title: Energy cost and putative benefits of cellular mechanisms modulating buoyancy in aflagellate marine phytoplankton.
abstract: Little information is available on the energetics of buoyancy modulation in aflagellate phytoplankton, which comprises the majority of autotrophic cells found in the ocean. Here, we computed for three aflagellate species of marine phytoplankton (Emiliania huxleyi, Thalassiosira pseudonana, and Ethmodiscus rex) the theoretical minimum energy cost as photons absorbed and nitrogen resource required of the key physiological mechanisms (i.e., replacement of quaternary ammonium by dimethyl-sulfoniopropionate, storage of polysaccharides, and cell wall biosynthesis) affecting the cell's vertical movement as a function of nitrogen (N) availability. These energy costs were also normalized to the capacity of each buoyancy mechanism to modulate sinking or rising rates based on Stokes' law. The three physiological mechanisms could act as ballast in the three species tested in conditions of low N availability at a low fraction (<12%) of the total photon energy cost for growth. Cell wall formation in E. huxleyi was the least costly ballast strategy, whereas in T. pseudonana, the photon energy cost of the three ballast strategies was similar. In E. rex, carbohydrate storage and mobilization appear to be energetically cheaper than modulations in organic solute synthesis to achieve vertical migration. This supports the carbohydrate-ballast strategy for vertical migration for this species, but argues against the theory of replacement of low- or high-density organic solutes. This study brings new insights into the energy cost and potential selective advantages of several strategies modulating the buoyancy of aflagellate marine phytoplankton.
authors.affiliation: Québec-Océan and Unité Mixte Internationale Takuvik Ulaval-CNRS, Département de Biologie, Université Laval, Québec, Québec, Canada, G1V 0A6.
authors.forename: Michel
authors.initials: M
authors.lastname: Lavoie
authors.affiliation: Division of Plant Science, University of Dundee at the James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK.|Functional Plant Biology and Climate Change Cluster (C3), University of Technology Sydney, Ultimo, NSW, 2007, Australia.
authors.forename: John A
authors.initials: JA
authors.lastname: Raven
authors.affiliation: Québec-Océan and Unité Mixte Internationale Takuvik Ulaval-CNRS, Département de Biologie, Université Laval, Québec, Québec, Canada, G1V 0A6.
authors.forename: Maurice
authors.initials: M
authors.lastname: Levasseur
mesh_terms: D059001:Aquatic Organisms / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D002241:Carbohydrates / Q000494:pharmacology; D002244:Carbon / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D005407:Flagella; D007477:Ions; D008903:Minerals / Q000378:metabolism; D009068:Movement; D009584:Nitrogen / Q000172:deficiency; D010839:Phytoplankton / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D012822:Silicon Dioxide / Q000494:pharmacology; D013452:Sulfonium Compounds / Q000494:pharmacology
chemical_list: D002241:Carbohydrates; D007477:Ions; D008903:Minerals; D013452:Sulfonium Compounds; D002244:Carbon; D012822:Silicon Dioxide; C068078:dimethylpropiothetin; D009584:Nitrogen
keywords: carbohydrates; coccoliths; dimethylsulfoniopropionate; glycine betaine; nitrogen; silica mineralization