EAGER: Investigate a novel way of light harvesting by marine phytoplankton: proton-pump rhodopsin in dinoflagellates

University Of Connecticut, Storrs CT

Investigators

Abstract

Photosynthesis was the only known pathway of phototrophy in marine ecosystems until the early 2000s, when a proton-pump type of rhodopsin (proteorhodopsin, or PR) was found to occur in marine bacteria living in the sunlit ocean surface, and its role in facilitating trans-membrane proton transport that leads to ATP production was demonstrated. It has since been found that the PR gene occurs in 13% to 80% of marine bacteria and archaea in the ocean's surface waters. The PIs recently detected a rhodopsin gene in marine dinoflagellates that is closely related to the proton-pump type, but direct evidence of its proton-pump action in this group of organisms is lacking. Given the importance of dinoflagellates as oceanic primary producers and micrograzers, it should be determined if rhodopsin-based phototrophy plays an important role in sustaining dinoflagellate growth, enabling dinoflagellates to outcompete other groups of phytoplankton in nutrient-limited environments. Intellectual Merit: This study will address two central questions: 1) Does the gene discovered in dinoflagellates indeed code for a rhodopsin that absorbs light and leads to the production of ATP? and 2) How common is this gene in dinoflagellate communities? These questions need to be addressed before moving on to the question of how much dinoflagellate rhodopsin contributes to overall energy acquisition in the marine ecosystem. The current study will: (1) transform the dinoflagellate rhodopsin gene into E. coli cells to test for light-induced ATP-generation under controlled laboratory conditions; (2) analyze representative dinoflagellates (cultured and wild) from Long Island Sound for presence of the gene; and (3) examine the diversity of dinoflagellate rhodopsin sequences under contrasting temperature (seasons) and nutrient (spatial) conditions in Long Island Sound. Due to the risk (of no proton pumping function) and limited background work, this proposal would not likely succeed if submitted as a full-fledged project. The EAGER program provides a mechanism for exploring these risky but potentially important questions. Broader Impacts: This study will provide essential information for understanding how much eukaryotic rhodopsin may contribute to marine phototrophy. The results will provide a basis on which to determine whether major research efforts should be invested in the future to systematically investigate the ecological significance of this gene in marine ecosystems. This project will also contribute to education and training. First, a graduate class (Molecular Approaches to Biological Oceanography) will be involved in part of the project as a required research component of the course. Second, the project will provide training opportunities to one or two undergraduate students in marine science research in general and molecular ecology of plankton in particular.