Biomineralization process is essential for exploring the interactions between geological processes and biological activity, as well as for studying the co-evolution of life and the planet through fossil records. Traditionally, extracellular microbial-induced mineralization has been considered highly sensitive to environmental conditions, making it difficult to distinguish its products from abiogenic minerals. This has limited its broader application in geological studies and biomimetic mineralization.
In this study, we continuously monitored changes in Fe concentration and mineralization products during the mineralization process mediated by the dissimilatory iron-reducing bacterium Shewanella oneidensis MR-4. We found that during the first 14 days of cultivation, the Fe(II) concentration in the supernatant remained low, and magnetite was the sole mineralization product. However, around day 20, the Fe(II) concentration peaked, and S. oneidensis MR-4 began to induce the formation of siderite and vivianite. These observations demonstrate that the Fe(II) concentration in the supernatant plays a key role in controlling mineral formation induced by dissimilatory iron-reducing bacteria. By integrating electron microscopy and STXM analyses, we propose a model for the biomineralization process of magnetite, siderite, and vivianite by S. oneidensis MR-4. Initially, the low Fe(II) produced by the bacteria rapidly reacts with ferrihydrite to form magnetite. As the bacterial cells grow and Fe(II) accumulates, it reacts with CO₃²⁻ or PO₄³⁻ in the solution, using ferrihydrite and organic molecules as nucleation sites to form siderite or vivianite. The subsequent growth of siderite particles is accompanied by morphological transformations, evolving from spindle to rod, peanut, dumbbell, and ultimately spherical forms, while vivianite primarily develops into fibrous or leaf-shaped structures.
In summary, this study not only reveals that the biomineralization of siderite and vivianite by dissimilatory iron-reducing bacteria proceeds via a "building-block" mechanism but also shows that these minerals, acting as "graves" for organic matter, contribute to the preservation of organic materials. Moreover, their distinct morphologies and the presence of internal organic molecules may serve as both morphological and geochemical signatures for identifying biogenic siderite and vivianite in the geological record. These findings also provide valuable insights for employing bacterial biomineralization in nanogeoscience applications, including environmental remediation and biomimetic mineral synthesis.

vivianite,siderite,dissimilatory iron-reducing bacteria,STXM,HR-TEM