subtropic. Planktothrix grow by cell division in a single plane to form unbranched structures of average length around 4 μm, but unlike other Oscillatoriales, these trichomes are phototactic. Typically, Planktothrix filaments do not have specialized cells such as akinetes or heterocysts, and do not produce mucilaginous envelopes, except for some rare species but only under stress conditions. Several species possess constant ratio of their two main photosynthetic pigments, i.e., phycocyanins and phycoerythrins. The production of cyanotoxins is facultative, and strains that do not produce microcystins are commonly found in nature. Apart from microcystins, they can produce several other cyclic peptides including oscillapeptin J. Planktothrix organisms house gas vesicles called protoplasts which play an important role in their buoyancy as the gas within the vesicle is nearly only one tenth the density of water making the organism less dense overall. Taxonomy The Plantothrix genus emerged as a cyanobacteria observed to form blooms at the surface of freshwater and organisms with the current classification were once categorized under the genus Oscillatoria. Mechanisms and toxicology Planktothrix organisms are able to store nitrogen as a co-polymer of aspartate and arginine which allows them to survive even under limited nitrogen supply from the atmosphere. This mechanism is also what allows thick blooms to prosper as the thicker the bloom, deeper Planktothrix are exposed to less light and atmospheric air. The increasing impact of algal blooms has been theorized to be connected to global warming caused by human activity. Harmful algal blooms caused by not only Planktothrix but also other forms of cyanobacteria including Dolichospermum (Anabaena) or Microcystis have correlation to toxic effects for humans leading to devastating impacts to agriculture. Planktothrix have the ability to produce cyanotoxins including microcystins, anatoxins, and saxitoxins. Strains P. agardhii (Gomont) Anagnostidis et Komárek 1988 P. rubescens (de Candolle ex Gomont) Anagnostidis et Komárek 1988 P. isothrix (Skuja) Komárek et Komárková 2004 [[P. prolifica]] P. mougeotii P. paucivesiculata P. pseudagardhii''P. spiroidesP. sertaP. tepida'' See also Algal blooms Anabaena Microcystins Microcystis References Cyanobacteria genera Oscillatoriales