title: Marine diatom proteorhodopsins and their potential role in coping with low iron availability.
abstract: Proteorhodopsins (PR) are retinal-binding membrane proteins that function as light-driven proton pumps to generate energy for metabolism and growth. Recently PR-like genes have been identified in some marine eukaryotic protists, including diatoms, dinoflagellates, haptophytes and cryptophytes. These rhodopsins are homologous to green-light-absorbing, ATP-generating PRs present within bacteria. Here we show that in the oceanic diatom Pseudo-nitzschia granii, PR-like gene and protein expressions increase appreciably under iron limitation. In a survey of available transcriptomes, PR-like genes in diatoms are generally found in isolates from marine habitats where seasonal to chronic growth limitation by the micronutrient iron is prevalent, yet similar biogeographical patterns are not apparent in other phytoplankton taxa. We propose that rhodopsin-based phototrophy could account for a proportion of energy synthesis in marine eukaryotic photoautotrophs, especially when photosynthesis is compromised by low iron availability. This alternative ATP-generating pathway could have significant effects on plankton community structure and global ocean carbon cycling.
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Adrian
authors.initials: A
authors.lastname: Marchetti
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Dylan
authors.initials: D
authors.lastname: Catlett
authors.affiliation: Department of Marine Sciences, University of Georgia, Athens, GA, USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hopkinson
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Kelsey
authors.initials: K
authors.lastname: Ellis
authors.affiliation: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Cassar
mesh_terms: D017377:Diatoms / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D007501:Iron / Q000378:metabolism*; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009792:Oceans and Seas; D010788:Photosynthesis; D010839:Phytoplankton / Q000235:genetics / Q000378:metabolism; D025604:Rhodopsins, Microbial / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D008565:Membrane Proteins; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D007501:Iron