Studies on nitrogen fixation and photosynthesis in blue-green algae

• Main Author: Tozum, S. R. D.
• Published: Swansea University 1980
• Subjects: 579.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639257

The relationships between photosynthesis and acetylene reduction (nitrogen fixation) have been examined, mainly in the unicellular blue-green alga Gloeocapsa, though for comparative purposes, a second unicellular alga, Aphanothece pellida, and the filamentous heterocystous alga, Anabaena cylindrica, have also been studied. Glococapsa can fix nitrogen in the dark, so there is no obligatory link between photosynthesis and nitrogen fixation in this organism. However, studies using inhibitors of photosynthesis suggest that, in the light, electrons derived photosynthetically from water can be used, directly for nitrogen fixation by Gloeocapsa. This suggestion is supported by the action spectra and Emerson enhancements of photosynthesis and nitrogen fixation. Photosynthesis apparently also supplies ATP for nitrogen fixation in the light, though in the dark both oxidative and substrate-level phosphorylation can support nitrogen fixation. Finally, possible mechanisms by which the oxygen-sensitive nitrogenase of Gloeocapsa might be protected from photosynthetically produced oxygen were also examined. Gloeocapsa can remove toxic products derived from oxygen, such as superoxide and hydrogen peroxide, but it proved difficult to assess the role of this system under normal conditions of growth. Indeed, it is possible that it is a combination of several mechanisms which prevents nitrogenase from inactivation by oxygen.