Nitrogen fixing organisms - diazotrophs are a key ecological group of the ocean since they provide the food web with biologically fixed ammonium. As the nitrogen fixation requires a high amount of energy, and since the concentration of inorganic phosphorus is subject to fluctuations in the ocean, P may be a limiting inorganic nutrient for this process. Here, we investigated how phosphorus limitation affected the model single-celled diazotrophic cyanobacterial species, Crocosphaera subtropica (formerly Cyanothece) ATCC 51142. We evaluated growth, nitrogen and carbon fixation, photosynthetic efficiency and quantified the energy cost of carbon and nitrogen metabolisms, under P- limited and replete conditions. Overall, growth rates, nitrogen and carbon fixation of C. subtropica decreased under P-limitation. Interestingly, nitrogen fixation showed a shift towards the latest hours of the dark period compared to the early peak displayed by the P- replete culture. Moreover, P usage efficiency for nitrogen and carbon fixation were, respectively, three- and two-times lower in the P- limited than in the replete condition. Despite the reduction in growth rates and nitrogen and carbon fixation, our data suggest that C. subtropica is still able to grow under P- limiting condition. While improving our understanding of P limitation in relation to the physiological process of nitrogen fixation, the results help to model nitrogen fixation on a global scale.

Primary Presenter: Saverio Rana, Mikrobiologický ústav AV ČR, v. v. i. (rana@alga.cz)

Authors:

Saverio Rana,  Institute of Microbiology, Centre Algatech, Czech Academy of Sciences, Trebon, Czech Republic  (rana@alga.cz)

Eva Kotabova, Institute of Microbiology, Centre Algatech, Czech Academy of Sciences, Trebon, Czech Republic  ()

Martin Lukes,  Institute of Microbiology, Centre Algatech, Czech Academy of Sciences, Trebon, Czech Republic  ()

Marie Vacova, Faculty of Sciences, University of South Bohemia, Ceske Budejovice, Czech Republic  ()

Ondrej Prasil, Institute of Microbiology, Centre Algatech, Czech Academy of Sciences, Trebon, Czech Republic  (prasil@alga.cz)