Isolation and characterization of endosymbiotic Calothrix (Cyanophyceae) in Encephalartos hildebrandtii (Cycadales)

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Abstract
A Calothrix sp. has repeatedly been isolated from the surface-sterilized coralloid roots of Encephalartos hildebrandtii. Other coralloid root clusters on the same plant contained a Nostoc sp. as endophyte. All cyanobiont isolates were contaminated with Eubacteria. While growing inside the root, the endophyte morphologically does not resemble Calothrix, Nostoc or Anabaena. In culture, however, it did assume a typical Calothrix morphology. In the root, the endophyte had substantial nitrogenase activity although no heterocysts could be distinguished. In culture heterocysts and akinetes could be clearly identified, and cells did not contain phycoerythrinoid pigments. They exhibited catalase and urease activity and could grow in the dark with glucose, fructose or sucrose as the sole energy source.