Nitrogen metabolism in phytoplankton under natural conditions and the presence of inorganic fertiliser and organic waste

自然条件下以及无机肥料和有机废物存在下浮游植物的氮代谢

• 批准号: 2505809
• 金额: --
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2505809
• 关键词: Nitrogen; metabolism; phytoplankton; under; natural

Nitrogen is an essential nutrient controlling phytoplankton productivity in freshwater ecosystems. In aquatic environments, some bacteria can transform atmospheric nitrogen gas (N2) into bioavailable forms (ammonium, nitrates). The dissolved N pool is dominated by dissolved organic N compounds (80-90%), with around 10-20% in the form of inorganic N compounds, both organic and inorganic N compounds can be easily assimilated into living systems. Worldwide, the increasing export of N to waters from the use of artificial fertilisers (Haber-Bosch), livestock production and the discharge of N rich effluent from wastewater treatment works together with atmospheric N deposition, have contributed to nutrient pollution of freshwater ecosystems with adverse consequences for ecosystem health. These have likely affected the species assemblages, distribution and productivity of the phytoplankton community, though our understanding of these impacts is incomplete, particularly in freshwater ecosystems. Picophytoplankton play a key role in global primary productivity, particularly in natural freshwaters. Ecological studies have previously suggested that both marine and freshwater picocyanobacteria represent the main component of picophytoplankton in low nutrient habitats exceeding the eukaryotic component. Despite their central role in the food chain dynamics (e.g. as a food source for flagellates and larger grazers), freshwater picocyanobacteria remain poorly studied, especially at the genomic level and in comparison, to their closest relatives in marine habitats. Furthermore, traditional cell count methodologies and molecular ecology studies have identified picocyanobacteria seasonal changes in terms of abundance in freshwater lakes, yet few studies have studied seasonal changes in phytoplankton communities, and/or in relation to the changing chemistry of the dissolved N pool as this varies along gradients of nutrient enrichment. A handful of freshwater picocyanobacteria genomes studies have identified genes involved in nitrate incorporation as well as chitin degradation (a polymer produced by fungi and arthropods). The latter suggests that complex organic molecules might be bioavailable, supporting evidence emerging from recent laboratory bioassay research led by the supervisors. However, the metabolic pathway, genetic information and biochemical mechanisms used by the freshwater picophytoplankton in assimilating environmental sources of nitrogen are not well understood. Using an interdisciplinary approach this project aims to study how picocyanobacteria communities respond to different gradients and chemical forms of nitrogen availability both in the field and under controlled lab experiments. The student will design and carry out novel experiments to isolate, culture, and sequence picocyanobacteria from the English Lake District, where long-term contextual data are available and the nearby Cotswold Water Park at South Cerney. The questions this studentship will address are as follows: 1. How do picocyanobacteria communities change across different trophic/nutrient gradients, and in relation to other microorganisms? 2. What is the nitrogen assimilation machinery present in picocyanobacteria? How are these genes expressed under different experimental conditions? 3. How does the presence of artificial fertilisers and organic waste affect N assimilation by picocyanobacteria under controlled lab conditions?

氮是淡水生态系统中控制浮游植物生产力的重要营养元素。在水生环境中，一些细菌可以将大气中的氮气（N2）转化为生物可利用的形式（铵，硝酸盐）。溶解态氮库主要是溶解态有机氮化合物（80-90%），约10-20%以无机氮化合物的形式存在，有机和无机氮化合物都很容易被生物系统吸收。在世界范围内，越来越多的氮输出到沃茨从使用人工肥料（哈伯-博世），畜牧业生产和排放的富氮污水从废水处理工程与大气中的氮沉降，造成营养污染的淡水生态系统的生态系统健康的不利后果。这些可能影响了浮游植物群落的物种组合、分布和生产力，尽管我们对这些影响的了解还不完全，特别是在淡水生态系统中。浮游藻类在全球初级生产力中起着关键作用，特别是在天然淡水中。生态研究表明，海洋和淡水picocyanobacteria代表picophytoplankton的主要组成部分，在低营养的栖息地超过了真核生物的组成部分。尽管它们在食物链动态中发挥着核心作用（例如作为鞭毛虫和大型食草动物的食物来源），但淡水微蓝细菌的研究仍然很少，特别是在基因组水平上，与海洋栖息地中最接近的亲属相比。此外，传统的细胞计数方法和分子生态学研究已经确定了picocyanobacteria的季节性变化在淡水湖泊中的丰度方面，但很少有研究浮游植物群落的季节性变化，和/或有关的溶解氮池的化学变化，因为这沿着梯度的营养富集。一些淡水微蓝细菌基因组研究已经确定了参与硝酸盐掺入以及几丁质降解（真菌和节肢动物产生的聚合物）的基因。后者表明，复杂的有机分子可能是生物可利用的，这支持了最近由主管领导的实验室生物测定研究中出现的证据。然而，淡水微型浮游植物吸收环境氮源的代谢途径、遗传信息和生化机制尚不清楚。使用跨学科的方法，该项目旨在研究微蓝细菌群落如何在田间和受控实验室实验中对不同梯度和化学形式的氮可用性做出反应。学生将设计和进行新的实验，以分离，培养和测序picocyanobacteria从英国湖区，在那里可以获得长期的上下文数据和附近的科茨沃尔德水上公园在南Cerney。这个学生奖学金将解决的问题如下：1。微蓝细菌群落如何在不同营养/营养梯度中变化，以及与其他微生物的关系？2.微蓝细菌的氮同化机制是什么？这些基因在不同的实验条件下如何表达？3.在受控的实验室条件下，人工肥料和有机废物的存在如何影响微蓝细菌的氮同化作用？