Bhaduri Swayamdipta, Debnath Nandini, Mitra Sushanta, Liu Yang, Kumar Aloke
Department of Mechanical Engineering, University of Alberta.
Department of Mechanical Engineering, York University.
J Vis Exp. 2016 Apr 16(110):53253. doi: 10.3791/53253.
The particular bacterium under investigation here (S. pasteurii) is unique in its ability, under the right conditions, to induce the hydrolysis of urea (ureolysis) in naturally occurring environments through secretion of an enzyme urease. This process of ureolysis, through a chain of chemical reactions, leads to the formation of calcium carbonate precipitates. This is known as Microbiologically Induced Calcite Precipitation (MICP). The proper culture protocols for MICP are detailed here. Finally, visualization experiments under different modes of microscopy were performed to understand various aspects of the precipitation process. Techniques like optical microscopy, Scanning Electron Microscopy (SEM) and X-Ray Photo-electron Spectroscopy (XPS) were employed to chemically characterize the end-product. Further, the ability of these precipitates to clog pores inside a natural porous medium was demonstrated through a qualitative experiment where sponge bars were used to mimic a pore-network with a range of length scales. A sponge bar dipped in the culture medium containing the bacterial cells hardens due to the clogging of its pores resulting from the continuous process of chemical precipitation. This hardened sponge bar exhibits superior strength when compared to a control sponge bar which becomes compressed and squeezed under the action of an applied external load, while the hardened bar is able to support the same weight with little deformation.
此处所研究的特定细菌（巴氏芽孢杆菌）具有独特的能力，即在合适的条件下，通过分泌脲酶在自然环境中诱导尿素水解（尿素分解）。通过一系列化学反应，这种尿素分解过程会导致碳酸钙沉淀的形成。这被称为微生物诱导碳酸钙沉淀（MICP）。本文详细介绍了MICP的适当培养方案。最后，进行了不同显微镜模式下的可视化实验，以了解沉淀过程的各个方面。采用光学显微镜、扫描电子显微镜（SEM）和X射线光电子能谱（XPS）等技术对最终产物进行化学表征。此外，通过定性实验证明了这些沉淀物堵塞天然多孔介质内部孔隙的能力，该实验中使用海绵条模拟具有一系列长度尺度的孔隙网络。浸入含有细菌细胞的培养基中的海绵条会因化学沉淀的持续过程导致其孔隙堵塞而变硬。与在外部施加负载作用下会被压缩和挤压的对照海绵条相比，这种硬化的海绵条表现出更高的强度，而硬化的海绵条能够支撑相同的重量且几乎没有变形。
