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''Anabaena circinalis'' is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in '' A. circinalis '' owes to its production of several potentially harmful cyanotoxins, ranging in potency from irritating to lethal. Under favorable conditions for growth, '' A. circinalis '' forms large algae-like blooms, potentially harming the flora and fauna of an area. == Morphology == ''Anabaena circinalis'' exhibits a filamentous morphology, each filament a string of task-specific cells. The appearance of cell differentiation was a great evolutionary leap; marking cyanobacteria as one of the first multicellular organisms on Earth. On the '' A. circinalis '' filament, the most numerous structures are vegetative cells, responsible for the photosynthesis of high-energy sugars from environmental carbon, water, and sunlight. The energy from photosynthesis is used, in part, for the biosynthesis of cellular materials from nitrogenous compounds. During periods when combined nitrogen (e.g. ammonia or nitrate) is unavailable, '' A. circinalis '' form heterocysts, larger, round, nitrogen-fixing cells found every ten to twenty cells or so on the filament. Heterocysts function to convert environmental nitrogen (N2) into compounds such as ammonia or nitrate. Nitrogenase, an oxygen-sensitive enzyme, is essential to this conversion. For the proper functioning of nitrogenase, the intracellular environment of the heterocyst must be anaerobic, a task achieved by the oxygen-impermeable structure of the heterocyst wall. Although functioning independent of each other, vegetative cells and heterocysts are both essential to the survival of the organism; vegetative cells providing energy-rich sugars to the organism, while heterocysts fix nitrogen for amino acid production and cellular biosynthesis. Also found along the filaments are gas vacuoles, specialized compartments that inflate or deflate with air to provide upward or downward movement. This adaptation positions '' A. circinalis '' at a favorable depth, determined by available sunlight, water temperature, or O2 concentration. With optimal environmental conditions, '' Anabaena circinalis '' grow unchecked, forming large blooms that appear as a greenish slime at the surface of the water (fig. 2). In harsh conditions, '' A. circinalis '' form spore-like cells called akinetes. sturdy composition of akinetes are resistant to low temperature, desiccation, and darkness. Often, akinetes will hibernate in sediment until environmental conditions allow germination and re-growth. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Anabaena circinalis」の詳細全文を読む スポンサード リンク
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