球形赖氨酸芽孢杆菌(Lysinibacillus sphaericus)和嗜冷芽孢八叠球菌(Sporosarcina psychrophila)介导形成白云石晶体

Dolomite precipitation mediated by Lysinibacillus sphaericus and Sporosarcina psychrophila

【目的】白云石(Dolomite)是一种含有钙镁的碳酸盐矿物[CaMg(CO3)2],广泛存在于陆地和海洋等环境并常与油气埋藏共存。尽管白云石(或岩)的发现已经有三百多年的历史,但是对白云石的成因仍然没有定论,地质学上称之为"白云石之谜"。20世纪90年代Vasconcelos C.提出了"微生物白云石模型",为白云石成因的研究带来了新的思路。但是这一模型并不完善,白云石的形成与所介导的微生物生理状态以及环境参数之间的关系不明确。另外,所有报道的实验都是在地表压强条件下进行,无法表征自然界中白云石所处的高压环境。本研究中引入压力这一环境参数,结合菌株本身生理特性参数,综合考察多重因子对微生物介导形成白云岩的影响。【方法】利用球形赖氨酸芽孢杆菌(Lysinibacillus sphaericus)和嗜冷芽孢八叠球菌(Sporosarcina psychrophila)两株具有尿素水解活性的细菌作为生物材料,在不同的温度(15°C和30°C)压强(常压和20 MPa)氧气浓度(常压好氧条件和常压微氧条件)不同的尿素水解活性下进行生物矿化实验。通过SEM(扫描电子显微镜)和EDS(X射线能谱分析)相结合的方法观察沉淀物形貌和矿物成分构成。通过XRD(X射线衍射分析)定性测定碳酸盐矿物沉淀物的种类。【结果】球形赖氨酸芽孢杆菌和嗜冷芽孢八叠球菌在实验中所设计的所有矿化条件下都能够介导形成碳酸盐矿物沉淀。XRD和SEM检测均证实球形赖氨酸芽孢杆菌在30°C的20 MPa微氧条件下能够介导形成不规则菱面型和椭球型白云石。高压条件更有助于白云石的形成。除了白云石晶体,实验中还观察到有其他矿物(如方解石,碳氢镁石,钙镁碳酸石等)。【结论】实验证实球形赖氨酸芽孢杆菌和嗜冷芽孢八叠球菌具有矿化能力,特别是球形赖氨酸芽孢杆菌具有介导形成白云石的能力。微生物介导形成的碳酸盐矿物组分受到微生物的代谢活性以及温度、压力等生物矿化实验条件控制。这一研究结果帮助完善"微生物白云石模型",为解释白云石的深部成因提供数据支持。

[Objective] Dolomite [CaMg（CO3）2], a carbonate mineral composed of calcium and magnesium carbonate is widely distributed both in terrestrial as well as in marine environments including petroleum reservoirs. It has been more than three centuries since dolomite was discovered for the first time. However the origin of dolomite remains unclear, which was referred to as＂dolomite problem＂. In 1990＇s Vasconcelos C. from Swiss Institute of Technology proposed a model for ＂microbial dolomite formation＂, which provided a new perspective on the origin of dolomite.However, this model is not yet optimized to fully clarify the relationship between dolomite formation, bacterial physiology and environmental parameters. The available published data on the dolomite formation mediated by microorganisms were performed at ambient temperature and pressure, which is different from the natural niche of dolomization. In this study, we introduced hydrostatic pressure as an additional environmental parameter in combination with the physiological status of bacteria in order to investigate the dolomite formation under multiple conditions. [Methods]Two strains, Lysinibacillus sphaericus and Sporosarcina psychrophila, which express urea hydrolysis activity, were used as biomass to mediate dolomite precipitation under different environmental conditions like temperature（15℃ and 30℃）, pressures（ambient and 20 MPa） and oxygen concentrations（aerobic and micro-aerobic）. To determinate the morphology and component of carbonate precipitation, SEM（scanning electron microscope） combined with EDS（Energy Dispersive X-ray Spectrometry） analysis was performed. To determinate the mineralogy of carbonate precipitation, XRD（X-ray diffraction） analysis was performed. [Results] Both L. sphaericus and S.psychrophila were able to induce carbonate precipitation under all of the given experimental conditions. Both SEM and XRD results confirmed the irregular rhombohedral and spherical dolomite formation mediated by L. sphaericus at 30℃ under 20 MPa pressure and micro-aerobic condition. In addition to dolomite, other minerals（e.g. calcite, nesquehonite, huntite） were also detected to be present in precipitation. [Conclusion] This study has demonstrated that both L. sphaericus and S.psychrophila are able to mediate carbonate precipitation. Especially L. sphaericus is proven to induce dolomite formation under certain conditions. Dolomite formation is significantly influenced by urea hydrolysis activity, temperature and pressure. Our results provide evidence to explain the origin of dolomite from deep sphere and help to optimize the model of ＂microbial dolomite formation＂.