Flux capacities and acclimation costs in Trichodesmium from the Gulf of Mexico
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Phytoplankton function and acclimation are driven by catalytic protein complexes that mediate key physiological transformations, including generation of photosynthetic ATP and reductant, and carbon and nitrogen fixation. Quantitation of capacities for these processes allows estimation of rates for key ecosystem processes, and identification of factors limiting primary productivity. We herein present molar quantitations of PSI, PSII, ATP synthase, RuBisCO and the Fe protein of nitrogenase of Trichodesmium collected from the Gulf of Mexico, in comparison to determinations for a range of cyanobacteria growing in culture. Using these measurements, estimates were generated for Trichodesmium capacities for carbon fixation of 1–3.4 g C g chl a −1 h−1 and nitrogen fixation of 0.06–0.17 g N g chl a −1 h−1, with diel variations in capacities. ATP synthase levels show that ATP synthesis capacity is sufficient to support these levels of carbon and nitrogen fixation, and that ATP synthase levels change over the day in accordance with the ATP demands of nitrogenase and RuBisCO activity. Levels of measured complexes indicate that Trichodesmium manifests n-type diel light acclimation through rapid changes in RuBisCO:PSII, supported by significant investment of cellular nitrogen. The plasticity in the levels and stoichiometry of these core complexes show that changes in the abundance of core protein complexes are an important component of acclimation and regulation of metabolic function by Trichodesmium populations.
KeywordsRbcL Diel Cycle MoFe Protein RuBisCO Content Diazotrophic Cyanobacterium
This work was supported by an NSERC Discovery grant and funding from the Canada Research Chair and Canadian Foundation for Innovation to DAC. CMB was the recipient of an NSERC Industrial Postgraduate Scholarship in collaboration with AgriSera AB. AMC was partially supported by the RTI Program of the New Brunswick Innovation Foundation. AgriSera AB (http://www.agrisera.se) and Environmental Proteomics NB (http://www.environmentalproteomics.ca) collaborated on the production of immunodetection reagents. We thank Drs. Yannick Huot, Zoe Finkel, Andrew Irwin, Christophe Six and Joanna Porankiewicz-Asplund for discussions. Contribution number 1454 from The University of Texas Marine Science Institute. The research described complies with the current laws of Canada and the United States of America.
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