Ca requirement for aerobic nitrogen fixation by heterocystous blue-green algae |
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| Authors: | Rodríguez H Rivas J Guerrero M G Losada M |
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| Affiliation: | Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-Consejo Superior de Investigaciones Científicas, Apartado 1113, 41080 Sevilla, Spain. |
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| Abstract: | The requirement of Ca2+ for growth and nitrogen fixation has been investigated in two strains of heterocystous blue-green algae (Anabaena sp. and Anabaena ATCC 33047). With combined nitrogen (nitrate or ammonium) or with N2 under microaerobic conditions, Ca2+ was not required for growth, at least in concentrations greater than traces. In contrast, Ca2+ was required as a macronutrient for growth and nitrogen fixation with air as the nitrogen source. Addition of Ca2+ to an aerobic culture without Ca2+ promoted, after a lag of several hours, development of nitrogenase activity and cell growth. Provision of air to a microaerobic culture in the absence of Ca2+ promoted a drastic drop in nitrogenase activity, which rapidly recovered its initial level upon restoration of microaerobic conditions. Development of nitrogenase activity in response to either Ca2+ or low oxygen tension was dependent on de novo protein synthesis. The role of Ca2+ seems to be related to protection of nitrogenase from inactivation, by conferring heterocysts resistance to oxygen. |
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