Interactions of bacteria, viruses and bloom-forming diatom genus Pseudo-nitzschia

知识价值：这个项目试图阐明病毒、细菌和沿海海洋环境中有毒的形成水华的海洋硅藻属伪菱形藻之间的相互作用。世界范围内的拟菱形藻(Passo-nitschia sp.)(芽孢杆菌)在世界各地造成有害的藻类水华。最近两个海洋硅藻的基因组序列显示，细菌基因占它们基因组组成的5%，这突显了海洋硅藻在进化史上与细菌的密切联系。到目前为止，很少有人研究硅藻与其共生细菌的相互作用，也没有人用直接的实验方法研究病毒、细菌和浮游植物的相互作用。本项目研究藻类-微生物群落的生理、生化、遗传和生态相互作用，以破译微生物对藻类水华动态和毒素产生的影响。本研究综合了系统发育学、生理学、生物化学、比较基因组学和元基因组学的方法，寻求以下问题的答案：1)与不同种类的拟菱形藻相关的附生细菌是什么，它们在水华的不同阶段是如何变化的？2)这些细菌如何影响拟菱形藻宿主的生理，藻类宿主如何调节这些微生物的相互作用？3)病毒能否通过选择性地溶解溶藻细菌来促进水华的发生，同时为促进生长的细菌创造机会，或者反之亦然？该项目是在微生物-藻类相互作用的初步研究的指导下进行的，在这些研究中，发现两个假菱形藻存在显著不同的共生细菌群落。一株拟菱形藻的细菌伴生菌刺激了藻类宿主的生长，但对另一种拟菱形藻起病原菌的作用。该项目将通过对更多种类的伪菱形藻进行采样，并调查沿海海域伪菱形藻水华开始、高峰和衰退期后共生和浮游细菌群落结构的变化，扩大关于共生细菌群落多样性和动态的工作。藻类寄主对表生细菌联合的响应将采用双培养和多培养的生理实验方法进行研究。藻类宿主和表生细菌之间的化学交流将通过使用已建立的LC-MS和酶分析方法观察藻类渗出物和细菌酶分泌物来解决。为了阐明病毒对细菌-藻类相互作用的影响，将分离出针对共生细菌的噬菌体，并将其纳入生理实验。广泛影响：该项目将环境科学和工程方面的教育与深入研究藻类水华期间的微生物相互作用结合在一起。将通过培训一名少数族裔博士后研究员、扩大环境科学中代表性不足的群体的参与、让本科生及早接触环境研究以及接触社会来实现这一整合。研究中少数族裔参与者的招募和培训将与少数群体科学计划(MSP)和加州少数群体参与联盟(CAMP)计划合作进行。与暑期本科生研究计划(SURP)一起，本科生将在UCI学习的早期阶段被招募参加这个项目。将与加州鱼类和猎物部管理的纽波特后湾科学中心合作，向社会和7-12年级的学生伸出援手。

Intellectual Merit: This project seeks to elucidate the interactions between viruses, bacteria and toxic bloom-forming marine diatom genus Pseudo-nitzschia in the coastal marine environment. The cosmopolitan Pseudo-nitzschia sp. (Bacillariophyceae) causes harmful algal blooms in various parts of the world. Recent genome sequences of two marine diatoms revealed that bacterial genes contribute up to 5% of their genome make-up, highlighting the close association of marine diatoms with bacteria in evolutionary history. So far, few have looked at the interactions of diatoms with their epibiotic bacteria and none have studied the interactions of virus, bacteria and phytoplankton using direct experimental approach. This project investigates the physiological, biochemical, genetic and ecological interactions of algae-microbe associations in order to decipher the influences of microbes on algal bloom dynamics and toxigenesis. By incorporating methods in phylogeny, physiology, biochemistry, comparative genomics and metagenomics, the research seeks answers to the following questions: 1) What are the epiphytic bacteria associating with different species of Pseudo-nitzschia and how do they change at different stages of the bloom? 2) How do these bacteria affect the physiology of the Pseudo- nitzschia hosts and how does the algal host regulate these microbial interactions? 3) Can viruses promote a bloom by selectively lysing algicidal bacteria, while creating opportunities for growth- promoting bacteria or vice versa? This project is guided by the preliminary research on microbe- algae interaction, where significantly different epibiotic bacterial communities were found to associate with two Pseudo-nitzschia species. Bacterial associates of one Pseudo-nitzschia sp. stimulated the growth of the algal-host but acted as a pathogen on another Pseudo-nitzschia sp. This project will expand the work on epibiotic bacterial community diversity and dynamics by sampling additional species of Pseudo-nitzschia and investigating the changes in epibiotic and planktonic bacterial community structure following the initiation, peak and decline phases of Pseudo-nitzschia blooms in coastal oceans. Algal host responses to epibionts association will be investigated using physiological experiments of binary and multi-culture experimental approaches. The chemical communication between algal host and epibiont bacteria will be addressed by looking at the algal exudate excretions and bacterial enzyme secretions using established LC-MS and enzyme assays. To illustrate the influences of viruses on bacterial-algal interaction, bacteriophages specific to epibiotic bacteria will be isolated and included in the physiological experiments.Broader Impacts: This project integrates education in environmental science and engineering with in-depth investigation of microbial interactions during algal bloom. The integration will be achieved through training of a minority postdoctoral fellow, broadening the participation of underrepresented groups in environmental science, early exposure of undergraduate students to environmental research, and outreach to society. The recruitment and training of minority participants in the research will be conducted in collaboration with Minority Science Program (MSP) and the California Alliance for Minority Participation (CAMP) program. Jointly with Summer Undergraduate Research Program (SURP), undergraduate students will be recruited to participate in this project at the early stage of their study in UCI. Outreach to society and 7th-12th grades students will be accomplished in collaboration with the Newport Back Bay Science Center managed by the California Department of Fish and Game.