1 Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, USA.
2 School of the Earth, Ocean, and Environment, University of South Carolina, Columbia, SC, USA.
Appl Spectrosc. 2019 Mar;73(3):304-312. doi: 10.1177/0003702818812090. Epub 2018 Nov 15.
Phytoplankton play a vital role as primary producers in aquatic ecosystems. One common approach to classifying phytoplankton is fluorescence excitation spectroscopy, which leverages the variation in types and concentrations of pigments among different phytoplankton taxonomic groups. Here, we used a fluorescence imaging photometer to measure excitation ratios ("signatures") of single cells and bulk cultures of seven differently pigmented phytoplankton species as they progressed from nitrogen N-replete to N-depleted conditions. Our objective was to determine whether N depletion alters the fluorescence excitation signature of each species and, if so, how quickly they recover when N (as nitrate) was resupplied, because these factors affect our ability to classify the species correctly. Of the seven species studied, only Proteomonas sulcata, a marine cryptophyte, showed measurable changes in single-cell fluorescence excitation ratios and bulk fluorescence excitation spectra. These changes were likely due to decreases in the cellular concentration of phycoerythrin, a N-rich pigment, as N became scarce. Within 3 h of resupply of N, fluorescence signatures began returning to pre-depletion values and were indistinguishable from N-replete cells by 80 h after resupply. These data suggest that our classification approach is robust for non-PE containing phytoplankton. PE-containing phytoplankton might exhibit systematic changes in their signatures depending on their level of N depletion, but this could be detected and the phytoplankton re-classified following a few hours of incubation in N replete conditions.
浮游植物在水生生态系统中作为初级生产者起着至关重要的作用。一种常见的浮游植物分类方法是荧光激发光谱法，该方法利用不同浮游植物分类群中色素的类型和浓度的变化。在这里，我们使用荧光成像光度计来测量七种不同色素的浮游植物单细胞和批量培养物在从氮 N 充足到 N 缺乏条件下的激发比（“特征”）。我们的目的是确定 N 缺乏是否会改变每种物种的荧光激发特征，如果是这样，当 N（作为硝酸盐）重新供应时，它们恢复的速度有多快，因为这些因素会影响我们正确分类物种的能力。在研究的七种物种中，只有海洋 cryptophyteProteomonas sulcata 表现出单细胞荧光激发比和批量荧光激发光谱的可测量变化。这些变化可能是由于 N 变得稀缺时，富含 N 的色素藻红蛋白的细胞浓度降低所致。在 N 重新供应后的 3 小时内，荧光特征开始恢复到缺氮前的值，并且在重新供应后 80 小时与氮充足的细胞无法区分。这些数据表明，我们的分类方法对于不含 PE 的浮游植物是稳健的。含有 PE 的浮游植物的特征可能会根据其 N 缺乏程度发生系统变化，但可以在富含 N 的条件下孵育几个小时后检测到并重新分类浮游植物。
