微生物胞外多糖的合成及其在重金属修复中的作用机制与应用

重金属的生物不可降解性使其在环境中长期存在,导致严重的环境污染,对人类健康和生态系统构成威胁。与传统的物化修复技术相比,微生物修复具有成本低廉、环境友好和高效等特点。在面对重金属胁迫或营养不均衡时,微生物会被激发以分泌合成胞外多糖(exopolysaccharides, EPS)。由此可见,EPS的产生是微生物对抗重金属胁迫的重要策略之一。EPS不仅能保护微生物在低温、高温、高盐等极端环境或受毒性化合物胁迫的条件下存活,并且在细胞内外进行信息和物质的交流与传递,既作为保护屏障限制重金属离子进入细胞,又作为介质进行交流。EPS结构中含有多个带负电荷的官能团,能够与重金属离子发生络合、离子交换、氧化还原等反应,从而降低重金属的生物有效性并减轻其毒性。微生物EPS在重金属胁迫环境中的修复具有重要意义。然而,目前缺乏关于微生物EPS合成过程、与重金属互作机制及其在重金属胁迫环境中应用现状的系统综述。本文概述了微生物EPS及其分类,详细阐述了细菌EPS胞内及胞外的生物合成机制,并探讨了微生物EPS与重金属互作机制,以及微生物EPS修复水、土环境中重金属污染方面的研究进展。最后,展望了EPS合成及其在重金属修复中的作用机制研究,可为微生物EPS进一步应用于环境重金属污染修复提供支持。

Synthesis of microbial exopolysaccharides and their mechanisms and applications in heavy metal remediation

The non-biodegradable nature of heavy metals (HMs) results in their long-term presence in the environment, leading to severe environmental pollution and posing a threat to human health and ecosystems. Compared with physical and chemical remediation techniques, microbial remediation is praised for the low cost, environmental friendliness, and high efficiency. When facing heavy metal stress or nutrient imbalance, microorganisms are stimulated to produce and secrete extracellular polysaccharides (EPSs). Therefore, the production of EPSs is regarded as one of the important strategies employed by microorganisms to combat HM stress. EPSs not only protect microorganisms in extreme conditions such as low temperature, high temperature, high salinity, or exposure to toxic compounds but also facilitate the communication and transfer of information and substances both inside and outside the cells. EPSs serve as a protective barrier to restrict the entry of HM ions into the cells and as a medium for communication. EPSs contain multiple negatively charged functional groups capable of complexing with HM ions, undergoing ion exchange, and participating in redox reactions, thereby reducing the bioavailability and toxicity of HMs. Microbial EPSs play a significant role in the remediation of HM-contaminated environments. However, there is currently a lack of a systematic review on the synthesis process of microbial EPSs, the mechanisms of the interaction of EPSs with HMs, and the application status of EPSs in the environments with HM stress. This article provides an overview of microbial EPSs and their classification, elaborates on the intracellular and extracellular biosynthesis mechanisms of bacterial EPSs, explores the interactions between microbial EPSs and HMs, and discusses research advances in the use of microbial EPSs for the remediation of HM pollution in water and soil environments. Finally, it looks ahead to the synthesis of EPSs and the role of EPSs in HM remediation, offering support for the further application of microbial EPSs in the remediation of environmental HM pollution.