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N2 fixation by the colony-forming cyanobacterium Trichodesmium is an important source of new nitrogen in the North Pacific Subtropical Gyre. For understanding the ecology and physiology of this keystone species in a changing climate, we need to consider the implications of colony formation for chemical microenvironments and biotic interactions. In this study, we characterized gradients of O2 and pH as well as single-cell fluxes of C and N under different pCO2 levels in Trichodesmium colonies collected at Station ALOHA. Microsensor measurements indicated that cells within colonies experienced large fluctuations in O2, pH and CO2 concentrations over a day-night cycle. Yet, colonies exposed to light were supersaturated with O2 throughout the light period and anoxia was not detected. Alternating between light and dark conditions caused a variation in pH levels by on average 0.5 units. Single-cell analyses of C and N uptake using secondary ion mass spectrometry (nanoSIMS) revealed high variability in the metabolic activity of single cells and trichomes of Trichodesmium, and indicated transfer of C and N to colony-associated non-photosynthetic bacteria. Neither O2 fluxes nor C fixation were significantly influenced by short-term incubations under different pCO2 levels, whereas N2 fixation increased with increasing pCO2. The large range of metabolic rates observed at the single-cell level may reflect a response by colony-forming microbial populations to highly variable microenvironments.


Eichner, M., University of Gothenburg, Sweden,

Klawonn, I., Leibnitz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany,

Wilson, S. T., Center for Microbial Oceanography: Research and Education (C-MORE), USA,

Littmann, S., Max Planck Institute for Marine Microbiology, Germany,

Whitehouse, M., Natural History Museum Stockholm, Sweden,

Church, M. J., Center for Microbial Oceanography: Research and Education (C-MORE), USA,

Kuypers, M. M., Max Planck Institute for Marine Microbiology, Germany,

Karl, D. M., Center for Microbial Oceanography: Research and Education (C-MORE), USA, 'David Karl'

Ploug, H., University of Gothenburg, Sweden,


Oral presentation

Session #:040
Date: 03/01/2017
Time: 12:15
Location: 314

Presentation is given by student: No