Biopolymers from a Bacterial Extracellular Matrix Affect the Morphology and Structure of Calcium Carbonate Crystals

Abstract

Biomineralization is a mineral precipitation process occurring in the presence of organic molecules and used by various organisms to serve a structural and/or a functional role. Many biomineralization processes occur in the presence of extracellular matrices that are composed of proteins and polysaccharides. Recently, there is growing evidence that bacterial biofilms induce CaCO3 mineralization and that this process may be related with their extracellular matrix (ECM). In this study we explore, in vitro, the effect of two bacterial ECM proteins, TasA and TapA, and an exopolysaccharide, EPS, on calcium carbonate crystallization. We have found that all the three biopolymers induce the formation of complex CaCO3 structures. The crystals formed in the presence of the EPS are very diverse in morphology and they are either calcite or vaterite in structure. However, more uniformly sized calcite crystals are formed in the presence of the proteins; these crystals are composed of single crystalline domains that assemble together into spherulites (in the presence of TapA) or dumbbell-like shapes (in the presence of TasA). Our results suggest the EPS affects the nucleation of calcium carbonate when it induces the formation of vaterite crystals and that unlike EPS, the proteins stabilize preformed calcite nuclei and induce their aggregation into complex calcite structures. Biomineralization processes induced by bacterial ECM macromolecules make biofilms more robust and difficult to remove when they form, for example, on pipes and filters in water desalination systems or on ship hulls. Understanding the formation conditions and mechanism of formation of calcium carbonate in the presence of bacterial biopolymers may lead to the design of suitable mineralization inhibitors.

Bacillus subtilis biofilm formation and social interactions

“…The structure and morphology of calcium carbonate crystals are affected by TasA, TapA and EPS in vitro, suggesting that these molecules interact with calcium ions in the biofilm 56 .…”

Multiscale X-ray study of Bacillus subtilis biofilms reveals interlinked structural hierarchy and elemental heterogeneity

“…Polysaccharide was purified from WT Bacillus Subtilis pellicles, as previously described (12,32). WT liquid culture was grown overnight in LB medium and transferred to SYN medium at a 1:100 dilution.…”

“…Bacterial biofilms are composed of vegetative cells that are embedded in a network of secreted polysaccharides, proteins and nucleic acids, termed the extracellular matrix (ECM) 3 . The ECM network provides biofilms with diverse essential properties 4 , endowing mechanical stability 5,6 , regulating spreading 7 and osmotic pressure 8 , water and mineral uptake 9 , providing a hydrophobic shield 10,11 , affecting the precipitation of minerals such as calcium carbonate 12,13 and increasing the resistance of the biofilm cells to antibiotic activity 4,14 . Under physiological stress conditions, cells in biofilms from the Firmicute phylum, such as Bacilli and Clostridia, form dormant spores, where the genome is stored in a partially dehydrated core, surrounded by a protective coat made of organized proteins and glycoproteins [15][16][17][18] .…”

Amylopectin Regulated Mineralization of Calcium Carbonate and Its Application in Removing of Pb(II)

“…[16] Organic additives are often considered as a template for mineralization, [7,17] functional groups on the additives can react with calcium ions to provide nucleation sites of CaCO 3 and induce it to form crystals of various morphology, sizes, orientations, functions, etc. [18][19][20][21][22][23][24][25] As far as we know, the study of organic additives is mainly focus on soluble matrix, and few researches are reported on insoluble matrix. As a major component of the organic matter in the sticky rice, amylopectin is insoluble in water and most organic solvents, which plays an important role in repair and maintenance of cultural relics.…”