Organisms belonging to the genus Planktothrix (Anagnostidis et Komárek) are planktonic filamentous cyanobacteria with abundant gas vacuoles. Their cells are shorter than broad or isodiametric and their trichomes exhibit gliding motility by rotation. Usually sheaths are not produced, and their cell diameter ranges from 3.5 - 10 µm.
These organisms are mostly found in eutrophic or hypereutrophic freshwater lakes. They might form clusters and some produce water blooms. Most species grow in temperate lakes with only two species in the tropics. The conditions in the water column that favour the growth of Planktothrix have been extensively characterised by Walsby and co-workers (Bright and Walsby 2000, Davis and Walsby 2002, Davis et al. 2003).
Members of Planktothrix are regularly found to produce the hepatotoxin microcystin Genes involved in the biosynthesis such toxic cyclic peptides have been characterized for some species of Planktothrix and other cyanobacteria (Dittmann et al. 2001; Christiansen et al. 2003; Kurmayer et al. 2005). Recent studies have shown that species of Planktothrix produce potent toxins in addition to the well-characterised microcystin (e.g. Keil et al. 2001; Blom et al. 2003), however, the genetic basis of non-peptide toxin synthesis is poorly understood.
Bright D. I. and A. E. Walsby (2000) The daily integral of growth by Planktothrix rubescens calculated from growth rate in culture and irradiance in Lake Zürich. New Phytologist 146: 3001-316.
Christiansen G. J. Fastner, M. Erhard, T. Börner, and E. Dittmann. (2003) Microcystin Biosynthesis in Planktothrix: Genes, Evolution, and Manipulation. Journal of Bacteriology 185: 564-572.
Davis P.A. and A. E. Walsby (2002) Comparison of measured growth rates with those calculated from rates of photosynthesis in Planktothrix spp. isolated from Bleham Tarn, English Lake District. New Phytologist 156:225-239
Davis P. A. and M. Dent, J. Parker, C.S. Reynolds and A.E. Walsby (2003) The annual cycle of growth rate and biomas change in Planktothrix spp. in Blelham Tarn, English Lake District. Freshwater Biology 48:852-867
Dittmann E., M. Erhard, M. Kaebernick (2001) Altered expression of two light dependent genes in a microcystin-lacking mutant of Microcystis aueruginosa PCC7806. Microbiology 147:3113-3119
Kurmayer R., G. Christiansen, M. Gumpenberger and J. Fastner (2005) Genetic identification of microcystin ecotypes in toxic cyanobacteria of the genues Planktothrix. Microbiology 151:1525-1533