梭菌对含镁方解石形态的控制及其可能机理

在 Mg/Ca 摩尔比为 4∶1 的 Lagoa Vermelha 培养基中对一株分离自青海湖底沉积物的梭菌 SN-1（Clostridium sp.）进行了为期 55 d 的碳酸盐矿物培养实验，同时还完成了一组无菌对照实验。利用扫描电子显微镜对沉淀物进行了系统的观察，用 X- 射线衍射仪对沉淀物的矿物成分进行了测定。结果表明：（1）SN-1 可以促进特殊形态含镁方解石的形成，而无菌对照实验产物中仅见不规则状的碳酸盐矿物；（2）特殊形态的含镁方解石可能是在细菌表面成核和生长的结果，它们的演化趋势是（杆状）→哑铃形→花菜状→球形。作者认为这是因为梭菌两端的带负电基团比菌体中间丰富，易聚集更多的 Ca²⁺和 Mg²⁺，Ca²⁺和 Mg²⁺离子作为“阳离子桥”吸引 CO32-，其结果是两端的晶体生长相对较快、中间生长相对较慢，进而形成哑铃形含镁方解石；“哑铃”继续生长，其两端会长成两个“花菜”或半球；若两个半球相接并闭合则发展为球状矿物。

Clostridium sp.Controlled Morphology of Mg-bearing calcite and its Implication for Possible Mechanism

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.