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Carbonate biomineralization induced by Bacillus megaterium
A644
Goldschmidt Conference Abstracts 2006
Carbonate biomineralization induced by Bacillus megaterium
Molecular recognition at organic acid–calcite interface
HENRY TENG1, QIAONA HU2, BIN LIAN2, JUNFENG JI1, JUN CHEN2
HENRY TENG1, YANG CHEN2, ELLI PAULI1 1
1
Department of Chemistry, The George Washington University, Washington, DC, USA ([email protected]) 2 Department of Geosciences, Nanjing University, PR China We investigated carbonate biomineralization mediated by an eubacteria, Bacillus megaterium, isolated from a loess profile in China. Upon completing bacterial cultivation, the ensuring products were centrifuged and the crystallization experiments were carried out separately in the supernatant, the concentrated bacterial sludge, as well as the un-separated culture. XRD and SEM analyses indicate that calcite (Figs. A and B) was the dominant mineral phase formed when the bacterium was present. When the supernatant alone was used, however, a significant portion of vaterite (Fig. C) also precipitated. The results further reveal that the bacterium had a strong tendency to colonize the center area of the {1014} calcite faces. The crystal morphology suggests that the bacterial colony (Fig. D) might have promoted the growth normal to individual {1014} faces of calcite when the cell concentration was high (Fig. A), but retarded it or even caused dissolution of the immediate substrate surfaces when the concentration was low (Fig. B). In addition, SEM observed the nucleation of calcite on bacterial cell walls but do not see obvious morphological changes on the nanometer- to submicron-sized nuclei. d13C measurements prove that the crystals were further enriched in the heavier carbon isotope, implying that the bacterial metabolism was not involved in the crystallization process. Based upon these findings, we propose a mechanism for the Bacillus megaterium mediated calcite mineralization and conclude that the whole process involves epi- and inter-cellular growth in the local microenvironments whose conditions may be controlled by cell sequestration and proton pumping during bacterial respiration.
Department of Chemistry, The George Washington University, Washington, DC, USA ([email protected]) 2 Department of Geosciences, Nanjing University, PR China Interactions of aqueous organic acid with calcite crystal face find their occurrences in many natural processes such as biomineralization and metal ion sequestration. They may also be one of the critical gateways in understanding the origin of homochirality in terrestrial biomass because of the possibility of chiral adsorption of amino acids on mineral surfaces. It is generally accepted that, due to the similarity between carbonate anion (CO3 2 and carboxyl group (–COO1), the interaction is fulfilled by carboxylic acid adsorbing onto the crystal faces through electrostatic attractions of –COO1 and terminal –Ca+ surface site. This indicates that, given the ordered atomic arrangement in crystal lattice, the interaction has to be crystallographic direction specific. Previous studies of calcite–aspartate (Asp) interactions documented such direction-specific nature, and also raised questions regarding the involvement of specific functional groups and the geometry of the surface binding. Issues needing to be addressed include (1) the roles of amino acids’ side-chain functional group and the a-amine group; (2) the effect of side chain length; and (3) the coordination of multifunctional groups in surface binding. In this study, we investigated the binding direction and geometry of organic acid, including biological amino acid, on calcite surface by examining the possible molecular recognition between aqueous ion and crystal face. Experiments were conducted using a ‘molecular probing’ approach where the structure and composition of the organic acid used were varied systematically relative to Asp. The results show that when the chirality of the organic acids was maintained, such as in the case of alanine, glutamic acid, and serine, the reactions took place only on one side of the c-glide plane on the {10 14} faces and the side preference depended upon the chirality of the organic acids. When the chirality was removed, such as in the case of succinic acid, the c-glide plane lost its control on the reaction. Instead, two new directions, ½42 1 and [010], along with the inherent ½ 441 and ½48 1, developed and the new directions were different from the ones stabilized by Asp, [45 1] and [41 1]. Additionally, the Asp-preferred directions did not appear when the side chain length or functional group was changed, such as in the case of alanine, glutamic acid, and serine. These results will be discussed in terms of electrostatic matching, geometric correspondence, and stereochemical conformity between the organic acids and various steps on the {10 14} faces. On the basis of these observations, we propose a general binding geometry for multi-functional organic acids to interact with calcite surfaces. doi:10.1016/j.gca.2006.06.1200
doi:10.1016/j.gca.2006.06.1199
Goldschmidt Conference Abstracts 2006
Carbonate biomineralization induced by Bacillus megaterium
Molecular recognition at organic acid–calcite interface
HENRY TENG1, QIAONA HU2, BIN LIAN2, JUNFENG JI1, JUN CHEN2
HENRY TENG1, YANG CHEN2, ELLI PAULI1 1
1
Department of Chemistry, The George Washington University, Washington, DC, USA ([email protected]) 2 Department of Geosciences, Nanjing University, PR China We investigated carbonate biomineralization mediated by an eubacteria, Bacillus megaterium, isolated from a loess profile in China. Upon completing bacterial cultivation, the ensuring products were centrifuged and the crystallization experiments were carried out separately in the supernatant, the concentrated bacterial sludge, as well as the un-separated culture. XRD and SEM analyses indicate that calcite (Figs. A and B) was the dominant mineral phase formed when the bacterium was present. When the supernatant alone was used, however, a significant portion of vaterite (Fig. C) also precipitated. The results further reveal that the bacterium had a strong tendency to colonize the center area of the {1014} calcite faces. The crystal morphology suggests that the bacterial colony (Fig. D) might have promoted the growth normal to individual {1014} faces of calcite when the cell concentration was high (Fig. A), but retarded it or even caused dissolution of the immediate substrate surfaces when the concentration was low (Fig. B). In addition, SEM observed the nucleation of calcite on bacterial cell walls but do not see obvious morphological changes on the nanometer- to submicron-sized nuclei. d13C measurements prove that the crystals were further enriched in the heavier carbon isotope, implying that the bacterial metabolism was not involved in the crystallization process. Based upon these findings, we propose a mechanism for the Bacillus megaterium mediated calcite mineralization and conclude that the whole process involves epi- and inter-cellular growth in the local microenvironments whose conditions may be controlled by cell sequestration and proton pumping during bacterial respiration.
Department of Chemistry, The George Washington University, Washington, DC, USA ([email protected]) 2 Department of Geosciences, Nanjing University, PR China Interactions of aqueous organic acid with calcite crystal face find their occurrences in many natural processes such as biomineralization and metal ion sequestration. They may also be one of the critical gateways in understanding the origin of homochirality in terrestrial biomass because of the possibility of chiral adsorption of amino acids on mineral surfaces. It is generally accepted that, due to the similarity between carbonate anion (CO3 2 and carboxyl group (–COO1), the interaction is fulfilled by carboxylic acid adsorbing onto the crystal faces through electrostatic attractions of –COO1 and terminal –Ca+ surface site. This indicates that, given the ordered atomic arrangement in crystal lattice, the interaction has to be crystallographic direction specific. Previous studies of calcite–aspartate (Asp) interactions documented such direction-specific nature, and also raised questions regarding the involvement of specific functional groups and the geometry of the surface binding. Issues needing to be addressed include (1) the roles of amino acids’ side-chain functional group and the a-amine group; (2) the effect of side chain length; and (3) the coordination of multifunctional groups in surface binding. In this study, we investigated the binding direction and geometry of organic acid, including biological amino acid, on calcite surface by examining the possible molecular recognition between aqueous ion and crystal face. Experiments were conducted using a ‘molecular probing’ approach where the structure and composition of the organic acid used were varied systematically relative to Asp. The results show that when the chirality of the organic acids was maintained, such as in the case of alanine, glutamic acid, and serine, the reactions took place only on one side of the c-glide plane on the {10 14} faces and the side preference depended upon the chirality of the organic acids. When the chirality was removed, such as in the case of succinic acid, the c-glide plane lost its control on the reaction. Instead, two new directions, ½42 1 and [010], along with the inherent ½ 441 and ½48 1, developed and the new directions were different from the ones stabilized by Asp, [45 1] and [41 1]. Additionally, the Asp-preferred directions did not appear when the side chain length or functional group was changed, such as in the case of alanine, glutamic acid, and serine. These results will be discussed in terms of electrostatic matching, geometric correspondence, and stereochemical conformity between the organic acids and various steps on the {10 14} faces. On the basis of these observations, we propose a general binding geometry for multi-functional organic acids to interact with calcite surfaces. doi:10.1016/j.gca.2006.06.1200
doi:10.1016/j.gca.2006.06.1199