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Planktothrix
''Planktothrix'' is a genus of filamentous cyanobacteria (often called blue-green algae). ''P. agardhii'' is regarded as a type species of the genus.〔Komárek J, Komárková J (2004) Taxonomic review of the cyanoprokaryotic genera ''Planktothrix'' and ''Planktothricoides''. Czech Phycology 4:1–18 ()〕 Like all the Oscillatoriales, ''Planktothrix'' species have no heterocyst and no akinetes, but are unique because they are planktonic, solitary trichome and have gas vacuoles.〔Komarek J (2003) Planktic oscillatorialean cyanoprokaryotes (short review according to combined phenotype and molecular aspects). Hydrobiologia 502:367–382〕 Before the work of Suda et al.,〔Taxonomic revision of water-bloom-forming species of oscillatorioid cyanobacteria. Shoichiro Suda, Makoto M. Watanabe, Shigeto Otsuka, Aparat Mahakahant, Wichien Yongmanitchai, Napavarn Nopartnaraporn, Yongding Liu and John G. Day. ''International Journal of Systematic and Evolutionary Microbiology'' (2002), 52, 1577–1595 〕 some species of the taxon were grouped within the genus ''Oscillatoria''. A tremendous body of work on ''Planktothrix'' ecology and physiology has been done by Anthony E. Walsby, and the 55.6 kb microcystin synthetase gene have been sequenced.〔Christiansen G, Fastner J, Erhard M, Börner T, Dittmann E (2003) Microcystin biosynthesis in Planktothrix: genes, evolution, and manipulation. J Bacteriol 185:564–572 〕
''P. agardhii'' and ''P. rubescens'' are commonly observed in lakes of the Northern Hemisphere where they are known producers of potent hepatotoxins called microcystins.〔Sivonen, K., and G. Jones. 1999. Cyanobacterial toxins, p. 41–111. In: I. Chorus and J. Bertram (ed.), Toxic cyanobacteria in water: a guide to public health significance, monitoring and management. E&FN Spon, London ()〕
== Characteristics ==
Like most Oscillatoriales, ''Planktothrix'' grows by cell division in a single plane to form long unbranched trichomes (also called filaments) of length up to 4 mm, but unlike other Oscillatoriales, these trichomes are phototactic and slightly motile. 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.〔Ostermaier V, Kurmayer R (2009) Distribution and abundance of nontoxic mutants of cyanobacteria in lakes of the Alps. Microbial Ecology 58:1–11 〕 Apart from microcystins, they can to produce several other cyclic peptides, such as oscillapeptin J.〔Blom JF, Bister B, Bischoff D, Nicholson G, Jung G, Süssmuth RD, Jüttner F (2003) Oscillapeptin J, a new grazer toxin of the freshwater cyanobacterium Planktothrix rubescens. J Nat Prod 66:431–434〕
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