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.
The project investigated the interaction of a harmful bloom forming algal species, Pseudo-nitzschia, and its microbiome (associated bacteria). The results showed that the growth and toxin production of the algae are significantly influenced by the microbiome. Each species has its own group of microbiome. Native microbiome supports the fitness of the host algal species and the presence of foreign bacteria may deter the growth of alga and increase the production of algal toxin, domoic acid. The research also showed the interaction of bacteria and algae can be achieved through communication through small chemical molecules that diffuse outside the cell membrane, called quorum sensing. Algae attract their microbiome by excretion of organic algal exudates that can be utilized by specific bacteria. The discovery of the host-specificity of microbiome features as well as the characterization of microbiome members based on genetic relation and function shed light not only on the fundamental of microbial ecology in the aquatic environment but also provide insight to co-evolution of algae-microbiome associations, microbiome population dynamics, and survival strategies utilized by aquatic microbiome members. In addition to the contributions to the scientific field, the results of this study could potentially be utilized to develop improved harmful algal bloom management tools. Two female postdoctoral researchers were trained in this project. One of them has successfully moved onto a tenure track faculty position. The project also offered research opportunity to five undergraduate students. The results of the research were incorporated into general education materials in the public outreach program to teach the community about the natural of harmful algal blooms.
