Microcystin production revisited: conjugate formation makes a major contribution

Abstract

The impact of environmental stimuli on the productionof the widespread cyanobacterial hepatotoxinmicrocystin (MC) is under debate. Whereas transcriptionalstudies of the biosynthetic genes suggest aclear influence of light conditions on toxin productionthe data for the metabolite itself are inconsistent andhighly strain-specific. Here, we have reassessed theMC content by using two immunological detectiontechniques that allow a parallel quantification of MCin the methanolic extracts and the residual pellet fractionthat contains high molecular weight proteins. Ourresults show a significant proportion of MC in theprotein bound fraction in strains of Microcystis andPlanktothrix and of the related toxin nodularin (NOD)in Nodularia. Moreover, we could show a very strongincrease of MC after high light illumination in theprotein fraction contributing to a significant overallincrease in MC production under these conditionsthat is not seen in extracts analysed by LC-MS andELISA. The fact that a considerable portion of MC isneglected with current analysis techniques was alsoconfirmed for selected field samples. Immunofluorescencestudies suggest strain-specific differences inthe amount of MC conjugate formation.Quelle: Environmental Microbiology (2013) 15(6), 1810-1820