The Role of Bacterial Symbionts of Marine Sponges in Nitrogen Fixation

海洋海绵是复杂微生物群落的宿主，这些微生物群落可能占海绵生物量的60%。人们对这些共生细菌的作用和它们对海绵的贡献知之甚少，从而间接地对海绵生活的珊瑚礁生态系统作出了贡献。推动该项目的假设是，固氮细菌的不同组合在为海绵提供氮、吸收氮气并将其转化为海绵可以使用的有机氮方面发挥着重要作用。研究了来自美国佛罗里达州Key Largo的两种海绵细菌共生体——绿僵菌（Ircinia strobilina）和mycallelaxissima在固氮中的作用。该项目将包括生物化学方法来证明整个海绵和细菌分离物的固氮作用，以及分子方法来研究nifH基因在何时何地被激活并产生nifH蛋白的模式，nifH蛋白是固氮作用的关键蛋白。为研究生提供海洋微生物学培训，鼓励少数民族本科生参加暑期海洋微生物学课程，从事科研工作。该项目将促进我们对复杂海绵共生中微生物多样性和功能的理解，促进海绵共生作为微生物与许多高等生物之间复杂共生关系的模型的研究。该项目将为脆弱的珊瑚礁环境提供有关氮源的新信息。

Marine sponges are hosts to complex microbial communities that may comprise up to 60% of the sponge biomass. Little is known about the roles of these symbiotic bacteria and their contributions to the sponge and thereby indirectly to the coral reef ecosystem in which the sponges live. The hypothesis driving the project is that diverse assemblages of nitrogen-fixing bacteria play an important role in providing sponges with nitrogen, taking nitrogen gas and converting it to organic forms of nitrogen that can be used by sponges. The role of bacterial symbionts of two sponges from Key Largo, Florida, Ircinia strobilina and Mycale laxissima in nitrogen fixation will be determined. The project will include biochemical approaches to demonstrate nitrogen fixation in whole sponges and bacterial isolates, and molecular approaches to study the pattern of where and when the nifH gene is turned on and makes the NifH protein, a key protein in nitrogen fixation. Training will be provided in marine microbiology to graduate students and undergraduate minority students will be encouraged to enter careers in scientific research by participating in a summer course in Marine Microbiology. The project will advance our understanding of microbial diversity and function in complex sponge symbioses, promoting the study of sponge symbioses as models of the complex symbiotic relationships found between microbes and many higher organisms. The project will provide new information on sources of nitrogen for fragile coral reef environments.