title: In Synechococcus sp. competition for energy between assimilation and acquisition of C and those of N only occurs when growth is light limited.
abstract: The carbon-concentrating mechanisms (CCMs) of cyanobacteria counteract the low CO2 affinity and CO2:O2 selectivities of the Rubisco of these photolithotrophs and the relatively low oceanic CO2 availability. CCMs have a significant energy cost; if light is limiting, the use of N sources whose assimilation demands less energy could permit a greater investment of energy into CCMs and inorganic C (Ci) assimilation. To test this, we cultured Synechococcus sp. UTEX LB 2380 under either N or energy limitation, in the presence of NO3- or NH4+. When growth was energy-limited, NH4+-grown cells had a 1.2-fold higher growth rate, 1.3-fold higher dissolved inorganic carbon (DIC)-saturated photosynthetic rate, 19% higher linear electron transfer, 80% higher photosynthetic 1/K1/2(DIC), 2.0-fold greater slope of the linear part of the photosynthesis versus DIC curve, 3.5-fold larger intracellular Ci pool, and 2.3-fold higher Zn quota than NO3--grown cells. When energy was not limiting growth, there were not differences between NH4+- and NO3--grown cells, except for higher linear electron transfer and larger intracellular Ci pool.We conclude that, when energy limits growth, cells that use the cheaper N source divert energy from N assimilation to C acquisition and assimilation; this does not happen when energy is not limiting.
authors.affiliation: Marine Biology Institute, Science Center, Shantou University, Shantou, Guangdong 515063, China.|Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Ancona 60131, Italy.
authors.forename: Zuoxi
authors.initials: Z
authors.lastname: Ruan
authors.affiliation: Division of Plant Sciences, University of Dundee at the James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK.|Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Ultimo NSW 2007, Australia.
authors.forename: John A
authors.initials: JA
authors.lastname: Raven
authors.affiliation: Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Ancona 60131, Italy.|Institute of Microbiology ASCR, Algatech, Trebon, Czech Republic.|National Research Council, Institute of Marine Science, Venezia, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Giordano
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D004734:Energy Metabolism; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis; D046940:Synechococcus / Q000378:metabolism*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D002245:Carbon Dioxide; D009584:Nitrogen
keywords: Ammonium; CO2 concentrating mechanisms (CCMs); cyanobacteria; internal carbon pool; nitrate