College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China.
Demonstration Laboratory of Element and Life Science Research, Laboratory Centre of Life Science, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China.
Sci Total Environ. 2023 May 1;871:161995. doi: 10.1016/j.scitotenv.2023.161995. Epub 2023 Feb 3.
Extracellular polymeric substances (EPS) form an interface between microalgae and the surrounding water environment. Copper (Cu) and zinc (Zn) are essential micronutrients but may negatively affect microbial growth when their concentrations reach toxic thresholds. However, how EPS affect the accumulation and resistance of Cu and Zn in microalgae remains largely unknown. Here, we investigated EPS production upon Cu/Zn exposure and compared the tolerance strategies to the two metals by Chlamydomonas reinhardtii with and without EPS. Microalgal EPS synthesis was induced by Cu/Zn treatments, and the functional groups of polysaccharides and proteins were involved in complexation with metal ions. The extraction of EPS aggravated the toxicity and reduced the removal of metals from solution, but the effect was more pronounced for Cu than for Zn. Copper bound on the cell surface accounted for 54.6 ± 2.0 % of the Cu accumulated by C. reinhardtii, whose EPS components strongly correlated with Cu adsorption. In contrast, 74.3 ± 3.0 % of accumulated Zn was absorbed in cells, and glutathione synthesis was significantly induced. Redundancy and linear correlation analyses showed that the polysaccharide, protein and DNA contents in EPS were significantly correlated with Cu accumulation, absorption and adsorption but not with Zn. Data fitted to a Michaelis-Menten model further showed that the EPS-intact cells had higher binding capacity for Cu but not for Zn. These differential impacts of EPS on Cu/Zn sorption and detoxification contribute to a more comprehensive understanding of the roles of microalgal EPS in the biogeochemical cycle of metals.
细胞外聚合物（EPS）在微藻与周围水环境之间形成了一个界面。铜（Cu）和锌（Zn）是必需的微量元素，但当其浓度达到毒性阈值时，可能会对微生物的生长产生负面影响。然而，EPS 如何影响微藻对 Cu 和 Zn 的积累和抗性仍知之甚少。在这里，我们研究了 Cu/Zn 暴露时 EPS 的产生，并比较了有/无 EPS 的莱茵衣藻对这两种金属的耐受策略。Cu/Zn 处理诱导了微藻 EPS 的合成，多糖和蛋白质的功能基团参与了与金属离子的络合。EPS 的提取加剧了毒性并降低了金属从溶液中的去除率，但对 Cu 的影响比 Zn 更明显。Cu 结合在细胞表面，占莱茵衣藻积累的 Cu 的 54.6±2.0%，其 EPS 成分与 Cu 吸附强烈相关。相比之下，74.3±3.0%的积累 Zn 被细胞吸收，谷胱甘肽合成明显受到诱导。冗余和线性相关分析表明，EPS 中的多糖、蛋白质和 DNA 含量与 Cu 的积累、吸收和吸附显著相关，但与 Zn 不相关。拟合 Michaelis-Menten 模型的数据进一步表明，完整 EPS 的细胞对 Cu 具有更高的结合能力，但对 Zn 没有。EPS 对 Cu/Zn 吸附和解毒的这些差异影响有助于更全面地了解微藻 EPS 在金属生物地球化学循环中的作用。
