Phosphonate Utilization by Eukaryotic Phytoplankton: Who, How, and Where?

磷(P)是所有活细胞必需的营养物质。它是遗传物质和细胞膜的核心组成部分，是能量产生和调节酶活性的组成部分。在海洋环境中，磷以无机（Pi）和溶解有机（DOP）形式存在；这些不同形态磷的有效性和浓度是海洋浮游植物生长的重要控制因素。海洋浮游植物是单细胞光合生物，既可以是原核细菌，也可以是真核植物。虽然Pi是海洋浮游植物首选的磷形式，但在海洋的大部分地区，它的含量非常低，限制了浮游植物的生长。在这些地区，DOP是最重要的P源。DOP池的组成一般可分为两大类：P酯类和磷酸盐类。所有的海洋浮游植物都能够利用P酯来支持生长；相比之下，迄今为止，磷酸盐仅被证明是细菌营养中磷的重要来源。本项目将确定海洋真核浮游植物利用磷酸盐作为生长磷源的能力。基因组分析将确定真核浮游植物物种对磷酸盐生长的代谢反应，以及自然种群使用磷酸盐的相关性。了解控制海洋养分循环的浮游植物的代谢能力是至关重要的。此外，该项目对了解海洋变化对浮游植物生长的潜在影响具有重要价值。该项目为当地社区大学的本科生提供了研究机会，并为一个为不同学生群体服务的课后项目提供了实践丰富项目。磷酸盐占海洋有机磷库的10%，已被证明是一个动态的有机磷库，可被海洋光合细菌吸收和产生。真核浮游植物以磷酸盐补充其生长的能力仍未得到广泛的探索。一些真核浮游植物已被证明使用草甘膦（一种化学合成的除草剂膦酸盐）作为磷源；目前尚不清楚开放海洋真核浮游植物是否可以利用海洋环境中天然存在的磷酸盐。初步实验表明，至少有一些真核浮游植物能够直接利用细胞外磷酸盐。该项目描述了真核浮游植物谱系中磷酸盐利用的普遍性，并确定了支持自然发生的磷酸盐获取和生长的细胞基础。除了系统发育分析外，该项目还使用全细胞转录组学和功能基因互补分析来了解磷酸盐的生物利用度以及天然真核浮游植物种群对磷酸盐利用的相关性。了解控制海洋生物地球化学循环的浮游植物的代谢能力至关重要。考虑到未来海洋可能变得更加分层的预测，这一点尤其重要，这可能会增加包括膦酸盐在内的DOP在支持浮游植物生长方面的重要性。

Phosphorus (P) is an essential nutrient for all living cells. It is a central component of genetic material and cellular membranes and is integral to energy production and regulating enzyme activity. In the marine environment, P occurs as inorganic (Pi) and dissolved organic (DOP) forms; the availability and concentration of these different forms of P is an important control on marine phytoplankton growth. Marine phytoplankton are single-celled photosynthetic organisms and can be both prokaryotic bacteria and eukaryotic plants. While Pi is the preferred form of P for marine phytoplankton, in large regions of the oceans it is at such low levels that it restricts phytoplankton growth. In these regions, DOP is the most important P source. The composition of the DOP pool can generally be divided into two major groups: P esters and phosphonates. All marine phytoplankton are capable of using P esters to support growth; in contrast, phosphonates have only been shown to be an important source of P in the nutrition of bacteria to date. This project will determine the ability of marine eukaryotic phytoplankton to use phosphonates as a source of P for growth. Genomic analyses will determine the metabolic response of eukaryotic phytoplankton species to growth on phosphonates as well as the relevance of phosphonate use by natural populations. It is critical to understand the metabolic capabilities of phytoplankton which control marine nutrient cycling. In addition, the project is of great value in understanding the potential impacts of a changing ocean on phytoplankton growth. The project supports reseach opportunities for undergraduates from a local community college as well as hands-on enrichment programs for an afterschool program that serves a diverse student population. Comprising up to 10% of the marine DOP pool, phosphonates have been shown to be a dynamic P pool both being assimilated and produced by marine photosynthetic bacteria. The ability of eukaryotic phytoplankton to supplement their growth with phosphonates remains vastly unexplored. Several eukaryotic phytoplankton species have been shown to use glyphosate, a chemically synthesized herbicidal phosphonate, as a P source; it remains unknown if open ocean eukaryotic phytoplankton can utilize phosphonates found naturally in the marine environment. Preliminary experiments suggest at least some eukaryotic phytoplankton are able to directly utilize extracellular phosphonates. This project characterizes the pervasiveness of phosphonate utilization within eukaryotic phytoplankton lineages and identifies the cellular underpinnings that support the acquisition of and growth on naturally occuring phosphonates. The project uses whole-cell transcriptomics and functional gene complementation assays, in addition to phylogenetic analyses, to understand the bioavailability of phosphonates and relevance of phosphonate utilization by natural eukaryotic phytoplankton populations. It is critical to understand the metabolic capabilities of phytoplankton which control marine biogeochemical cycles. This is especially important given the prediction that future oceans may become more stratified which could increase the importance of DOP, including phosphonates, in supporting phytoplankton growth.