title: Combined effects of CO2 and light on the N2-fixing cyanobacterium Trichodesmium IMS101: a mechanistic view.
abstract: The marine diazotrophic cyanobacterium Trichodesmium responds to elevated atmospheric CO(2) partial pressure (pCO(2)) with higher N(2) fixation and growth rates. To unveil the underlying mechanisms, we examined the combined influence of pCO(2) (150 and 900 microatm) and light (50 and 200 micromol photons m(-2) s(-1)) on Trichodesmium IMS101. We expand on a complementary study that demonstrated that while elevated pCO(2) enhanced N(2) fixation and growth, oxygen evolution and carbon fixation increased mainly as a response to high light. Here, we investigated changes in the photosynthetic fluorescence parameters of photosystem II, in ratios of the photosynthetic units (photosystem I:photosystem II), and in the pool sizes of key proteins involved in the fixation of carbon and nitrogen as well as their subsequent assimilation. We show that the combined elevation in pCO(2) and light controlled the operation of the CO(2)-concentrating mechanism and enhanced protein activity without increasing their pool size. Moreover, elevated pCO(2) and high light decreased the amounts of several key proteins (NifH, PsbA, and PsaC), while amounts of AtpB and RbcL did not significantly change. Reduced investment in protein biosynthesis, without notably changing photosynthetic fluxes, could free up energy that can be reallocated to increase N(2) fixation and growth at elevated pCO(2) and light. We suggest that changes in the redox state of the photosynthetic electron transport chain and posttranslational regulation of key proteins mediate the high flexibility in resources and energy allocation in Trichodesmium. This strategy should enable Trichodesmium to flourish in future surface oceans characterized by elevated pCO(2), higher temperatures, and high light.
authors.affiliation: The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat-Gan, Israel. levitao@mail.biu.ac.il
authors.forename: Orly
authors.initials: O
authors.lastname: Levitan
authors.forename: Sven A
authors.initials: SA
authors.lastname: Kranz
authors.forename: Dina
authors.initials: D
authors.lastname: Spungin
authors.forename: Ondrej
authors.initials: O
authors.lastname: Prásil
authors.forename: Björn
authors.initials: B
authors.lastname: Rost
authors.forename: Ilana
authors.initials: I
authors.lastname: Berman-Frank
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects; D001426:Bacterial Proteins / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects* / Q000201:enzymology / Q000528:radiation effects*; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D004734:Energy Metabolism / Q000187:drug effects; D005453:Fluorescence; D008027:Light; D055595:Mechanical Phenomena / Q000187:drug effects / Q000528:radiation effects; D009586:Nitrogen Fixation / Q000187:drug effects* / Q000528:radiation effects*; D009591:Nitrogenase / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D021122:Protein Subunits / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D002734:Chlorophyll; D002245:Carbon Dioxide; D009591:Nitrogenase