镉胁迫下泡菜乳酸乳球菌的形态变化

通过扫描电镜和透射电镜分别观察不同质量浓度水平的Cd2+对泡菜乳酸乳球菌(Lactococcus lactis subsp.lactis)细胞的影响,扫描电镜结果显示:Cd2+质量浓度在0、10 mg/L时,泡菜乳酸乳球菌呈椭圆形、表面光滑、菌体生长繁殖旺盛,随着Cd2+质量浓度的增加菌体细胞表面产生白色颗粒状物质、菌体细胞存活数量大幅下降(OD600 nm值由1.336下降到0.515)。当添加200 mg/L Cd2+时,几乎没有见到明显的菌体、显示有少量棱形晶状物。透射电镜结果显示:当Cd2+质量浓度为0~50 mg/L时泡菜乳酸乳球菌结构完整、细胞内容物分布均、菌体生长较为正常,当菌体暴露于100、200 mg/L Cd2+时菌体细胞出现异常现象,如细胞破裂、内容物从薄膜穿孔中释放、质壁分离等。两类电镜结果均表明:在低质量浓度Cd2+(≤50 mg/L)胁迫下,对泡菜乳酸乳球菌的生长几乎不产生影响,添加Cd2+质量浓度上升到100、200 mg/L时泡菜乳酸乳球菌正常生长受到抑制。

Morphological Change of Lactococcus lactis subsp.lactis under Cadmium Stress

Using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the effects of different
levels of cadmium (Cd2 +) on Lactococcus lactis subsp. lactis cells were examined. The SEM results showed that when the
mass concentration of Cd2+ was 0 and 10 mg/L, the bacterium displayed an oblong shape with smooth surface and grew
vigorously. With increasing concentration of Cd2+, white granules appeared on the surface and the number of surviving cells
began to fall (i.e., OD was reduced from 1.336 to 0.515). Under the stress of Cd2+ at 200 mg/L, almost no visible bacteria
were seen and a small amount of prismatic crystals appeared. The TEM results revealed that when the mass concentration
of Cd2+ was 0–50 mg/L, the cell structure of this strain was intact and the cellular contents were evenly distributed, and the
strain grew normally. When exposed to 100 and 200 mg/L Cd2+, it began to change abnormally such as ruptured cells and
release of cellular contents from holes in the cellular membrane. In addition, plasmolysis was observed. Together, these
results indicated that Lactococcus lactis subsp. lactis was hardly affected by Cd2+ at low concentrations (≤ 50 mg/L) but
inhibited at high concentrations (100 and 200 mg/L).