Collaborative Research: Antarctic Diatom Proteorhodopsins: Characterization and a Potential Role in the Iron-limitation Response

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Proteorhodopsins are proteins that are embedded in membranes that can act as light-driven proton pumps to generate energy for metabolism and growth. The discovery of proteorhodopsins in many diverse marine prokaryotic microbes has initiated extensive investigation into their distributions and functional roles. Recently, a proton-pumping, rhodopsin-like gene was identified in diatoms, a group of marine phytoplankton that dominates the base of the food web in much of the Southern Ocean. Since this time, proteorhodopsins have been identified in many, but not all, diatom species. The proteorhodopsin gene is more frequently found in diatoms residing in cold, iron-limited regions of the ocean, including the Southern Ocean, than in diatoms from other regions. It is thought that proteorhodopsin is especially suited for use energy production in the Southern Ocean since it uses no iron and its reaction rate is insensitive to temperature (unlike conventional photosynthesis). The overall objective of the project is to characterize Antarctic diatom-proteorhodopsin and determine its role in the adaptation of these diatoms to low iron concentrations and extremely low temperatures found in Antarctic waters. This research will provide new information on the genetic underpinnings that contribute to the success of diatoms in the Southern Ocean and how this unique molecule may play a pivotal role in providing energy to the base of the Antarctic food web. Broader impact activities are aimed to promote the teaching and learning of polar marine-sciences related topics by translating research objectives into readily accessible educational materials for middle-school students.This project will combine molecular, biochemical and physiological measurements to determine the role and importance of proteorhodopsin in diatom isolates from the Western Antarctic Peninsula region. Proton-pumping characteristics and pumping rates of proteorhodopsin as a function of light intensity and temperature, the resultant proteorhodopsin-linked intracellular ATP production rates, and the cellular localization of the protein will be determined. The project will examine the environmental conditions where Antarctic diatom-proteorhodopsin is most highly expressed and construct a cellular energy budget that includes diatom-proteorhodopsin when grown under these different environmental conditions. Estimates of the energy flux generated by proteorhodopsin will be compared to total energy generation by the photosynthetic light reactions and metabolically coupled respiration rates. Finally, the characteristics and gene expression of diatom-proteorhodopsin in Antarctic diatoms and a proteorhodopsin-containing diatom isolates from temperate regions will be compared in order to determine if there is a preferential dependence on energy production through proteorhodopsin in diatoms residing in cold, iron-limited regions of the ocean. Educational activities will be performed in collaboration with the Morehead Planetarium and Science Center who co-ordinates the SciVentures program, a popular summer camp for middle-school students from Chapel Hill and surrounding areas. In collaboration with the Planetarium, the researchers will develop activities that focus on phytoplankton and the important role they play within polar marine food webs for the SciVentures participants. Additionally, a teaching module on Antarctic phytoplankton will be developed for classrooms and made available to educational networking websites and presented at workshops for science educators nationwide.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.