Bacterial biomineralization is a widespread process that affects cycling of metals in the environment. Functionalized bacterial cell surfaces and exopolymers are thought to initiate mineral formation, however, direct evidences are hampered by technical challenges. Here, we present a breakthrough in the use of liquid-cell scanning transmission electron microscopy to observe mineral growth on bacteria and the exopolymers they secrete. Two Escherichia coli mutants producing distinct exopolymers are investigated. We use the incident electron beam to provoke and observe the precipitation of Mn-bearing minerals. Differences in the morphology and distribution of Mn precipitates on the two strains reflect differences in nucleation site density and accessibility. Direct observation under liquid conditions highlights the critical role of bacterial cell surface charges and exopolymer types in metal mineralization. This has strong environmental implications because biofilms structured by exopolymers are widespread in nature and constitute the main form of microbial life on Earth.

细菌生物矿化是影响环境中金属循环的广泛过程。功能化的细菌细胞表面和外聚合物被认为可以引发矿物质的形成，然而，直接证据受到技术挑战的阻碍。在这里，我们提出了使用液体细胞扫描透射电子显微镜观察细菌上矿物质生长及其分泌的外聚合物的突破。研究了两种产生不同外聚物的大肠杆菌突变体。我们使用入射电子束激发并观察含锰矿物的沉淀。两种菌株上锰析出物形态和分布的差异反映了成核位点密度和可达性的差异。液体条件下的直接观察凸显了细菌细胞表面电荷和外聚合物类型在金属矿化中的关键作用。这具有很强的环境影响，因为由外聚合物构成的生物膜在自然界中广泛存在，并且构成了地球上微生物生命的主要形式。