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

Project description from NSF award 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.

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.