细菌作用下哑铃形碳酸盐矿物形成机制的实验研究

The mineralization mechanism of carbonate minerals by microorganism have very important implication for understanding the mechanism of mineral trapping of CO2, the origin of ancient rocks and the fixation route of soil inorganic carbon. However, biomineralization mechanism, especially, the problem about nucleation template of carbonate mineral induced by microbe is unclear to date. This proposal will simulate precipitation process of carbonate calcium in culture medium with bacteria (Bacillus cereus, Lysinibacillus sp. and Microbacterium sp.), their excreted extracellular polysaccharide and carbonate anhydrase, as well as, in chemical systems with inorganic ion and organic molecular (low molecular weight organic acids and amino acids), respectively. Present proposal is characterized by a subject cross among genetic mineralogy, microbiology and isotope geochemistry. It primarily will research on the temporal change of the morphology by using scanning electron microscopy (SEM), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). This proposal also will investigate the transformation rule of mineral species by using X-ray diffraction (XRD), micro X-ray diffraction (MXRD), selected-area electron diffraction (SAED) and Fourier transform infra-red spectrometer (FTIR), and will explore possible difference of C and O isotopic components between biogenic and abiogenic minerals using isotope ratios mass spectrometry (IRMS). The proposal would clarify the nucleation template and make clear the formation mechanism of dumbbell-shaped particles via experimental design of gradual supplements toward in the key stages of time. The research results would be helpful for exposing the actual role of microbe in the mineralization process of carbonate mineral, and further to provide the scientific evidences for clarifying the mineralization mechanism of carbonate mineral induced by microorganism.

微生物作用下碳酸盐矿物的形成机理对于理解CO2的矿物捕获机制、古老岩石的成因以及土壤无机碳的固定途径等科学问题均具有十分重要的意义。目前，微生物参与下碳酸盐的矿化机理、尤其是成核模板问题还不很清楚。本项目拟以成因矿物学、微生物学和同位素地球化学相交叉为特色，针对含有不同形状的细菌（蜡状芽孢杆菌、赖氨酸芽孢杆菌和微杆菌）、细菌胞外多糖和碳酸酐酶、无机阳离子以及有机分子的碳酸钙体系分别进行系统的实验研究。重点利用SEM、AFM和HRTEM等技术研究沉淀物形态的动态变化，使用XRD、MXRD、FTIR和SAED等技术明确矿物相的转变规律，运用IRMS法对矿物的碳氧同位素组成开展探索性的研究工作。本项目拟采用在关键时间段内逐渐加密的实验设计，以哑铃形矿物的形成机制为突破口，探究成核模板问题。研究结果将有助于揭示细菌在碳酸盐矿化过程中的确切作用，并为阐明微生物作用下碳酸盐矿化的机理提供科学依据。

微生物作用下碳酸盐矿物的形成机理对于理解CO2的矿物捕获机制、古老岩石的成因以及土壤无机碳的固定途径等科学问题均具有十分重要的意义。目前，微生物参与下碳酸盐的矿化机理还不很清楚。本项目利用多种细菌（蜡样芽孢杆菌、Curvibacter sp.、赖氨酸芽孢杆菌和微杆菌等）及其分泌的EPS和CA进行了碳酸盐矿化实验，研究了细菌密度、pH值、钙离子和HCO3-浓度、胞外多糖含量、CA活性和沉淀物重量等参数的动态变化。我们重点利用FIB、SEM和HRTEM等技术研究矿物形态的动态变化，使用XRD、FTIR和SAED等技术分析矿物相及其变化，运用IRMS和MC-ICP-MS技术分别对矿物的碳氧和镁同位素组成开展了探索性的研究工作。本项目的研究结果表明，细菌种类、密度、EPS和CA对碳酸盐矿化均有一定的贡献。SI对碳酸盐矿物种类起着决定性的作用。Mg2+对哑铃形矿物的形成起着关键性的作用。哑铃形矿物是由杆状矿物（钙化细菌）转化而来，它经过其他过渡形态最后发展为球状。钙化细菌从内到外依次为ACC、球霰石、方解石和细菌细胞。细菌成因碳酸盐矿物具有比化学成因更负的δ13C（平均值分别为-17.486‰和-4.302‰）和偏正的δ26Mg（分别为-1.850‰和-2.327‰）。镁同位素在碳酸盐矿物与溶液之间发生了显著的分馏作用（Δ26Mg固-液=-1.095‰）。细菌诱导形成的碳酸钙矿物的δ18O值变化范围较大（-11‰~-7‰）。通过本项目的研究，我们基本上弄清了哑铃形矿物的调控机制，解释了细菌在碳酸盐矿化过程中的确切作用。这些研究结果有可能为进一步阐明微生物作用下碳酸盐矿化的机理提供科学依据。