Abstract :
[en] Cyanobacteria can proliferate to high cell densities (blooms) in lakes, (artificial) ponds or closed-system cultures and are used as dietary supplements. Certain cyanobacterial species are also capable of producing toxins, for instance, hepatotoxins (e.g., microcystins, nodularin and cylindrospermopsin) or neurotoxins (e.g., anatoxin-a and saxitoxin). During a screening for eight microcystin congeners (MCs) and nodularin in cyanobacteria- and Chlorella-based dietary supplements sold on the Belgium market, nine products were found to be contaminated. These products should only contain harvested Aphanizomenon flos-aquae, a species that blooms in the Upper Klamath Lake (South Oregon, US)1. As it is not clear if this species can produce MCs, the possible occurrence of other species in the blooms could be responsible for the MCs presence.
After quantifying the MCs with a validated LC-MS/MS method, the presence of genes involved in the production of MCs was tested. The mcyE gene was amplified using PCR and sequenced by the Sanger method.
MCs concentrations ranged between 39.7 and 4837.4 µg/kg MC-LR equivalent. Two dietary supplements contained concentrations higher than 1 µg/kg MC-LR equivalent which is proposed as regulatory limit by Gilroy et al.2. The phylogenetic affiliation of the mcyE sequences could be traced back to Microcystis sp. for seven products. The contamination of the supplements might be explained by the presence of Microcystis during the harvest of A. flos-aquae dominated blooms, as already observed in the past2.
1. Carmichael, et al., J. Appl. Phycol. 12, 585–595 (2000).
2. Gilroy, et al., Environ. Health Perspect. 108, 435–439 (2000).
