Cellular Factors Affecting Nitrogen Fixation in the Blue-Green Alga Chlorogloea fritschii

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Abstract
Synchronous cultures of a nitrogen-fixing blue-green alga, hitherto known as Chlorogloea fritschii but more probably an anomalous species of the genus Nostoc, were obtained by a combination of light and temperature treatments. Variation in dimensions, dry weight, pigment content and total nitrogen content of cells was followed during the development of synchronous cultures. The nitrogen-fixing activity was greatest in the small-celled filaments which develop from the endospores and predominate during exponential growth of the alga in cultures of limited volume. Strains of the alga produced by repeated exposure to X-rays, ultraviolet radiation, or sub-lethal concentrations of colchicine or urethane, were found to have lower rates of nitrogen fixation per unit dry weight than the original strain but liberated relatively more extracellular nitrogenous products.

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