镉胁迫对屎肠球菌CX2-6生理代谢及胞外多糖合成的影响

Effect of Cd stress on physiological metabolism and exopolysaccharide synthesis of Enterococcus faecalis CX2-6

过量合成胞外多糖是微生物在抵御外界不良环境时重要的应激手段,探索不同胁迫条件对微生物合成胞外多糖的影响对于理解微生物应激代谢至关重要.本研究对屎肠球菌CX2-6所产胞外多糖进行分离纯化和初步结构解析,进而探索了镉胁迫对屎肠球菌CX2-6生理代谢及其产胞外多糖结构的影响,并采用动力学模型探索了不同多糖对镉吸附性能的差异.结果表明,CX2-6所产胞外多糖主要单糖组成为葡萄糖、甘露糖等,且由3个单一组分构成,其中,含量较高的EPS-1组分为粗糙的片状,而EPS-2组分为不规则扭曲的片状.镉胁迫下屎肠球菌CX2-6胞外多糖产量明显增加,其中,培养基中镉浓度为200 mg·L^(-1)时胞外多糖产量最高,达到1110.89 mg·g^(-1),较胁迫前增加了51.71%,且此时胞外多糖对镉的吸附能力最高.镉胁迫条件下所产生的胞外多糖对镉的吸附能力显著提高,且其吸附过程符合二级动力学,其中,Langmuir等温模型可以更好地拟合胞外多糖对重金属镉的吸附.综上所述,屎肠球菌CX2-6所产生的胞外多糖对重金属离子具有良好的吸附作用,并且在镉胁迫下胞外多糖的产量和吸附性能明显增加,这一特性使得该胞外多糖在重金属污染防治领域显示出巨大的应用前景.

Excessive synthesis of exopolysaccharides(EPS)is a crucial stress response mechanism employed by microorganisms to withstand adverse environments.Investigating the impact of different stress conditions on EPS synthesis is essential for comprehending microbial stress metabolism.In this study,EPS produced by Enterococcus faecalis CX2-6 was purified and partially characterized,and the effects of Cd stress on the physiological metabolism,EPS structure,and Cd adsorption performance of CX2-6 were investigated.Our findings revealed that the EPS produced by CX2-6 primarily contain glucose and mannose,among other monosaccharides.After purified by column chromatography,it was found that EPS produced by CX2-6 can be divided into three components,with component 1 exhibiting a higher content and a rough plate-like shape,while component 2 displays an irregular twisted plate-like shape.Under Cd stress,both the production and Cd adsorption capacity of EPS from CX2-6 significantly increased.The highest EPS yield was observed at 1110.89 mg·g^(-1) when the Cd concentration in the culture medium reached 200 mg·L^(-1),representing a 51.71%increase compared to the control group.Moreover,the EPS exhibited the highest adsorption capacity for Cd at this concentration.Scanning Electron Microscopy(SEM)analysis clearly demonstrated a significant increase in the amount of sticky substances on the surface of CX2-6 after Cd stress,accompanied by a notable rise in the relative abundance of functional groups such as—OH,C=O,and C—O on the bacterial surface.The adsorption process of EPS for Cd followed a second-order kinetics model,and the Langmuir isotherm model provided a better fit for the adsorption process.In conclusion,the EPS produced by Enterococcus faecalis CX2-6 possess excellent adsorption properties for heavy metal ions,with their production and adsorption capacity being significantly enhanced under cadmium stress.This characteristic renders EPS a promising tool for application in the field of heavy metal pollution control.