Department of Marine Sciences, University of Gothenburg, Göteborg, Sweden.
Department of Marine Sciences, University of Gothenburg, Göteborg, Sweden.
Aquat Toxicol. 2020 Sep;226:105551. doi: 10.1016/j.aquatox.2020.105551. Epub 2020 Jul 3.
Strains of microalgae vary in traits between species and populations due to adaptation or stochastic processes. Traits of individual strains may also vary depending on the acclimatization state and external forces, such as abiotic stress. In this study we tested how metal tolerance differs among marine diatoms at three organizational levels: species, populations, and strains. At the species level we compared two pelagic Baltic Sea diatoms (Skeletonema marinoi and Thalassiosira baltica). We found that the between-species differences in tolerance (EC50) to the biologically active metals (Cu, Co, Ni, and Zn) was similar to that within-species. In contrast, the two species differed significantly in tolerance towards the non-essential metals, Ag (three-fold higher in T. baltica), Pb and Cd (two and three-fold higher in S. marinoi). At the population level, we found evidence that increased tolerance against Cu and Co (17 and 41 % higher EC50 on average, respectively) had evolved in a S. marinoi population subjected to historical mining activity. On a strain level we demonstrate how the growth phase of cultures (i.e., cellular densities above exponential growth) modulated dose-response relationships to Ag, Cd, Co, Cu, and Zn. Specifically, the EC50's were reduced by 10-60 % in non-exponentially growing S. marinoi (strain RO5AC), depending on metal. For the essential metals these differences were often larger than the average differences between the two species and populations. Consequently, without careful experimental design, interactions between nutrient limitation and metal stress may interfere with detection of small, but evolutionary and ecologically important, differences in tolerance between microalgae. To avoid such artifacts, we outline a semi-continuous cultivation approach that maintains, and empirically tests, that exponential growth is achieved. We argue that such an approach is essential to enable comparison of population or strain differences in tolerance using dose-response tests on cultures of microalgae.
由于适应或随机过程，微藻菌株在物种和种群之间的特征上存在差异。个体菌株的特征也可能因适应状态和外部力量（如非生物胁迫）而有所不同。在这项研究中，我们测试了海洋硅藻在三个组织水平上的金属耐受性差异：物种、种群和菌株。在物种水平上，我们比较了两种波罗的海浮游硅藻（Skeletonema marinoi 和 Thalassiosira baltica）。我们发现，对生物活性金属（Cu、Co、Ni 和 Zn）的耐受性（EC50）在物种间的差异与种内相似。相比之下，这两个物种对非必需金属的耐受性差异显著，Ag（在 T. baltica 中高出三倍）、Pb 和 Cd（在 S. marinoi 中高出两倍和三倍）。在种群水平上，我们发现证据表明，在一个受到历史采矿活动影响的 S. marinoi 种群中，对 Cu 和 Co 的耐受性增加了（平均 EC50 分别高出 17%和 41%）。在菌株水平上，我们展示了培养物的生长阶段（即细胞密度高于指数生长）如何调节对 Ag、Cd、Co、Cu 和 Zn 的剂量-反应关系。具体来说，在非指数生长的 S. marinoi（RO5AC 菌株）中，EC50 降低了 10-60%，具体取决于金属。对于必需金属，这些差异通常大于两个物种和种群之间的平均差异。因此，如果实验设计不当，营养限制和金属胁迫之间的相互作用可能会干扰对微藻之间耐受性的小但具有进化和生态重要性的差异的检测。为了避免这种假象，我们概述了一种半连续培养方法，该方法可维持并通过经验测试实现指数生长。我们认为，这种方法对于使用微藻培养物的剂量-反应试验来比较种群或菌株之间的耐受性差异是必不可少的。
