和力序列下降順序為Ag> La> Cu > Cd。結果表明，細菌細胞能夠結合大量不同的金屬。吸附方程可用于描述細菌

57、金屬如鎘、銅等金屬的相互作用，但是，當金</p><p>　　在土壤環(huán)境中的有毒金屬離子的結局在很大程度上取決于這些金屬離子與無機和有機表面的相互作用。金屬陽離子與這些表面相互作用的程度，決定于在溶液中的金屬離子的濃度，因此，可能運動進入地下水或通過植物吸收。已做的大量工作，目的是通過土壤和土壤成分來評估各種重金屬的吸附或絡合，如粘土和有機質組分。一個潛在重要的有機表面已經得到人們的關注即土壤微生物種群。土壤微生

58、物通常與粘土和土壤微環(huán)境中的有機組分聯(lián)系在一起，并預計將分享金屬動態(tài)，通常是歸因于這些組分。細菌具有很高的表面面積與體積比，正如一個嚴格的物理細胞界面，應該有一個從溶液中吸附金屬的高容量。有證據表明，細菌細胞比干重的基礎上的粘土礦物在金屬去除效果上更有效。Kurek和同事觀察到由一個副球菌sp.的死細胞吸附的Cd2+，當固體溶液的比例是細菌和粘土相同時，粘質沙雷氏菌大于蒙脫石。活細胞積累了相同數量的Cd2+，象粘土。</p>

59、<p>　　幾次調查表明，由藻類、細菌和真菌絡合的金屬離子的數量較大。通過孤立的革蘭氏陽性和革蘭氏陰性細菌細胞壁結合的金屬也被評估。觀察到革蘭陽性細菌枯草芽孢桿菌、b.地衣的細胞壁結合幾種金屬的數量比革蘭氏陰性細菌大腸桿菌的細胞被膜結合的多。</p><p>　　我們對土壤環(huán)境中微生物作用的各種重金屬的行為感興趣。這項工作的目標是，確定兩種革蘭氏陽性和兩種革蘭氏陰性菌的完整細胞的金屬結合能力，以確定

60、是否是一個均衡模型，符合Freundlich吸附等溫線，就充分說明細菌吸附金屬。研究蠟狀芽孢桿菌、枯草芽孢桿菌和綠膿桿菌作為從土壤中經常分離的常見品種的代表。大腸桿菌也被用來作為第二種革蘭氏陰性菌，因為它是一個有良好的特點的微生物，其細胞被膜已經被證明比枯草芽孢桿菌細胞壁綁定的金屬少。在本次調查中使用的四種金屬離子為Ag+、Cd2+、Cu2+和La3+。鎘和銅都是環(huán)境確定的毒離子。個別的單價和三價重金屬代表的銀和鑭，也有毒但不經常在環(huán)境

61、中發(fā)現的。</p><p><b>　　物料和方法</b></p><p>　　細菌的生長條件。在這些實驗中使用的細菌是蠟狀芽孢桿菌ATCC11778、銅綠假單胞菌ATCC14886，獲得都來自美國典型培養(yǎng)物保藏；枯草芽孢桿菌168和大腸桿菌K-12 strainAB264，都從圭爾夫大學獲得。細菌是在5倍腦心浸膏培養(yǎng)基（洗液微生物系統(tǒng)）修改的HEPES 2.4克（N

62、 - 2 - hydroxyethylpiperazine- N -2-乙磺酸）2.0 g/L的MES（2 - Nmorpholinoethanesulfonic酸）1升緩沖介質酸度中常規(guī)培養(yǎng)成的。用0.5 mol/L KOH中等酸度調整pH值為6.8。在3升的錐形瓶中兩個2毫升的指數后期階段發(fā)酵樣本被用來接種800毫升肉湯。細胞后期指數階段是生長在室溫下150轉的軌道搖床上（約23℃）。以這種方式種植的蠟狀芽孢桿菌細胞仍保持在營養(yǎng)狀況

63、。收獲的細胞，通過離心和用0.5 mol/L的硝酸調整pH 為4.0的冷的10 mmol/L的Ca（NO3）2洗滌2次。洗滌細胞被懸浮在濃度為12 mg/mL（干重）的Ca（NO3）2溶液中，并儲存在2 - 5°C 下4 h后再使用。Ca（NO3）2溶液也被用來補足所有</p><p>　　金屬吸附的研究。在這項研究中使用的四種金屬鹽類是AgNO3，Cd(NO3)2·4H2O，Cu(NO3)2

64、·2.5H2O和La(NO3)2·6H2O。金屬溶液是用0.5 mol/L的硝酸調整pH值至4.0，以避免從CuCO3 析出Cu。在pH 4.0的溶液中完成這些金屬的鑒定是通過GEOCHEM計算機程序。在pH值4.0的一個CA（NO3）2基質中，對這些金屬離子進行了預測，發(fā)現主要是自由離子的形式（在所有情況下> 97％）。</p><p>　　在這些研究中使用的塑料制品是被浸在3 mol

65、/L的硝酸中，并用雙去離子水沖洗數次，在使用前要避免金屬污染。一個批次的平衡方法被用于確定由細菌吸附的金屬。2毫升的洗滌細胞被放置在含有6毫升的冷10 mmol/L的Ca（NO3）2的10毫升聚丙烯離心管，并添加1毫升的金屬儲備溶液。試管被限制放置在一個反相振動篩上，并在5°C下平衡2 h。兩小時后，通過離心從溶液中分離出細胞，并收集上清液，用于金屬分析。均衡金屬濃度是通過電感耦合氬等離子體光譜在Thermo賈雷爾灰等離子30

66、0光譜儀被測定。在干重的基礎上，金屬量的去除是通過細胞被確定的。為了確定吸附等溫線，最終Cd2+的金屬濃度分別為1，0.1，0.01，0.001 mmol/L。初步實驗結果表明，從0.001 mmol/L處理中吸附的Cu2+會導致平衡濃度低于檢測限。隨后，Cu2+的使用最稀的濃度為0.005 mmol/L。從0.01和0.001 mmol/L的溶液中吸附的Ag+和La3+也通常導致濃度低于檢測限。銀、鑭評價的濃度為10、1、0.1、0.

67、01 mmol/L。</p><p>　　作為一個不平衡的四四格成立的吸附實驗，隨著時間的推移，重復三次。在所有四種金屬的濃度中每個區(qū)組內重復包含了四個不同的細菌金屬組合。在適當的時候，通過DAO等概述的方法和方差分析的統(tǒng)計程序程序構建吸附等溫線。</p><p>　　電子顯微鏡。通過電子顯微鏡可觀察到細菌細胞中金屬的位置。如上所述，使用1 mmol/L的金屬溶液均衡細胞，固定30分鐘，在

68、室溫下 5％戊二醛（EM級；Polysciences公司）含有金屬的濃度約等于平衡濃度。接著用戊二醛的金屬溶液洗滌細胞，穿過2%瓊脂（瓊脂實驗室），脫水通過乙醇—環(huán)氧丙烷氧化物，并嵌入在SPURR中（polysciences股份有限公司）。在賴克特Ultracut電子超薄切片機上對嵌入式細胞進行輕薄切片，并在高聚物涂層200目銅或鋁格柵上收集切片。部分金屬處理的細胞不著色；作為一個對比藥劑通過吸附金屬來提供電子散射。有些抑制的細胞被淡染

69、，用2％醋酸鈾淡染2分鐘，以提供更好的可視化效果。電子顯微鏡在100千伏的配有EDAX X射線能量分散光譜儀和Tracor Northern多通道分析儀的飛利浦EM-400下進行的。能量色散X射線分析被用來確認細胞中金屬成分。</p><p>　　親和系列的制定。為了進一步闡明細菌細胞對這些金屬的親和力，在初始濃度為1 mmol/L單一金屬或所有的四種金屬濃度為1 mmol/L溶液中放置2小時5攝氏度溫度下，細胞

70、達到均衡。如上所述，所有金屬的溶液是在PH值為4的10 mmol/L Ca（NO 3）2下被制成的。離心獲得細胞后，通過電感耦合氬等離子體光譜測定上清液中的金屬。實驗重復三次。運用SAS統(tǒng)計程序的方差程序，和最少顯著差法分離手段進行數據分析。 </p><p><b>　　研究結果</b></p><p>　　通過Freundlich吸附等溫方程線性化，更好地描述細菌

71、從溶液中吸附Cu2+和Cd2+的情況，</p><p>　　log10S = log10K + nlog10C</p><p>　　表1 由細菌吸附Cd2+和Cu2+的Freundlich等溫線</p><p>　　log K是截距，n是回歸線的斜率。常數K代表在1umol/L的平衡濃度下微摩爾每克吸附的金屬量（log C = 0）。</p><

72、;p>　　這里S是微摩爾每克吸附的金屬量，C為微摩爾每升平衡溶液的濃度，K和n是Freundlich方程常數。表1中給出的四種細菌吸附Cd2+和Cu2+的Freundlich方程的常數。常數K代表預計在1umol/L的平衡濃度下金屬微摩爾每克干細胞中移除的金屬量，n為等溫線的斜率。鎘吸附的K值的檢查結果顯示，革蘭氏陰性菌大腸桿菌在Cd吸附上是最有效的，綠膿桿菌也傾向于比革蘭氏陽性菌吸收更多的Cd2+。1umol/L平衡濃度下枯草桿

73、菌去除Cu2+最多。然而，在銅的吸附中只有1.9倍的差異，觀察之間的最高和最低的有效的細菌，分別是枯草芽孢桿菌和蠟狀芽孢桿菌。Cd2+和Cu2+的吸附等溫線代表圖，如圖1所示。協(xié)方差分析表明，等溫線的斜率分別是不同的四種細菌；在高平衡濃度下，從溶液中去除Cd2+和Cu2+最高和最低有效分別是綠膿桿菌和蠟狀芽孢桿菌。</p><p>　　圖1 通過蠟狀芽孢桿菌和綠膿桿菌吸附鎘（a）和銅（b）的Freundlich

74、等溫線。虛線代表等溫線約95％置信區(qū)間。</p><p>　　圖2 從溶液中去除銀作為初始銀濃度的函數。在濃度為10到1000 umol/L的范圍內，從所有基準點最小二乘法回歸分析所得的線是log y =-0.446 + 0.980 log x， r^2 = 0.986。</p><p>　　去除La3+的細菌之間有著顯著差異，發(fā)現在1 mmol/L的處理時，蠟狀芽孢桿菌、大腸桿菌、枯草

75、芽孢桿菌、綠膿桿菌，分別去除33、70、114和144 umol/g（圖3）。從10或100 umol/L的溶液中去除La3+的細菌之間沒有顯著差異。在1mmol/L濃度中細菌細胞與La明顯飽和，正如從10mmol/L的La3+處理中很少額外的La3+被這些細胞綁定（圖3）。</p><p>　　圖3 由細菌從一個濃度范圍內吸附的鑭。線代表標準誤差的平均值。</p><p>　　在1和0

76、.1 mmol/L的濃度（表2）的溶液中去除白銀比其他金屬更有效。在0.1 mmol/L處理中平均99％總的Ag+從溶液中被去除。鎘由細胞的綁定程度要小得多，從1 mmol/L和0.1mmol/L的處理中去除總Cd2+，分別只有12％和23％。即使在0.001 mmol/L的處理中，溶液仍保持著平均46%的添加Cd2+（數據未顯示）。</p><p>　　表2 從1和0.1 mmol/L的Ag+、Cd2+、Cu

77、2+和 La3+</p><p>　　的溶液中去除金屬綁定的數量和總金屬百分比</p><p>　　吸附是指在P=0.05時通過最顯著的差異的方法在遵循的列內，相同的字母都沒有顯著不同。括號內數字為總金屬去除的百分比。這是所有測試細菌的平均數據。</p><p>　　圖4 透射電子顯微鏡枯草桿菌細胞與1mmol/L Ag+平衡。箭頭表示與細胞相關的銀聚集體。相似細

78、胞的能量色散X射線分析證實，沉淀物組成是銀條，100納米。</p><p>　　金屬處理的細胞的電子顯微鏡照片顯示，Ag與細胞相關聯(lián)的主要是離散粒子，達到或接近細菌的細胞壁，不管他們是革蘭氏陽性或革蘭氏陰性（圖4）。能量色散X-射線分析證實了其顆粒是銀。也作了嘗試，在顆粒中使用選擇區(qū)電子衍射以確定銀的形式；然而，顆粒太小，無法產生有用的轉化。在細胞薄片上也很容易觀察到鑭。綁定的鑭被觀察到作為針狀沉淀均勻的沉積在細

79、胞壁外圍（圖5）。能量色散X-射線衍射分析證實，綁定的金屬是鑭，選擇區(qū)電子衍射分析表明，沉淀是結晶。沒有證據說明銀或鑭均勻分散在細胞質中，象征著被加強的吸收。然而，在細胞質中偶爾發(fā)現了離散的Ag顆粒（約1％的細胞），一般靠近細胞質膜，并有可能這些細胞代表無生存能力的細菌數量。</p><p>　　圖5 透射電子顯微鏡銅綠假單胞菌細胞與1 mmol/L的La3+平衡。相似細胞的能量色散X射線分析證實，沉淀物組成是

80、La。</p><p>　　無論是Cu2+或Cd2+都不能提供足夠的電子散射肯定的確定沉積的部位。這兩種金屬顯然是彌漫分布在整個細菌的細胞壁上。能量色散X射線分析表明，在細胞壁上目前主要是是銅，雖然在細胞質中也發(fā)現了少量的銅。檢測薄片發(fā)現鎘在這樣低的數量下沒有被綁定。鉀是在所有細胞中檢測到的常量元素，Cd在能量分散譜上和一個K線重疊（K =3.31千電子伏；CD =3.13千電子伏）（32）；這可能會使一個Cd的

81、頂峰被掩蓋。然而，在整個支架的細胞中鎘被檢測到一個擴大的高峰（數據未顯示）。</p><p>　　這些離子的細菌細胞的親和力在1 mmol/L濃度中下降的順序是Ag+>La3+> Cu2 +>Cd2+。當細胞與單一金屬平衡時，吸收的Cu2+和La3+本質上是相等的。然而，當細胞與所有四種金屬的混合物平衡時，La3+吸附作用總是超過Cu2+的吸附作用（見表3）。當其他陽離子存在時，每種金屬的結合減

82、少，說明一些金屬結合位點的競爭是在細胞表面上。平均而言，吸附金屬為61％Ag， 22％La，13％的Cu，和4％的Cd。</p><p>　　表3 從溶液中吸附金屬，包含一種單一的金屬或所有四種金屬</p><p>　　分離方式可以用下列公式計算：最顯著的差異（0.05）=11umol/g。這些數據是所有四</p><p>　　種細菌的平均值。每個金屬的初始濃度為

83、1mmol/L。</p><p><b>　　討 論</b></p><p>　　這項研究的目的是評估選定的革蘭氏陽性和革蘭氏陰性菌的金屬吸附能力，并確定Freundlich吸附等溫線是否可能被用于評估細菌金屬的結合。雖然吸附等溫線傳統(tǒng)上被用來形容化學計量的固體溶質相互作用，如吸附、化學吸附、離子交換，但是在一定溶液濃度范圍內它們也被用來形容通過微生物和細菌胞外

84、聚合物去除各種離子的作用（17，14，23，24）。然而，當使用完整的細菌細胞時，除了可能發(fā)生表面的吸附外必須考慮其他進程。這些交替的過程，包括通過非特異性陽離子運輸系統(tǒng)主動地吸收進入細胞質中的金屬，和沉淀在細胞表面的金屬。例如，鎘已被證明是通過一個能源依賴錳的運輸系統(tǒng)被運送到枯草桿菌的細胞之中（18）。這里使用的吸附表明，金屬是在一個或多個這些進程中被去除。</p><p>　　我們相信， Freundlich

85、等溫線描述鎘和銅的吸附是準確。對細菌之間進行了預測，鎘和銅的吸附能力存在著差異，但是，這些差異相對較小，尤其是在低濃度時。革蘭氏陰性菌，特別是大腸桿菌，在低濃度的溶液中去除更多的鎘，這符合Freundlich K常數的預測。</p><p>　　在我們工作的基礎上，對于銅的吸附，沒有概括革蘭氏陰性菌和革蘭氏陽性菌之間的差異。平衡濃度為1 mmol/L時，預計銅的吸附中只有1.9倍的差異，觀察的最高和最低的有效的細

86、菌，分別是枯草芽孢桿菌和蠟狀芽孢桿菌。在較高濃度時，對吸附銅最有效的細菌是銅綠假單胞菌。</p><p>　　對比革蘭氏陽性和革蘭氏陰性菌之間的細微差別，通過孤立的細胞壁和這些細菌群體被膜觀測金屬綁定。貝弗里奇和伊夫（3）報道，枯草桿菌和B.地衣的細胞壁綁定的Cu2+比大腸桿菌細胞膜多28至33倍。與此同時，其枯草桿菌細胞壁的制劑在干重基礎的摩爾上比在整個細胞實驗中使用的報告絡合的銅多（2990 umol/g；3

87、）。這有很好的解釋。完整的細胞明顯比提純的細胞壁或細胞膜化學性質復雜得多。大多數細菌的干重駐留在細胞質中作為無機成分的一個多元化的系列，蛋白質、核酸、脂類和碳水化合物。有毒金屬很少侵犯帶電細胞質膜，除非它為了在細胞內的解毒或迅速再次抽出而通過專門的搬運進入細胞。前者必須先被誘導，然后染色體被表示，這是不太可能發(fā)生在我們的實驗中的。因此，在我們的實驗中，保留的帶電的膜將確保細胞質中重金屬濃度可以忽略不計，能量色散X射線衍射分析證實這個事實

88、。由于大多數銅與細菌表面相關，大多數細菌的質量與細胞質相關，比較提純的細胞壁制劑，完整的細胞金屬質量比例往往偏低。這個論點假設銅的綁定基本上是被控制的，通過在細胞表面上帶負電荷的羧基和磷組互動很少或不沉淀。這個假設是通過銅（和鎘）的吸附數據適合Freun</p><p>　　除了考慮金屬質量，一些表面綁定的金屬連同作為更替和自溶的溶壁聚合物被去除，這是可能的。雖然金屬綁定實驗是在低溫和有毒金屬含量下進行的，一些代