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Open AccessFeature PaperArticle

Biomineralization of Monohydrocalcite Induced by the Halophile Halomonas Smyrnensis WMS-3

1
College of Chemical and Environmental Engineering, College of Earth Science and Engineering, Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Minerals, Shandong University of Science and Technology, Qingdao 266590, China
2
Laboratory for Marine Mineral Resources, Center for Isotope Geochemistry and Geochronology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
3
School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
4
Cabot Institute, University of Bristol, Cantock’s Close, Bristol BS8 1UJ, UK
*
Authors to whom correspondence should be addressed.
Hui Zhao and Juntong Pan contributed equally and as co-first authors.
Minerals 2019, 9(10), 632; https://doi.org/10.3390/min9100632
Received: 1 September 2019 / Revised: 11 October 2019 / Accepted: 12 October 2019 / Published: 15 October 2019
(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)
The halophilic bacterium Halomonas smyrnensis from a modern salt lake used in experiments to induce biomineralization has resulted in the precipitation of monohydrocalcite and other carbonate minerals. In this study, a Halomonas smyrnensis WMS-3 (GenBank:MH425323) strain was identified based on 16S rDNA homology comparison, and then cultured in mediums with 3% NaCl concentration to induce monohydrocalcite at different Mg/Ca molar ratios of 0, 2, 5, 7, and 9. The growth curve of WMS-3 bacteria, pH values, NH4+ concentration, HCO3 and CO32− concentration, carbonic anhydrase (CA) activity, and the changes in Ca2+ and Mg2+ ion concentration were determined to further explore the extracellular biomineralization mechanism. Moreover, the nucleation mechanism of monohydrocalcite on extracellular polymeric substances (EPS) was analyzed through studying ultrathin slices of the WMS-3 strain by High resolution transmission electron microscopy (HRTEM), Selected area election diffraction (SAED), Scanning transmission electron microscopy (STEM), and elemental mapping, besides this, amino acids in the EPS were also analyzed. The results show that pH increased to about 9.0 under the influence of ammonia and CA activity. The precipitation ratio (%, the ratio of the mass/volume concentration) of the Ca2+ ion was 64.32%, 62.20%, 60.22%, 59.57%, and 54.42% at Mg/Ca molar ratios of 0, 2, 5, 7, and 9, respectively, on the 21st day of the experiments, and 6.69%, 7.10%, 7.74%, 8.09% for the Mg2+ ion concentration at Mg/Ca molar ratios 2, 5, 7, and 9, respectively. The obtained minerals were calcite, Mg-rich calcite, aragonite, and hydromagnesite, in addition to the monohydrocalcite, as identified by X-ray diffraction (XRD) analyses. Monohydrocalcite had higher crystallinity when the Mg/Ca ratio increased from 7 to 9; thus, the stability of monohydrocalcite increased, also proven by the thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The C=O and C–O–C organic functional groups present in/on the minerals analyzed by Fourier transform infrared spectroscopy (FTIR), the various morphologies and the existence of P and S determined by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), the relatively more negative stable carbon isotope values (−16.91‰ to −17.91‰) analyzed by a carbon isotope laser spectrometer, plus the typical surface chemistry by XPS, all support the biogenesis of these mineral precipitates. Moreover, Ca2+ ions were able to enter the bacterial cell to induce intracellular biomineralization. This study is useful to understand the mechanism of biomineralization further and may provide theoretical reference concerning the formation of monohydrocalcite in nature. View Full-Text
Keywords: Halomonas smyrnensis; biomineralization; monohydrocalcite; nucleation site; Mg/Ca ratios Halomonas smyrnensis; biomineralization; monohydrocalcite; nucleation site; Mg/Ca ratios
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MDPI and ACS Style

Pan, J.; Zhao, H.; Tucker, M.E.; Zhou, J.; Jiang, M.; Wang, Y.; Zhao, Y.; Sun, B.; Han, Z.; Yan, H. Biomineralization of Monohydrocalcite Induced by the Halophile Halomonas Smyrnensis WMS-3. Minerals 2019, 9, 632.

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