Institut national de la Recherche scientifique, Centre Eau Terre Environnement 490 de la Couronne , Québec , (Québec) Canada G1K 9A9.
Environ Sci Technol. 2018 Jul 17;52(14):7988-7995. doi: 10.1021/acs.est.8b01408. Epub 2018 Jun 27.
In this study we tested the hypothesis that metal uptake by unicellular algae may be affected by changes in metal speciation in the boundary layer surrounding the algal cells. The freshwater alga Chlamydomonas reinhardtii was preacclimated to different N nutrition regimes; changes in N nutrition are known to change the nature of extracellular metabolites (e.g., reactive oxygen species "ROS", and OH) and thus boundary layer chemical conditions. Specifically, at a constant bulk free Cd concentration, Cd uptake by N-starved algae in cysteine-buffered solution was significantly higher than that in NTA-buffered solution. This enhancement was likely due to an increase of the free Cd concentration in the boundary layer, resulting from localized cysteine oxidation by ROS released from these algae. On the other hand, Cd uptake was markedly lower when the free Cd concentration near cell surface decreased as a result of an increase in the boundary layer pH of nitrate-acclimated algae or enhanced localized metal complexation. The results imply that redox, acid-base and metal complexation processes in the boundary layer differ from those in bulk water, even under chemically stable bulk conditions, and the boundary layer effect may well be of significance to phytoplankton acquisition of other trace metals.
在这项研究中，我们检验了这样一个假设，即单细胞藻类对金属的摄取可能会受到围绕藻类细胞的边界层中金属形态变化的影响。我们将淡水藻类莱茵衣藻预先适应于不同的氮营养条件；众所周知，氮营养的变化会改变细胞外代谢物的性质（例如，活性氧“ROS”和 OH），从而改变边界层的化学条件。具体来说，在恒定的游离 Cd 浓度下，在半胱氨酸缓冲溶液中饥饿氮处理的藻类对 Cd 的摄取明显高于 NTA 缓冲溶液。这种增强可能是由于边界层中游离 Cd 浓度的增加所致，这是由于这些藻类释放的 ROS 局部氧化半胱氨酸所致。另一方面，当硝酸盐适应藻类的边界层 pH 值增加或局部金属络合增强导致细胞表面附近的游离 Cd 浓度降低时，Cd 的摄取明显降低。结果表明，即使在化学稳定的条件下，边界层中的氧化还原、酸碱和金属络合过程也与主体水中的这些过程不同，边界层效应很可能对浮游植物获取其他痕量金属具有重要意义。
