cyanobacteria

Single-celled, primitive organisms that resemble bacteria in their internal cell organization, sometimes joined together in colonies or filaments. Cyanobacteria are among the oldest known living organisms and, with bacteria, belong to the kingdom Monera; remains have been found in rocks up to 3.5 billion years old. They are widely distributed in aquatic habitats, on the damp surfaces of rocks and trees, and in the soil.

Cyanobacteria and bacteria are prokaryotic organisms. Some can fix nitrogen and thus are necessary to the nitrogen cycle, while others follow a symbiotic existence – for example, living in association with fungi to form lichens. Fresh water can become polluted by nitrates and phosphates from fertilizers and detergents. This eutrophication, or overenrichment, of the water causes multiplication of the cyanobacteria in the form of cyanobacterial blooms. The cyanobacteria multiply and cover the water's surface, remaining harmless until they give off toxins as they decay. These toxins kill fish and other wildlife and can be harmful to domestic animals, cattle, and people.

In 1996 Japanese researchers sequenced the genome of the cyanobacterium Synechosystis. It has 3.57 million bases and was the first photosynthetic organism to have its genome sequenced. German researchers revealed in 1998 how cyanobacteria move around. They shoot minuscule threads of slime from pores and use these to push themselves through fluid.