Geobacillus thermoglucosidasius Endospores Function as Nuclei for the Formation of Single Calcite Crystals

Abstract

Geobacillus thermoglucosidasius colonies were placed on an agar hydrogel containing acetate, calcium ions, and magnesium ions, resulting in the formation of single calcite crystals (calcites) within and peripheral to the plating area or parent colony. Microscopic observation of purified calcites placed on the surface of soybean casein digest (SCD) nutrient medium revealed interior crevices from which bacterial colonies originated. Calcites formed on the gel contained [ Biomineralization is defined as the synthesis of inorganic crystalline or amorphous mineral-like materials by living organisms. Bacteria are capable of forming inorganic crystals either intracellularly (1) or extracellularly (2). Magnetic bacteria migrate along the lines of the earth's magnetic field and synthesize intracellular particles of magnetite that are aligned in a chain-like fashion and enveloped by a membrane (3, 4). The use of bacterial magnetic particles in biomedical applications is increasing because they are easy to handle and to separate from biological samples. In particular, the lipid bilayer surrounding magnetic particles is reportedly amenable to insertion of recombinant transmembrane proteins (5, 6). Calcite (calcium carbonate) precipitation is a well-known example of extracellular bacterial biomineralization. The precipitation of calcium carbonates by Halobacillus trueperi (spore-forming, moderately halophilic bacterium) isolated from hypersaline sediments of the Great Salt Lake in Utah has been investigated (7). Scanning electron microscopy indicated that the dominant morphology of H. trueperi calcium carbonate is spherulitic calcite with a fibrous radiated interior.In our own research, we isolated a biomineralizing thermophilic spore-forming bacterium from bark compost that has an optimum growth temperature of 60°C. Phylogenetic analysis of the 16S rRNA gene sequence identified the organism as Geobacillus thermoglucosidasius (8). Geobacillus spp. are a phenotypically and phylogenetically similar group of thermophilic bacilli (9). To date, we have found that G. thermoglucosidasius extracellularly catalyzes the formation of 100-m spheres and hexagonal crystals at 60°C in hydrogel containing sodium acetate, calcium chloride, and magnesium sulfate (calcite-promoting hydrogel). Microscopic analysis revealed that the minerals have polarizing properties and are thus highly crystallized. Under fluorescence microscopy, excitation occurred at 365 Ϯ 5, 480 Ϯ 20, and 545 Ϯ 15 nm, and broad-spectrum fluorescence was emitted with excitation at 350 nm. The maximum emitted wavelength was 446.9 nm for excitation at 369.6 nm. An X-ray diffraction analysis showed the crystals to be magnesium-calcite in the calcium carbonate group (8). From the observation that calcite was formed on both the interior and exterior of the G. thermoglucosidasius colony, we deduced that endospores constituted the nucleus of the calcites.The starvation for nitrogen and phosphate sources in calcitepromoting hydrogel promotes sporulation. In this study, we investiga...

Calcium carbonates: induced biomineralization with controlled macromorphology

“…Bacterial cells, especially spores with their high surface-to-volume ratio and specific cell wall structure, can serve as nucleation sites. Spores encapsulated by calcite might survive for long periods of time and can be reactivated, followed by the germination and growth of new bacterial generations (Murai and Yoshida, 2013). Hence, ample sporulation may explain differences in the amounts recorded between different strains of the genus Bacillus (Yasuda-Yasaki et al, 1978).…”

Calcium carbonates: Induced biomineralization vs. controlled macromorphology?

“…Bacterial cells, especially spores with their high surface to volume ratio and specific cell wall structure, can serve as nucleation sites. Spores encapsulated by calcite might survive for long periods of time, and can be reactivated, followed by germination and growth of new bacterial generations (Murai and Yoshida, 2013). Hence, ample sporulation may explain differences in the amounts recorded between different strains of the genus Bacillus (Yasuda-Yasaki et al, 1978).…”

Nested Formation of Calcium Carbonate Polymorphs in a Bacterial Surface Membrane with a Graded Nanoconfinement: An Evolutionary Strategy to Ensure Bacterial Survival

“…These techniques are complementary to characterize the biomolecular nanostructure (AFM), and the crystalline structure of the precipitated calcium carbonate polymorphs (HR-TEM), quantitatively. Usually, macroscale and mesoscopic methods such as IR, AFM, SEM, or X-ray spectroscopy and X-ray diffraction have been applied to characterize the bacterial cell membrane and its mineralization. − To our knowledge, only few publications addressed its biomineralization at the nanoscale. − …”