text: It has long been known that filamentous cyanobacteria perform surface motions, and that these movements result from type IV pili. Additionally, Synechococcus, a marine cyanobacteria, is known to swim at a speed of 25 μm/s by a mechanism different to that of bacterial flagella. Formation of waves on the cyanobacteria surface is thought to push surrounding water backwards. Cells are known to be motile by a gliding method and a novel uncharacterized, non-phototactic swimming method that does not involve flagellar motion.
  Many species of cyanobacteria are capable of gliding. Gliding is a form of cell movement that differs from crawling or swimming in that it does not rely on any obvious external organ or change in cell shape and it occurs only in the presence of a substrate. Gliding in filamentous cyanobacteria appears to be powered by a "slime jet" mechanism, in which the cells extrude a gel that expands quickly as it hydrates providing a propulsion force, although some unicellular cyanobacteria use type IV pili for gliding.
  Cyanobacteria have strict light requirements. Too little light can result in insufficient energy production, and in some species may cause the cells to resort to heterotrophic respiration. Too much light can inhibit the cells, decrease photosynthesis efficiency and cause damage by bleaching. UV radiation is especially deadly for cyanobacteria, with normal solar levels being significantly detrimental for these microorganisms in some cases.
  Filamentous cyanobacteria that live in microbial mats often migrate vertically and horizontally within the mat in order to find an optimal niche that balances their light requirements for photosynthesis against their sensitivity to photodamage. For example, the filamentous cyanobacteria Oscillatoria sp. and Spirulina subsalsa found in the hypersaline benthic mats of Guerrero Negro, Mexico migrate downwards into the lower layers during the day in order to escape the intense sunlight and then rise to the surface at dusk. In contrast, the population of Microcoleus chthonoplastes found in hypersaline mats in Camargue, France migrate to the upper layer of the mat during the day and are spread homogeneously through the mat at night. An in vitro experiment using Phormidium uncinatum also demonstrated this species' tendency to migrate in order to avoid damaging radiation. These migrations are usually the result of some sort of photomovement, although other forms of taxis can also play a role.
  Photomovement – the modulation of cell movement as a function of the incident light – is employed by the cyanobacteria as a means to find optimal light conditions in their environment. There are three types of photomovement: photokinesis, phototaxis and photophobic responses.
  Photokinetic microorganisms modulate their gliding speed according to the incident light intensity. For example, the speed with which Phormidium autumnale glides increases linearly with the incident light intensity.
  Phototactic microorganisms move according to the direction of the light within the environment, such that positively phototactic species will tend to move roughly parallel to the light and towards the light source. Species such as Phormidium uncinatum cannot steer directly towards the light, but rely on random collisions to orient themselves in the right direction, after which they tend to move more towards the light source. Others, such as Anabaena variabilis, can steer by bending the trichome.
  Finally, photophobic microorganisms respond to spatial and temporal light gradients. A step-up photophobic reaction occurs when an organism enters a brighter area field from a darker one and then reverses direction, thus avoiding the bright light. The opposite reaction, called a step-down reaction, occurs when an organism enters a dark area from a bright area and then reverses direction, thus remaining in the light.