Kingdom Monera: The Cyanobacteria The autotrophic (auto = "self" tropho = "nourishment", Greek) cyanobacteria were once classified as "blue green algae" because of their superficial resemblance to eukaryotic green algae. Although both groups are photosynthetic, they are only distantly related: cyanobacteria lack internal organelles, a discrete nucleus and the proteins associated with eukaryotic chromosomes. Like all eubacteria, their cell walls contain peptidoglycan. Because motile species of cyanobacteria utilize the same mysterious gliding locomotion as the gram-negative gliding bacteria, some microbiologists suggest that cyanobacteria should be classified together as a subgroup of gliding bacteria. Although they are truly prokaryotic, cyanobacteria have an elaborate and highly organized system of internal membranes which function in photosynthesis. Chlorophyll is embedded in these photosynthetic membranes. The photosynthetic pigments impart a rainbow of possible colors: yellow, red, violet, green, deep blue and blue-green cyanobacteria are known. Cyanobacteria may be single-celled or colonial. Depending upon the species and environmental conditions, colonies may form filaments, sheets or even hollow balls. Some species are able to "fix" nitrogen gas, which cannot be absorbed by plants, into nitrogen compounds which can be absorbed by much like a fertilizer. The rice paddies of Asia, which feed about 75% of the world's human population, could not do so were it not for healthy populations of nitrogen-fixing cyanobacteria in the rice paddy waters. Found in almost every conceivable habitat, from oceans to fresh water to bare rock to soil, cyanobacteria produce the compounds responsible for "earthy" odors we detect in soil and some bodies of water (such as those being cyanobacterially cleaned at water treatment plants). The greenish slime on the side of your damp flower pot, the wall of your house or the trunk of that big tree is more likely to be cyanobacteria than anything else. Cyanobacteria have even been found on the fur of polar bears, to which they impart a greenish tinge! Virus and Bacteria Unit .