细菌碳酸酐酶促进形成的碳酸盐矿物

Carbonic anhydrase excreted by bacteria induces the formation of carbonate minerals

微生物促进碳酸盐矿化机理的研究对于全球碳循环和土壤的形成与演化等科学问题具有重要的意义。为了探究细菌胞外碳酸酐酶(CA)在碳酸盐矿化过程中所起的作用,本文采用硫酸铵析出蛋白质和Tris-H2SO4缓冲液溶解蛋白质的方法提取MF-2菌株分泌的胞外CA,将其添加于一水乙酸钙—胰蛋白胨(不含碳酸根)体系中并进行了120h的化学实验。同时设置一组不含CA的对照实验。实验结束后用离心法将固相和液相分离。利用X-射线衍射仪(XRD)和扫描电子显微镜(SEM/EDS)对沉淀物的矿物成分、元素组成和形态进行了研究,利用电感耦合等离子体发射光谱仪(ICP-OES)测定了溶液中的Ca2+浓度。实验结果表明:(1)在节杆菌属MF-2菌株胞外CA作用下形成了肉眼可见的沉淀物,其重量随着反应时间的延长而逐渐增大,而溶液中钙离子浓度随着反应时间的延长而逐渐降低。用双氧水(30%)处理的结果显示,碳酸盐矿物是沉淀物的主要组分。对照实验形成的沉淀物明显少于CA实验,而且其主要由有机物质组成。这充分地说明,MF-2菌株胞外CA可以显著地促进碳酸盐矿物沉淀。(2)在有胞外CA参与的实验早期(第48h之前),未形成任何结晶态物质;在实验的中后期,形成的矿物以方解石为主,含少量或不含球霰石。这明显不同于MF-2菌株的培养实验。在后一种情况下仅形成球霰石一种矿物。(3)胞外CA作用下形成的矿物形态包括菱面体形、球形和半球形,其中菱面体形矿物占主导地位。这也有别于MF-2菌株的培养实验(以球状和碗状为主)。对多张SEM照片进行的统计结果显示,菱面体形矿物所占比例有随着反应时间的延长而逐渐降低的趋势(即球形和半球形所占比例逐渐升高),从第48h的接近100%降低至第120h的84%。(4)MF-2菌株胞外CA促进碳酸钙沉淀的主要机制是其加速CO2的水化反应,参与反应的CO2可能主要源于空气。

Study on the mechanism of carbonate mineralization in the presence of microorganisms is of great significance for the global carbon cycle,soil formation and evolution and other related issues.In order to clarify the role of extracellular carbonic anhydrase（CA）excreted by bacteria in the process of carbonate mineralization,a series of chemical experiments were carried out in the CA-calcium acetate-tryptone（without carbonate）system for 120 hours.The extracellular CA from MF-2 strains was extracted through precipitation of protein by ammonium sulfate and dissolution of protein by Tris-H_2SO_4 buffer solution.Synchronously,a series of control experiments without CA were performed.After the experiments,the solid and the liquid phases were separated using the centrifugation method.The mineral species,its chemical composition and morphology were characterized by X-ray diffractometer（XRD）and scanning electron microscope accompanied by energy-dispersive spectrometry（SEM/EDS）.The concentration of calcium ion in the solution was determined by the inductively coupled plasma optical emission spectrometer（ICP-OES）.The results show that（1）the precipitate with visible amount formed in the system with extracellular CA.With the prolongation of the reaction time,the precipitate weight increased gradually,while the Ca2＋concentration in the solution decreased.The treatment results with 30% hydrogen peroxide show that carbonate mineral was the dominant component in the precipitate.The precipitate formed in the control experiments was significantly less than that in the CA experiments,which was mainly composed of organic substances.This adequately demonstrates that the extracellular CA excreted by MF-2strain could significantly promote precipitation of carbonate minerals.（2）No crystalline formed in the initial stage of experiments（before 48 th h）with CA,and calcite was dominant mineral in the precipitate formed in the middle and late stages.This was obviously different from the incubation experiments with MF-2strain.Only vaterite formed in the latter case.（3）The mineral morphologies formed by the action of extracellular CA were rhombohedral,spherical and hemi-spherical,in which then rhombohedral mineral dominated.This was also different from the incubation experiments with MF-2strain（spherical and bowl-shaped in the latter case）.The statistical results based on several SEM photographs show that the proportion of rhombohedral-shaped minerals decreased gradually with time,from nearly 100% at 48 th h to 84%at 120 th h,i.e.spherical and hemi-spherical minerals gradually increased.（4）CA accelerated hydration reaction of carbon dioxide and promoted formation of carbonate minerals.The CO2 participated in the reaction might largely come from air.