Biomineralization of Carbonate Minerals Induced by Halophilic <em>Chromohalobacter israelensis</em> in High Salt Concentration: Implications for Natural Environments

Abstract

High salt environment was widespread in modern and geological record, and sedimentation induced by microbes in these systems was an important part of sedimentary minerals and rocks. The mechanism of microbiologically induced carbonate precipitation has not been solved thoroughly although numerous scholars and experts have made specifically research of the problems with respect to minerals induced by bacteria. The study of carbonate minerals induced by Halophilic bacteria has aroused wide concern. The present study was aim to investigate the characterization and process of biomineralization in the high salt system, a Halophilic bacterium, Chromohalobacter israelensis LD532 strain (Genbank: KX766026), which isolated from Yinjiashan Saltern of China, was selected as an object to induce carbonate minerals. Carbonate minerals induced by LD532 were investigated in several comparative experimental sets with Mg resources of magnesium sulfate and magnesium chloride. Magnesium calcite and aragonite were induced by LD532 bacteria while these minerals were not in the control group. The mineral phases, micromorphologies, and crystal structures were analyzed using X-ray powder diffraction, scanning electron microscope, and energy dispersive X-ray detector. Carbonic anhydrase and urease secreted by strain LD532 through metabolism promoted the pH values of the liquid medium and the process of carbonate precipitation. Further study proved that the nucleation sites of partial carbonate nucleus were located on the extracellular polymeric substance and the membrane of intracellular vesicles of LD532 bacteria by high resolution transmission electron microscopy, energy dispersive X-ray detector and ultrathin slices analysis, which provided favorable conditions for the growth of carbonate mineral crystals. The morphology and composition of minerals formed in MgSO4 and MgCl2 solution have significant differences, indicating that different sources of Mg 2+ could also affect the physiological and biochemical activities of microorganisms and then affect the mineral deposition. The accomplished study is of certain interest for interpretation of the carbonates biomineraliazation in natural salt environment, and has a certain reference value in understand of the sedimentary carbonates in ancient marine environment like evaporated tidal flat.