Nine phycoerythrin-rich cyanobacteria were isolated from the blades of Sargassurn fluitans and S. natans. Aspects of their structure, metabolism and environmental physiology were studied. They were identified as belonging to the genus Oscillatoria. Four distinct
gross morphologies were observed in mass culture. High biomass yields were observed in batch culture, with dry weights up to 1.28 mg˙ml−1. All strains were rich in phycoerythrin, producing up to 13.30% by dry weight. The relationship between light intensity and photosynthetic
capacity was studied by measuring oxygen evolution, with rates of up to 0.522 moles O2˙(g˙chl a−1˙h−1) observed. No nitrogen fixation activity was observed in the light in the presence of oxygen. Four of the isolates demonstrated
nitrogen fixation activity under anaerobic and microaerobic conditions. Based on the results of these studies the isolates were categorized into six types. The significance of these cyanobacteria to the ecology of the Sargassurn community is discussed.
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