Cellular factors affecting nitrogen fixation in the blue-green alga Chlorogloea fritschii

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 sublethal 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.