Toxin production by Microcystis

摘要

The worldwide occurrence and distribution of toxic cyanobacteria, especially in disturbed aquatic ecosystems, attests to their success in colonizing, and the occurrence of blooms have become common. Often they are harmful because of production of secondary metabolites, broadly referred to as "cyanotoxins". The ubiquitous genus Microcystis, which produces the toxin microcystin, reportedly contains non-toxic and toxic strains. Toxicity is affected by various environmental factors, such as temperature and light (van der Westhuizen & Eloff 1985), and nutrients, especially N (Carmichael 1986). Meissner et al. (1996) concluded it is unclear why certain strains of Microcystis aeruginosa are able to produce toxins, whereas others cannot. Grobbelaar & van den Heever (2002) found that various photosynthetic parameters gave no indication of potential toxicity of thirteen strains tested. Although the molecular basis of toxin production in M. aeruginosa has been partially determined, it is still not clear when a strain could be toxic or not. A peptide syn-thetase, termed mcyB, was positively identified as a role-player in microcystin-LR production in strain PCC 7806 (Dittmann et al. 1997).