Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT, 59717, USA.
Center for Biofilm Engineering, Montana State University, Bozeman, MT, 59717, USA.
Sci Rep. 2020 Oct 16;10(1):17535. doi: 10.1038/s41598-020-73870-y.
Microbe-mineral interactions are ubiquitous and can facilitate major biogeochemical reactions that drive dynamic Earth processes such as rock formation. One example is microbially induced calcium carbonate precipitation (MICP) in which microbial activity leads to the formation of calcium carbonate precipitates. A majority of MICP studies have been conducted at the mesoscale but fundamental questions persist regarding the mechanisms of cell encapsulation and mineral polymorphism. Here, we are the first to investigate and characterize precipitates on the microscale formed by MICP starting from single ureolytic E. coli MJK2 cells in 25 µm diameter drops. Mineral precipitation was observed over time and cells surrounded by calcium carbonate precipitates were observed under hydrated conditions. Using Raman microspectroscopy, amorphous calcium carbonate (ACC) was observed first in the drops, followed by vaterite formation. ACC and vaterite remained stable for up to 4 days, possibly due to the presence of organics. The vaterite precipitates exhibited a dense interior structure with a grainy exterior when examined using electron microscopy. Autofluorescence of these precipitates was observed possibly indicating the development of a calcite phase. The developed approach provides an avenue for future investigations surrounding fundamental processes such as precipitate nucleation on bacteria, microbe-mineral interactions, and polymorph transitions.
微生物-矿物相互作用无处不在，能够促进主要的生物地球化学反应，从而推动地球动态过程，如岩石形成。其中一个例子是微生物诱导碳酸钙沉淀（MICP），其中微生物的活动导致碳酸钙沉淀的形成。大多数 MICP 研究都是在中尺度上进行的，但关于细胞包封和矿物多型性的机制仍存在一些基本问题。在这里，我们首次在 25 µm 直径的液滴中从单个产脲酶的大肠杆菌 MJK2 细胞开始，研究并描述了 MICP 在微观尺度上形成的沉淀物。随着时间的推移观察到了矿物沉淀，在水合条件下观察到了被碳酸钙沉淀物包围的细胞。使用拉曼微光谱，首先在液滴中观察到无定形碳酸钙（ACC），随后形成文石。ACC 和文石在长达 4 天的时间内保持稳定，这可能是由于有机物的存在。使用电子显微镜观察到文石沉淀物具有密集的内部结构和粒状的外部结构。这些沉淀物的自发荧光可能表明方解石相的形成。所开发的方法为未来的研究提供了途径，这些研究围绕着沉淀在细菌上的成核、微生物-矿物相互作用和多型性转变等基本过程展开。
