中文摘要：

不少微生物都具有形成球状碳酸盐矿物的能力。对形成过程的动态跟踪研究是了解球状碳酸盐矿物形成机理的关键。利用光学显微镜和电子显微镜对Citrobacter freundii作用下球状碳酸盐矿物的形成过程进行了跟踪研究。结果表明，纳米晶体在有机物质的包裹下逐渐聚集，最终生长为具有辐射状内部结构和菱形表面纹理的球状构造。在球状构造形成之前，矿物集合体经历了花形、哑铃形、花菜形、纺锤形以及类似于十字形的多种过渡形态。对最初、过渡和最终形态进行总结，有助于理解微生物作用下的球状碳酸盐矿物形成机理，为识别微生物活动在沉积环境中遗留的痕迹提供更多有用的信息。以往的研究极少涉及Citrobacter freundii诱导碳酸盐矿物的形成。研究结果将丰富微生物促进球状碳酸盐矿化的研究内容。

英文摘要：

A large number of microbes can mediate the formation of carbonate spherulite.Tailing the process of carbonate spherulite formation is the key to understand the mechanism.Using optic microscope and electron microscope,the whole process of carbonate spherulite formation under the mediation of Citrobacter freundii was traced in this study.The results showed that nanometer crystals formed firstly,and later gradually aggregated which were embedded by organics.Finally,spherulite structure formed with radiating inner structure and prismatic rhombic surface texture.During this process,several intermediate structures occurred,mainly with the morphologies of flowers,dumbbells,cauliflowers,spindles and crosses.The structural evolution offers insight into the mechanism of carbonate spherulite formation.It might be considered as the microbial signature in carbonate sediments and rocks.Because previous studies have been rarely conducted for the carbonate precipitation by Citrobacter freundii,this study will provide more information to microbial-mediated carbonate spherulite formation.