A Bacterial Biofilm Polysaccharide Affects the Morphology and Structure of Calcium Oxalate Crystals

Biomineralization describes the process of mineral precipitation from soluble precursors by living organisms. It is sometimes associated with single bacterial cells, for example, the formation of magnetosomes by magnetotactic bacteria, as well as with groups of bacterial cells that form biofilms and precipitate calcium carbonate (CaCO₃). Recently, there has been growing evidence connecting isolated bacteria and bacterial biofilms with calcium oxalate (CaOx) formation in kidney stones. Therefore, in this study, we examined the effect of a principal exopolysaccharide bacterial biofilm component on the crystallization of CaOx. We observed that the exopolysaccharide, identified as levan, induced the formation of both octahedral CaOx dihydrate (COD, Weddellite) and pancake-like CaOx monohydrate crystals (COM, Whewellite) in a concentration-dependent manner. A combined analysis of the CaOx crystals that formed in the presence of levan, using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, indicated that levan affects both the nucleation and the growth of CaOx and that its interaction with CaOx is stereospecific. Given the emerging relation between bacterial biofilms and kidney stones, which are prevalent within approximately 12% of the worldwide population, it is important to decipher the effect of biofilm extracellular polymers on the formation of CaOx crystals as it may assist in the development of future treatments to interfere with kidney stone formation.