Fitting Mixotrophy into the Microbial Loop Paradigm: Advantages and Consequences of Mixotrophic Behavior Among Phagotrophic Algae

9508571碳的混合营养是异养和光营养在单一有机体中的结合。在单细胞微藻中，种类繁多的藻类摄取颗粒有机物质。吞噬藻类之间的混合营养行为存在几种可能的适应性优势。到目前为止，吞噬行为提供了三种一般策略：(1)主要是在高细菌丰度下的吞噬生长，当细菌丰度较低时，光营养是一种生长非常缓慢的机制；(2)主要是光营养生长，吞噬生长是在低光强下补充生长的机制；(3)主要是光营养生长，吞噬生长是获取主要营养物质如氮或磷的机制。这项研究将集中在吞噬微藻与纯粹的光养原生生物(藻类)和纯粹的异养原生生物(原生动物)竞争的能力。该框架包括一个模型，该模型将混合营养纳入一个简单的微生物食物网，以产生关于吞噬藻类与非吞噬藻类和原生动物竞争的能力的假设。该模型基于对混合营养行为的三种策略的理解。假说将在实验室通过连续培养中藻类、原生动物和吞噬藻类之间的一系列竞争实验来验证。实验将考察光照限制、添加易溶有机碳和无机营养限制对与非吞噬藻类和原生动物竞争的食性藻类生长的影响。指导性假设是，不同种类的吞噬藻类表现出的不同行为为它们提供了竞争优势，这将在特定情况下导致它们的成功。这些实验将确定这些情况，并为解释天然混合营养物种的分布提供有价值的见解。

9508571 Caron Mixotrophy is the combination of heterotrophic and phototrophic nutrition in a single organism. Among the unicellular microalgae, a wide variety of species ingest particulate organic material. Several possible adaptive advantages exist for mixotrophic behavior among phagotrophic algae. Thus far, three general strategies are served by phagotrophic behavior: (1) primarily phagotrophic growth at high bacterial abundances, with phototrophy serving as a mechanism for very slow grouth when bacteria are present at low abundances, (2) primarily phototrophic growth with phagotrophy serving as a mechanism for supplementing growth at low light intensities, and (3) primarily phototrophic growth with phagotrophy serving as a mechanism for acquiring major nutrients such as nitrogen or phosphorus. This research will focus on the ability of phagotrophic microalgae to compete with purely phototrophic protists (algae) and purely heterotrophic protists (protozoa). The framework includes a model that incorporates mixotrophy into a simple microbial food web in order to generate hypotheses concerning the ability of phagotrophic algae to compete with nonphagotrophic algae and protozoa. The model is based on the understanding of the three strategies for mixotrophic behavior. Hypotheses will be tested in the laboratory via a series of competition experiments between algae, protozoa, and phagotrophic algae in continuous cultures. Experiments will examine the effects of light limitation, additions of labile dissolved organic carbon, and inorganic nutrient limitation on the growth of phagotrophic algae competing with nonphagotrophic algae and protozoa. The guiding hypothesis is that the different behaviors exhibited by different species of phagotrophic algae provide them with a competitive advantage that will result in their success under particular circumstances. These experiments will establish those circumstances and provide valuable insights for explaining the distribution of mixotrophic species in na ture.