Abstract
Fresh Geobacillus thermoglucosidasius cells grown on soybean-casein digest nutrient agar were inoculated as a parent colony 1cm in diameter on the surface of an agar gel containing acetate and calcium ions (calcite-promoting hydrogel) and incubated at 60°C for 4days, after which magnesium-calcite single crystals of 50-130µm in size formed within the parent colony. Addition of EDTA, polyacrylic acid or N,N-dicyclohexylcarbodiimide to the calcite-forming hydrogel inhibited the parent colony from forming magnesium-calcite crystals. Inoculation of G. thermoglucosidasius on calcite-forming hydrogel containing 5µM cadmium and 20µM zinc resulted in a decrease in the sporulation rate from 55 to 7-8%. Magnesium-calcite synthesis decreased relative to the sporulation rate. G. thermoglucosidasius exhibited higher adsorption/absorbance of calcium than other Geobacillus sp. that do not mediate calcite formation and higher levels of magnesium accumulation. Calcium ions contained in the calcite-promoting hydrogel and magnesium ions concentrated in G. thermoglucosidasius cells serve as the elements for magnesium-calcite synthesis. The observed decreases in sporulation rate and magnesium-calcite formation support the hypothesis that endospores act as nuclei for the synthesis of magnesium-calcite single crystals.
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