Towards clarification of the biological role of microcystins, a family of cyanobacterial toxins

Abstract

Microcystins constitute a serious threat to the quality of drinking water worldwide. These protein phosphatase inhibitors are formed by various cyanobacterial species, including Microcystis sp. Microcystins are produced by a complex microcystin synthetase, composed of peptide synthetases and polyketide synthases, encoded by the mcyA-J gene cluster. Recent phylogenetic analysis suggested that the microcystin synthetase predated the metazoan lineage, thus dismissing the possibility that microcystins emerged as a means of defence against grazing, and their original biological role is not clear. We show that lysis of Microcystis cells, either mechanically or because of various stress conditions, induced massive accumulation of McyB and enhanced the production of microcystins in the remaining Microcystis cells. A rise in McyB content was also observed following exposure to microcystin or the protease inhibitors micropeptin and microginin, also produced by Microcystis. The extent of the stimulation by cell extract was strongly affected by the age of the treated Microcystis culture. Older cultures, or those recently diluted from stock cultures, hardly responded to the components in the cell extract. We propose that lysis of a fraction of the Microcystis population is sensed by the rest of the cells because of the release of non-ribosomal peptides. The remaining cells respond by raising their ability to produce microcystins thereby enhancing their fitness in their ecological niche, because of their toxicity.

Towards clarification of the inhibitory mechanism of wheat bran leachate on Microcystis aeruginosa NIES-843 (cyanobacteria): physiological responses

“…Cell lysis of M. aeruginosa NIES-843 was microscopically observed under the WBL stress in this study (Fig. 5), and this kind of cellular lysis in M. aeruginosa NIES-843 cells may be the reason for the up-regulated expression of mcyB under WBL stress, similar to the report by Schatz et al (2007).…”

“…Kaebernick et al (2000) found that transcript levels of both mcyB and mcyD up-regulated under high light intensities and red light. Schatz et al (2007) found cellular lysis of Microcystis induced massive accumulation of McyB and enhanced the production of microcystins in the remaining Microcystis cells, and therefore proposed that releasing microcystins from lytic cells act as info-chemicals to stimulate microcystins biosynthesis and thereby enhancing their fitness in their ecological niche. Cell lysis of M. aeruginosa NIES-843 was microscopically observed under the WBL stress in this study (Fig.…”

Effects of microcystin-producing and microcystin-free strains ofPlanktothrix agardhiion long-term population dynamics ofDaphnia magna

“…Indeed, the production of toxic metabolites is suspected to alter biotic communities through allelopathic interactions. Several hypotheses have been proposed concerning the role of such metabolites at several trophic levels (for reviews, see Vasconcelos and Pereira, 2001;Gross, 2003;Wiegand and Pflugmacher, 2005;Babica et al, 2006;Leflaive and TenHage, 2007;Schatz et al, 2007). However, such a toxic activity is difficult to characterize because of (i) the presence of other molecules that may modify the effect of toxins (Rohrlack et al, 1999b;Buryskova et al, 2006), (ii) the adaptation of target organisms (Wilson and Hay, 2007) and (iii) the appearance of avoidance behaviour in some species of zooplankton (Kurmayer and Ju¨ttner, 1999).…”

Synergistic allelochemicals from a freshwater cyanobacterium

“…4,5). However, in general the ecological role played by the majority of these metabolites is not well known (6,7). Functions established to date for cyanobacterial secondary metabolites include nitrogen storage (8), UV protection (9), metal chelation (10), defense against predation (11), and quorum sensing (12).…”