Journal of Microbial & Biochemical Technology

Abstract

Effect of Doping with Metals, Silicate, And Phosphate Ions on Fluorescence Properties and Morphology of Calcite Single Crystals Synthesized in Geobacillus thermoglucosidasius Parent Colonies

Rie Murai and Naoto Yoshida

Geobacillus thermoglucosidasius cells grown on nutrient agar medium (parent colony) were placed on the surface of a calcite-promoting hydrogel containing acetate and calcium. After incubation at 60°C for 4 days, calcite single crystals of 110-130 μm in diameter were synthesized within the parent colony. The calcite contained 6.6% (atom%) Mg and showed striking fluorescent properties. Changes in the morphology and development of fluorescence intensity of calcite synthesized on calcite-promoting hydrogel doped with different metal ions, silicate ion, and phosphate ion were investigated. Doping with Mg, P, or Sr ions yielded calcite lattices with the respective metal ions substitutionally dissolved into calcium sites. On calcite-promoting hydrogel containing 2 mM Mg ion, the calcite Mg content increased to 22 atom%. Doping of the hydrogel with Al, Si, or P ions yielded calcites with increased fluorescence intensity (190-196% of that of control calcites). Contrary to expectations, doping of the hydrogel with Mn, Sr, Fe, or Co ions yielded calcites with decreased fluorescence intensity (64.4-96.9% of that of control calcites). When the hydrogel was doped with Mg or P ions, the calcite surface became smooth or sheet-like, respectively, in contrast to the rough-surfaced spherical morphology of control calcites. Distinctive crevice structures were observed on the surfaces of calcites synthesized on hydrogel doped with Mn or Al ions. Fluorescence microscopy showed that calcites emitted blue, green, or red fluorescence when illuminated with light at wavelengths of 360-370, 460- 500, or 530-560 nm, respectively. Calcites synthesized on hydrogel doped with Al, Si, and P ions emitted stronger fluorescence than control calcites when illuminated with light at 360-370 nm. Our studies have demonstrated that G. thermoglucosidasius is useful for the preparation of calcite phosphors in the absence of rare earth elements.