Giometto Andrea, Altermatt Florian, Maritan Amos, Stocker Roman, Rinaldo Andrea
Laboratory of Ecohydrology, School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland;
Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland; Institute of Evolutionary Biology and Environmental Studies, University of Zurich, CH-8057 Zurich, Switzerland;
Proc Natl Acad Sci U S A. 2015 Jun 2;112(22):7045-50. doi: 10.1073/pnas.1422922112. Epub 2015 May 11.
Phototaxis, the process through which motile organisms direct their swimming toward or away from light, is implicated in key ecological phenomena (including algal blooms and diel vertical migration) that shape the distribution, diversity, and productivity of phytoplankton and thus energy transfer to higher trophic levels in aquatic ecosystems. Phototaxis also finds important applications in biofuel reactors and microbiopropellers and is argued to serve as a benchmark for the study of biological invasions in heterogeneous environments owing to the ease of generating stochastic light fields. Despite its ecological and technological relevance, an experimentally tested, general theoretical model of phototaxis seems unavailable to date. Here, we present accurate measurements of the behavior of the alga Euglena gracilis when exposed to controlled light fields. Analysis of E. gracilis' phototactic accumulation dynamics over a broad range of light intensities proves that the classic Keller-Segel mathematical framework for taxis provides an accurate description of both positive and negative phototaxis only when phototactic sensitivity is modeled by a generalized "receptor law," a specific nonlinear response function to light intensity that drives algae toward beneficial light conditions and away from harmful ones. The proposed phototactic model captures the temporal dynamics of both cells' accumulation toward light sources and their dispersion upon light cessation. The model could thus be of use in integrating models of vertical phytoplankton migrations in marine and freshwater ecosystems, and in the design of bioreactors.
趋光性是指运动生物将其游动方向导向光源或远离光源的过程，它与关键的生态现象（包括藻华和昼夜垂直迁移）相关，这些现象塑造了浮游植物的分布、多样性和生产力，进而影响了水生生态系统中向更高营养级的能量转移。趋光性在生物燃料反应器和微生物推进器中也有重要应用，并且由于易于产生随机光场，它被认为是研究异质环境中生物入侵的一个基准。尽管趋光性在生态和技术方面具有相关性，但迄今为止，似乎还没有经过实验验证的趋光性通用理论模型。在这里，我们展示了绿藻眼虫在受控光场下行为的精确测量结果。对眼虫在广泛光强范围内的趋光性聚集动态进行分析表明，经典的凯勒 - 西格尔趋化数学框架只有在通过广义“受体定律”对趋光敏感性进行建模时，才能准确描述正向和负向趋光性，广义“受体定律”是一种对光强的特定非线性响应函数，它驱使藻类趋向有利的光照条件并远离有害条件。所提出的趋光模型捕捉了细胞向光源聚集的时间动态以及光照停止后它们的分散情况。因此，该模型可用于整合海洋和淡水生态系统中浮游植物垂直迁移的模型，以及生物反应器的设计。
