Abstract:

In  this study, culture experiments of carbonate precipitation using Lagoa Vermelha medium with 4:1 molar Mg/Ca ratio within 55 days were made under  the mediation of Clostridium sp.  (SN-1)  from Qinghai Lake sediment. At  the same  time, aseptic experiments were carried as control. The morphologies of precipitated carbonates at different  incubation  times were observed by using scanning electron microscopy, and mineral species were determined by X-ray diffraction. The results showed that (1) SN-1 helped promote the formation of Mg-bearing calcites with special shapes, but only irregular carbonate minerals were formed in the aseptic experiments, and (2) specifically shaped Mg-bearing calcite might nucleate and grow on the cell surfaces of bacteria, and  then evolve  from rod-like  to dumbbell-like, cauliflower-like and spherulite shapes. The authors suggest  that  this  is because more negative ionic groups concentrated on the polar ends than on the middle parts of rod-shaped bacteria, resulting in attracting more Ca2+ and Mg2+on both polar ends of bacterial cells. Ca2+ and Mg2+serve as “cation bridge”  to allure CO32-from the microenvironment. Consequently, rapid nucleation and growth on  the polar ends of  the cells  leads  to development of crystal bundles. When  the dumbbell-like calcitecontinues  to grow,  the  two  lobes of  the dumbbell would grow  into  two cauliflowers or hemispheres. The two hemispheres would merge together to form a spherulite, if both hemispheres could continue to grow.

Key words: Clostridium sp., dumbbell-like morphology, spherical morphology, Mg-bearing calcite, mechanism