Contribution of selective bacterial extracellular polymeric substances to the polymorphism and morphologies of formed Ca/Mg carbonates

Abstract

Recently, evidence is accumulating on the role of bacterial extracellular polymeric substances (EPS) to the crystal growth and morphological forms of carbonates. In order to explore the function of EPS on crystal growth, EPS from Curvibacter sp. HJ-1 and Arthrobacter sp. MF-2 (HJEPS and MFEPS) were used in this study to induce carbonate precipitation at different Mg/Ca molar ratios. The obtained results showed that carbohydrates and proteins in EPS were the main functional biomacromolecules to the crystal growth of carbonate, and EPS reduced the δ13C values of minerals (approximately −16.307 and −21.898 for carbonates induced by HJEPS and MFEPS vs. −15.207 for abiotic carbonates). The presence of HJEPS was beneficial for the precipitation of aragonite, while MFEPS induced the formation of vaterite and monohydrocalcite, as well as markedly enhanced the MgCO3 content of calcite (approximately 28.20% for carbonates induced by MFEPS vs. 10.26% for abiotic carbonates). Proteins in MFEPS significantly affected the crystal structure and induced the formation of different morphologies. In contrast, carbohydrates in HJEPS induced crystal aggregation into spherical structures. These findings suggest that the physicochemical property of EPS influences the polymorph selection and the resulting morphology of Ca/Mg carbonates.