Pseudo-Biomineralization: Complex Mineral Structures Shaped by Microbes.

Biomineralization is an active, biologically governed process of mineral formation, established early on in the history of life. The appearance of biomineralizing organisms heavily influenced the course of evolution, leading to the development of the large diversity of the extant taxa. Yet, we are still only beginning to grasp the intricate, genetically regulated mechanisms involved. Since prokaryotic organisms were the first to emerge from the primordial environments, we investigated bacteria-mineral interactions using titration and gas diffusion systems adapted to emulate conditions, which may have facilitated the development of biomineralization initially. By screening the minerals and bacteria from titration experiments with scanning electron microscopy, we discovered a broad spectrum of behavioral strategies employed by bacteria confronted with calcification, which fell into three main categories: (1) evasion of mineralization by the formation of the biofilm, (2) random embedding into the mineral, and (3) control over the mineral shape during its formation. The latter phenomenon we termed pseudo-biomineralization. Our experiments indicate that pseudo-biomineralization is an active process obligatorily reliant on the external calcifying conditions and allowing considerable degree of control over mineral shape, thus producing structures reminiscent of true biominerals. Here, we describe this notion for the first time, thus providing vital insight into the genesis of a transitional stage to calcium carbonate-based biomineralization systems.