High Mg/Ca Molar Ratios Promote Protodolomite Precipitation Induced by the Extreme Halophilic Bacterium Vibrio harveyi QPL2

Zuozhen Han; Peilin Qi; Yanyang Zhao; Na Guo; Huaxiao Yan; Maurice E Tucker; Dan Li; Jiajia Wang; Hui Zhao

doi:10.3389/fmicb.2022.821968

High Mg/Ca Molar Ratios Promote Protodolomite Precipitation Induced by the Extreme Halophilic Bacterium Vibrio harveyi QPL2

Front Microbiol. 2022 Apr 5:13:821968. doi: 10.3389/fmicb.2022.821968. eCollection 2022.

Authors

Zuozhen Han^{1

2}, Peilin Qi¹, Yanyang Zhao¹, Na Guo¹, Huaxiao Yan³, Maurice E Tucker^{4

5}, Dan Li¹, Jiajia Wang¹, Hui Zhao³

Affiliations

¹ Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Minerals, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao, China.
² Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
³ Department of Bioengineering, College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao, China.
⁴ School of Earth Sciences, University of Bristol, Bristol, United Kingdom.
⁵ Cabot Institute, University of Bristol, Bristol, United Kingdom.

Abstract

Bacterial activities have been demonstrated as critical for protodolomite precipitation in specific aqueous conditions, whereas the relationship between the various hydrochemical factors and bacterial activity has not been fully explored. In this study, biomineralization experiments were conducted using a newly isolated extreme halophilic bacterium from salina mud, Vibrio harveyi QPL2, under various Mg/Ca molar ratios (0, 3, 6, 10, and 12) and a salinity of 200‰. The mineral phases, elemental composition, morphology, and crystal lattice structure of the precipitates were analyzed by XRD, SEM, and HRTEM, respectively. The organic weight and functional groups in the biominerals were identified by TG-DSC, FTIR, and XPS analysis. The amounts of amino acids and polysaccharides in the EPS of QPL2 cultured at various Mg/Ca molar ratios were quantified by an amino acid analyzer and high-performance liquid chromatography. The results confirm that disordered stoichiometric protodolomite was successfully precipitated through the activities of bacteria in a medium with relatively high Mg/Ca molar ratios (10 and 12) but it was not identified in cultures with lower Mg/Ca molar ratios (0, 3, and 6). That bacterial activity is critical for protodolomite formation as shown by the significant bacterial relicts identified in the precipitated spherulite crystals, including pinhole structures, a mineral coating around cells, and high organic matter content within the crystals. It was also confirmed that the high Mg/Ca molar ratio affects the composition of the organic components in the bacterial EPS, leading to the precipitation of the protodolomite. Specifically, not only the total EPS amount, but also other facilitators including the acidic amino acids (Glu and Asp) and polysaccharides in the EPS, increased significantly under the high Mg/Ca molar ratios. Combined with previous studies, the present findings suggest a clear link between high Mg/Ca molar ratios and the formation of protodolomite through halophilic bacterial activity.

Keywords: EPS; Mg/Ca molar ratio; amino acids; extreme halophilic bacteria; polysaccharides; protodolomite.