Marine Oscillatoria ( Trichodesmium ): Explanation for Aerobic Nitrogen Fixation Without Heterocysts

Authors:
  • ECEdward J. Carpenter
    Edward J. Carpenter
  • CPCharles C. Price
    Charles C. Price
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Abstract
Nitrogen fixation in marine Oscillatoria appears to be associated with differentiated cells located in the center of the colony. These central cells exhibit reduced pigmentation relative to peripherally located cells and do not incorporate 14 CO 2 in photosynthesis. Central cells apparently do not produce O 2 which would deactivate nitrogenase. When central cells are exposed to O 2 via disruption of the colonies, N 2 fixation (acetylene reduction) decreases sharply even though individual trichomes remain intact. Disruption of colonies in the absence of O 2 does not cause reduced nitrogenase activity. In the sea, turbulence from wave action apparently separates trichomes allowing O 2 to enter thus decreasing nitrogenase activity. These observations explain how Oscillatoria is able to fix N 2 without heterocysts in an aerobic environment and why its blooms virtually always occur in calm seas.

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