Cellular Characteristics
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Cyanobacteria were formerly classified as blue-gree algae (les algues bleues in French, las algas azules in
Spanish) because of their algal-like appearance, their possession of chlorophyll rather than bacteriochlorophyll,
and their photosynthetic production of oxygen by a two-photosystem process as in algae and higher
plants. The most widely used taxonomic schemes for these organisms are largely based on the International
Botanical Code, with separation according to classic morphological criteria. Ultrastructural studies,
however, clearly show that the Cyanobacteria are prokaryotic; that is, they lack nuclei and other organelles
and they have a peptidoglycan cell wall that is typical of gram-negative Eubacteria. They also
possess several features that set them apart from other bacteria, especially their photosynthetic apparatus
and oxygen production. The term ‘blue-green algae’ is still widely used by the media and in the
water quality management area. The current taxonomic separation of species, especially the coccoid
and nonheterocystous (see definition later) taxa, is believed to be artificial and not reflective of evolutionary
relationships, and will likely be substantially revised as more genetic data become available.