Occurrence and toxicity of cyanobacterium Microcystis aeruginosa in freshwater ecosystems of the Indian subcontinent: a review

Microcystis aeruginosa is a common freshwater cyanobacterium inflicting a potentially detrimental effect on aquatic and terrestrial life forms due to their bloom formation and production of hepatotoxin called Microcystin. Although several cases of human and animal poisoning associated with Microcystis aeruginosa bloom have been reported worldwide, there are only a few studies or bloom reports, particularly in Indian aquatic systems. Frequent occurrences of such toxic Microcystis blooms are a threat to water quality as well as the health of humans and animals. Increased cultural eutrophication and varying climatic conditions have intensified the incidents of Microcystis blooms in different waterbodies, most of which remain undocumented. The complexity of the ecology of bloom formers and variables affecting bloom formation and toxin production limits the complete understanding of microalgal blooms. The potential environmental and health risks caused by Microcystis blooms and their toxins make them an ecologically and economically important species. Hence, a holistic understanding of the effects of Microcystis blooms, dynamics, and their toxicity is inevitable. Therefore, this review recapitulates the toxic freshwater cyanobacteria Microcystis, briefly emphasising the occurrence of Microcystis bloom reports along the Indian waters, factors catalysing the bloom formation and its related toxicity studies. This review further provides an overview of the life cycle of Microcystis species, the toxic effects of Microcystin and its mode of action.