Affinities of the Aphanocapsa feldmanni-like cyanobacteria from the marine sponge Xestospongia muta based on genetic and morphological analyses

The marine sponge Xestospongia muta (Porifera: Demospongiae: Haplosclerida) harbours cyanobacteria in its peripheral tissue that have been described as having an Aphanocapsa feldmanni-type appearance. Through subsequent cell fractionation steps we obtained a virtually pure cell suspension of the cyanobacteria. Through amplification of a region of the 16S rRNA gene we found that these cyanobacteria seem closely related to Prochlorococcus (Cyanobacteria, Prochlorophytes, Prochlorococcaceae), and Synechococcus (Cyanobacteria, Chroococcales, Synechococcus). We furthermore developed a new method, to obtain a clear signal with FISH by bleaching the
auto-fluorescence of cyanobacteria, with osmium tetroxide. The location and morphological characteristics of the cyanobacteria are described by both light and electron microscopy.