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Cyanobacteria are photosynthetic bacteria that share some properties with algae and are found naturally in lakes, streams, ponds, and other surface waters. Cyanobacteria can rapidly multiply in surface water and cause “blooms.” Several types of cyanobacteria, for example Anabaena sp have gas-filled cavities that allow them to float to the surface or to different levels below the surface, depending on light conditions and nutrient levels. This can cause the cyanobacteria to concentrate on the water surface, causing a pea-soup green color or blue-green “scum.” Some cyanobacteria like Planktothrix sp, can be found in bottom sediments and float to the surface when mobilized by storm events or other sediment disturbances. Other cyanobacteria blooms may remain dispersed through the water column (Cylindrospermopsis sp.) leading to a generalized discoloration of the water.
Although a variety of techniques have been developed to control cyanobacterial blooms and remove cyanobacterial cells or metabolites in water treatment processes, the effect of these treatments on the membrane integrity of cyanobacterial cells have not been systematically studied and compared.
Cyanobacterial blooms can be harmful to the environment, animals, and human health. The bloom decay consumes oxygen, creating hypoxic conditions which result in plant and animal death. Under favorable conditions of light and nutrients, some species of cyanobacteria produce toxic secondary metabolites, known as cyanotoxins. Common toxin-producing cyanobacteria are Microcystis, Anabaena, Planktothrix, Anabaenopsis, Aphanizomenon (producing microcystin – LR), Cylindrospermopsis, Aphanizomenon, Anabaena, Lyngbya, Rhaphidiopsis, Umezakia (producing Cylindrospermopsin), Anabaena, Planktothrix, Aphanizomenon, Cylindrospermopsis, Oscillatoria (producing anatoxins).The conditions that cause cyanobacteria to produce cyanotoxins are not well understood. Some species with the ability to produce toxins may not produce them under all conditions. These species are often members of the common bloom-forming genera. Both nontoxic and toxic varieties of most of the common toxin-producing cyanobacteria exist, and it is impossible to tell if a species is toxic or non toxic by looking at it. Also, even when toxin producing cyanobacteria are present, they may not actually produce toxins. Furthermore, some species of cyanobacteria can produce multiple types and variants of cyanotoxins. Molecular tests are available to determine if the cyanobacteria,
Microcystis for example, carry the toxin gene; quantitative cyanotoxin analysis is needed to determine if the cyanobacteria are actually producing the toxin. Water contaminated with cyanobacteria can occur without associated taste and odor problems. In most cases, the cyanobacterial toxins naturally exist intracellularly (in the cytoplasm) and are retained within the cell. Anatoxin-a and the microcystin variants are found intracellularly approximately 95% of the time during the growth stage of the bloom. For those species, when the cell dies or the cell membrane ruptures the toxins are released into the water (extracellular toxins). However, in other species, Cylindrospermopsin for example, a significant amount of the toxin may be naturally released to the water by the live cyanobacterial cell. Extracellular toxins may adsorb to clays and organic material in the water column and are generally more difficult to remove than the intracellular toxins.
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