Centre Eau Terre Environnement , Institut national de la Recherche scientifique , 490 de la Couronne , Québec , Québec G1K 9A9 , Canada.
Key Laboratory of the Coastal and Wetland Ecosystems, Ministry of Education, College of Environment and Ecology , Xiamen University , Xiamen , Fujian 361102 , China.
Environ Sci Technol. 2019 Jun 4;53(11):6511-6519. doi: 10.1021/acs.est.9b00571. Epub 2019 May 23.
Low-molecular-weight weak ligands such as cysteine have been shown to enhance metal uptake by marine phytoplankton in the presence of strong ligands, but the effect is not observed in freshwater. We hypothesized that these contrasting results might be caused by local cysteine degradation and a Ca effect on metal-ligand exchange kinetics in the boundary layer surrounding the algal cells; newly liberated free metal ions cannot be immediately complexed in seawater by Ca-bound strong ligands but can be rapidly complexed by free ligands at low-Ca levels. The present results consistently support this hypothesis. At constant bulk Cd concentrations, buffered by strong ligands: (1) at 50 mM Ca, cysteine addition significantly enhanced Cd uptake in high-Ca preacclimated euryhaline Chlamydomonas reinhardtii (cultured with cysteine as a nitrogen source to enhance local Cd liberation via cysteine degradation); (2) at 0.07 mM Ca, this enhancement was not observed in the algae; (3) at 50 mM Ca, the enhancement disappeared when C. reinhardtii were cultured with ammonium (to inhibit cysteine degradation and local Cd liberation); (4) cysteine addition did not enhance Cd uptake by cysteine-cultured marine Thalassiosira weissflogii when the concentration of immediately reacting strong ligands was sufficient to complex local Cd liberation.
低分子量弱配体，如半胱氨酸，已被证明在强配体存在的情况下增强海洋浮游植物对金属的吸收，但在淡水中则观察不到这种作用。我们假设这些对比结果可能是由于边界层中半胱氨酸的局部降解以及 Ca 对金属-配体交换动力学的影响；新释放的游离金属离子不能立即与 Ca 结合的强配体在海水中形成配合物，但可以在低 Ca 水平下迅速与游离配体形成配合物。目前的结果一致支持这一假设。在恒定的 Cd 总浓度下，用强配体缓冲：（1）在 50 mM Ca 下，半胱氨酸的添加显著增强了高 Ca 预驯化的广盐性衣藻（用半胱氨酸作为氮源培养以通过半胱氨酸降解增强局部 Cd 释放）中 Cd 的吸收；（2）在 0.07 mM Ca 下，藻类中则没有观察到这种增强；（3）在 50 mM Ca 下，当衣藻用铵盐（抑制半胱氨酸降解和局部 Cd 释放）培养时，这种增强作用消失；（4）当立即反应的强配体浓度足以与局部 Cd 释放形成配合物时，半胱氨酸添加并未增强用半胱氨酸培养的海洋拟菱形藻对 Cd 的吸收。
