ABSTRACT
Cyanobacteria (blue-green algae) are an ancient group of microorganisms that thrive in a broad spectrum of terrestrial, freshwater, and marine habitats ranging from hot springs to frozen ponds [1]. The successful colonization of this wide range of environments by cyanobacteria is linked to their long evolutionary history and adaptation to a number of environmental stresses such as high solar UV radiation, extreme temperatures, desiccation, oxidative stress, and nutrient uctuations. Present-day cyanobacteria perform oxygenic photosynthesis and possess chlorophyll a and water-soluble phycobilin proteins [2,3]. Additionally, certain members of this order are capable of xing atmospheric dinitrogen gas (N2), allowing them to colonize environments lacking a stable supply of xed nitrogen [2]. A range of environmental conditions including higher temperatures and pH values, low turbulence, and high nutrient levels (eutrophication) can result in the proliferation of planktonic cyanobacteria in lakes and reservoirs, often leading to the formation of huge surface blooms. Certain bloom-forming cyanobacteria are also capable of producing secondary metabolites, which have a range of bioactivities, some of which are highly toxic to eukaryotic organisms including humans. Cyanotoxins are very diverse in terms of their chemical structure as well as their toxicity [4-7]. Based on the toxic effects
18.1 Introduction .......................................................................................................................... 341 18.2 Microcystin ........................................................................................................................... 342
18.2.1 Biosynthesis .............................................................................................................. 343 18.2.2 Regulation .................................................................................................................344 18.2.3 Structural Variants ....................................................................................................344
