Planktothrix

Planktothrix is a diverse genus of filamentous cyanobacteria observed to amass in algal blooms in water ecosystems across the globe. Like all Oscillatoriales, Planktothrix species have no heterocysts and no akinetes. Planktothrix are unique because they have trichomes and contain gas vacuoles unlike typical planktonic organisms. Previously, some species of the taxon were grouped within the genus Oscillatoria, but recent work has defined Planktothrix as its own genus. 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 which gives these organisms the ability to synthesize toxins has been sequenced. P. agardhii is an example of a type species of the genus. P. agardhii and P. rubescens are commonly observed in lakes of the Northern Hemisphere where they are known producers of potent hepatotoxins called microcystins.thumb|288x288px|Planktothrix rubescens culture. Note the reddish brown color which gave this strain's algal blooms the name "Burgundy-blood phenomenon"

thumb|288x288px|Planktothrix rubescens == Habitats and niches == Both P. agardhii and P. rubescens have the ability to form massive blooms in freshwater lakes and reservoirs. The whole genus has been studied to thrive in various temperate to subtropical water ecosystems in Europe, Asia, Africa and Australia. P. agardhii is commonly found at most latitudes in shallow and turbid lakes where it can tolerate continuous mixing of the water column. P. rubescens is regularly found in clear, deep alpine and pre-alpine lakes that are seasonally stratified. P. agardhii grows in the low light conditions of the metalimnion where it can maximize the absorption of green light with its phycoerythrin pigments. Under the action of wind-induced internal waves, P. rubescens can be moved vertically by several meters following the movements of the metalimnion, which in turn modifies rapidly (within a day) the light conditions experienced by the filaments. This was shown to significantly affect the photosynthesis rate and oxygen production especially in lakes where the dominant organism of the phytoplankton community is P. rubescens such as in Lake Zurich.