Cyanoprokaryota and Other Prokaryotic Algae

Cyanobacteria (blue-green algae) constitute the largest, most diverse, and most widely distributed group of photosynthetic prokaryotes. Although they lack organized chloroplast, their photosynthetic apparatus is remarkably similar in functional, structural, and molecular respects to that of higher plants and algae, with the exception of their light harvesting complex, which comprises phycobilline chromophores. Cyanobacteria are common in soil and in both salt and fresh water and can grow over a wide range of temperatures. Under proper conditions (including pollution by nitrogen wastes) they can rapidly proliferate, forming dense floating mats, called scums, usually colored opaque green. Notorious blooms of toxic cyanobacteria that jeopardize the supply of drinking water were recorded in recent years world wide. This chapter reviews aspects of the taxonomy, structure, diversity, metabolic activities, and physiological ecology of cyanobacteria and discusses their adaptation to inland water environments and the role they play in a wide range of aquatic ecosystems.