Abstract
Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30–50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process.
Highlights
Biomineralization as described by Lowenstam [1] is the ability of living organisms to form minerals as well as materials composed of an organic and inorganic phase [2,3]
biologically controlled mineralization (BCM) is based on a site-specific matrix that enables the formation of a compartmentalized environment with its own chemical composition
We report that C. hydrogenoformans a carboxydotrophic hydrogenogenic hyperthermophilic bacterium [12] converts an amorphous calcium phosphate phase into a fully crystalline whitlockite mineral and spherulitic clusters that we interpret to be hydroxyapatite-like nanocrystals
Summary
Biomineralization as described by Lowenstam [1] is the ability of living organisms to form minerals as well as materials composed of an organic and inorganic phase [2,3]. Biomineralization processes fall in two categories: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM) [1]. In BIM, biomineralization occurs outside the cell and none of the cell components are serving as a template for nucleation and growth of the precipitate. In this case, cellular activity results in changes in the microenvironment and anionic and cationic precipitation [3]. In BCM, known as inorganic matrix-mediated mineralization [1], the cell controls all of the above described stages of mineralization from nucleation to crystal-formation, leading to a highly specie-specific product [8]. Nucleation is made possible by sequestering specific ions leading to supersaturation and precipitation in the matrix [9]
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