CYANOBACTERIAL SECONDARY METABOLITES

Abstract

Cyanobacteria inhabit a range of diverse and extreme habitats and have potential to
produce an elaborate array of secondary metabolites with unusual structures and potent
bioactivity. This review summarizes several classes of cyanobacterial secondary
metabolites some of which pose a threat to human or animal health in aquatic
ecosystems because of their acute toxicity. This class includes hepatotoxins (microcystins
and nodularins), neurotoxins (saxitoxin and anatoxins) and irritant toxins
(lipopolysachharides). Another important class includes the phytohormones (IAAs,
cytokinin and gibberillin-like compounds) and iron-chelators (schizokinen, anachelin and
synechobactins) which besides exerting profound effect on the productivity of the
ecosystem have also potential for use as medicine for treatment of persistent metal
toxicity. Several cyclic peptides and depsipeptides such as cyanopeptolins, micropeptin
and oscillaeptin which have been categorized as protease inhibitors make cyanobacteria
unattractive as a food source to grazers and help in their survival. UV-screening
compounds such as scytonemin and mycosporin-like amino acids (MAAs) produced by
cyanobacteria inhabiting habitats exposed to intense solar radiation may find use in
development of artificial sunscreens.