Abstract
Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO3) precipitation (MICP) in three ureolytic bacterial strains from the Sporosarcina family, including S. newyorkensis, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO3 polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO3 polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs.
Highlights
Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation
This study focuses on three different ureolytic bacterial strains, all belonging to the Sporosarcina species: Sporosarcina pasteurii (ATCC 11859), Sporosarcina aquimarina (ATCC BAA-723), and Sporosarcina newyorkensis–a newly isolated microbe from the deep sea in offshore Japan extracted by the National Institute of Advanced Industrial Science and Technology (AIST) using pressure-core nondestructive analysis tools[29]
The mineralogy, morphology, and properties of precipitates were characterised using an array of complementary techniques, namely thermogravimetric analysis coupled with mass spectroscopy (TGA-Mass spectroscopy (MS)), Raman spectroscopy (RM), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM); and the precipitation kinetics of the three microorganisms quantified through measurement of calcium ion (Ca2+) concentrations and pH (Table S4)
Summary
Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. Results strongly suggest that the presence of structural water together with specific amino acids is fundamental to the stabilisation of vaterite and that, at the same initial OD600 and treatment conditions, different strains yield distinctly different polymorphs For this reason, we compared the precipitation kinetics, and the pressure-temperature dependence of bacterial population and urease activity for the three microorganisms. Our results suggest that strain-specific CaCO3 precipitation occurs during ureolytic MICP, possibly due to differences in the urease enzyme, and its response to treatment concentrations and pressure-temperature variations, and that CaCO3 polymorphism in biotic systems is far more common than previously anticipated This may have significant implications for biomediated soil improvement systems
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