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Why Does Cysteine Enhance Metal Uptake by Phytoplankton in Seawater but Not in Freshwater?
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2019-05-23 , DOI: 10.1021/acs.est.9b00571 Fengjie Liu 1 , Qiao-Guo Tan 2 , Claude Fortin 1 , Peter G. C. Campbell 1
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2019-05-23 , DOI: 10.1021/acs.est.9b00571 Fengjie Liu 1 , Qiao-Guo Tan 2 , Claude Fortin 1 , Peter G. C. Campbell 1
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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 Cd2+ 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 Cd2+ 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 Cd2+ 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 Cd2+ liberation.
中文翻译：
半胱氨酸为何能增加浮游植物在海水中而不是在淡水中对金属的吸收？
在强配体存在下，低分子量弱配体（例如半胱氨酸）已显示出可增强海洋浮游植物对金属的吸收，但在淡水中未观察到这种作用。我们假设这些相反的结果可能是由于半胱氨酸的局部降解以及钙对藻细胞周围边界层中金属-配体交换动力学的影响所致。新释放的自由金属离子不能立即在海水中被钙结合的强配体络合，但可以被低钙水平的自由配体快速络合。目前的结果一致支持这一假设。在恒定的大量Cd 2+浓度下，通过强配体缓冲：（1）在50 mM Ca下，半胱氨酸的添加显着提高了高Ca预适应的淡水胆碱对Cd的吸收。莱茵衣藻（以半胱氨酸为氮源培养，以通过半胱氨酸降解增强局部Cd 2+的释放）；（2）在0.07 mM Ca下，在藻类中未观察到这种增强；（3）在50 mM Ca下，将莱茵衣藻与铵盐一起培养（抑制半胱氨酸降解和Cd 2+的局部释放）时，增强作用消失。（4）当立即反应的强配体浓度足以使局部Cd 2+释放复杂化时，添加半胱氨酸并不能提高半胱氨酸培养的海洋Thalassiosira weissflogii对Cd的吸收。
更新日期：2019-05-24
中文翻译：
半胱氨酸为何能增加浮游植物在海水中而不是在淡水中对金属的吸收？
在强配体存在下，低分子量弱配体（例如半胱氨酸）已显示出可增强海洋浮游植物对金属的吸收，但在淡水中未观察到这种作用。我们假设这些相反的结果可能是由于半胱氨酸的局部降解以及钙对藻细胞周围边界层中金属-配体交换动力学的影响所致。新释放的自由金属离子不能立即在海水中被钙结合的强配体络合，但可以被低钙水平的自由配体快速络合。目前的结果一致支持这一假设。在恒定的大量Cd 2+浓度下，通过强配体缓冲：（1）在50 mM Ca下，半胱氨酸的添加显着提高了高Ca预适应的淡水胆碱对Cd的吸收。莱茵衣藻（以半胱氨酸为氮源培养，以通过半胱氨酸降解增强局部Cd 2+的释放）；（2）在0.07 mM Ca下，在藻类中未观察到这种增强；（3）在50 mM Ca下，将莱茵衣藻与铵盐一起培养（抑制半胱氨酸降解和Cd 2+的局部释放）时，增强作用消失。（4）当立即反应的强配体浓度足以使局部Cd 2+释放复杂化时，添加半胱氨酸并不能提高半胱氨酸培养的海洋Thalassiosira weissflogii对Cd的吸收。
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