title: The use of NH4+rather than NO3-affects cell stoichiometry, C allocation, photosynthesis and growth in the cyanobacterium Synechococcus sp. UTEX LB 2380, only when energy is limiting.
abstract: The assimilation of N-NO3-requires more energy than that of N-NH4+. This becomes relevant when energy is limiting and may impinge differently on cell energy budget depending on depth, time of the day and season. We hypothesize that N-limited and energy-limited cells of the oceanic cyanobacterium Synechococcus sp. differ in their response to the N source with respect to growth, elemental stoichiometry and carbon allocation. Under N limitation, cells retained almost absolute homeostasis of elemental and organic composition, and the use of NH4+did not stimulate growth. When energy was limiting, however, Synechococcus grew faster in NH4+than in NO3-and had higher C (20%), N (38%) and S (30%) cell quotas. Furthermore, more C was allocated to protein, whereas the carbohydrate and lipid pool size did not change appreciably. Energy limitation also led to a higher photosynthetic rate relative to N limitation. We interpret these results as an indication that, under energy limitation, the use of the least expensive N source allowed a spillover of the energy saved from N assimilation to the assimilation of other nutrients. The change in elemental stoichiometry influenced C allocation, inducing an increase in cell protein, which resulted in a stimulation of photosynthesis and growth.
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: 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: D000255:Adenosine Triphosphate / Q000378:metabolism; D064751:Ammonium Compounds / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D018533:Biomass; D002241:Carbohydrates / Q000032:analysis; D002244:Carbon / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects; D008055:Lipids / Q000032:analysis; D009566:Nitrates / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D013455:Sulfur / Q000378:metabolism; D046940:Synechococcus / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism
chemical_list: D064751:Ammonium Compounds; D001426:Bacterial Proteins; D002241:Carbohydrates; D008055:Lipids; D009566:Nitrates; D010758:Phosphorus; D013455:Sulfur; D002244:Carbon; D000255:Adenosine Triphosphate; D009584:Nitrogen; D010100:Oxygen
keywords: FTIR; carbon allocation; cyanobacteria; elemental stoichiometry; energy; nitrogen