ABSTRACT
Cyanobacteria (blue-green algae) are photosynthetic prokaryotes with an oxygenic photosynthesis. Reproduction in cyanobacteria is generally by fission, budding, trichome breakage, hormogonia formation, or akinete germination. Cyanobacteria form symbiotic associations with plants, animals, nonphotosynthetic protists belonging to the group Glaucophyta, and bacteria. Among plants, cyanobacteria form symbiotic associations with algae (diatoms), fungi (lichens), bryophytes (liverworts, hornworts, and mosses), pteridophytes, gymnosperms, and angiosperme. In all other plant symbioses, the cyanobiont is a heterocystous filamentous cyanobacterium belonging to the genus Nostoc or Anabaena. Cyanobacterial-algal symbioses, together with the cyanobacterial symbioses with animals, glaucophytes, and bacteria. Two groups of animals are reported to have cyanobacterial symbionts: echiruoid worms and marine sponges. The bacterial symbionts are often concentrated around the heterocysts or the heterocysts-vegetative cell junctions. The incidence of symbiosis is very common in sponges occurring in the tropical marine environment and it has a fairly wide geographical distribution.
