title: The microcystin composition of the cyanobacterium Planktothrix agardhii changes toward a more toxic variant with increasing light intensity.
abstract: The cyanobacterium Planktothrix agardhii, which is dominant in many shallow eutrophic lakes, can produce hepatotoxic microcystins. Currently, more than 70 different microcystin variants have been described, which differ in toxicity. In this study, the effect of photon irradiance on the production of different microcystin variants by P. agardhii was investigated using light-limited turbidostats. Both the amount of the mRNA transcript of the mcyA gene and the total microcystin production rate increased with photon irradiance up to 60 micromol m(-2) s(-1), but they started to decrease with irradiance greater than 100 micromol m(-2) s(-1). The cellular content of total microcystin remained constant, independent of the irradiance. However, of the two main microcystin variants detected in P. agardhii, the microcystin-DeRR content decreased twofold with increased photon irradiance, whereas the microcystin-DeLR content increased threefold. Since microcystin-DeLR is considerably more toxic than microcystin-DeRR, this implies that P. agardhii becomes more toxic at high light intensities.
authors.affiliation: Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands. ltonk@science.uva.nl
authors.forename: Linda
authors.initials: L
authors.lastname: Tonk
authors.forename: Petra M
authors.initials: PM
authors.lastname: Visser
authors.forename: Guntram
authors.initials: G
authors.lastname: Christiansen
authors.forename: Elke
authors.initials: E
authors.lastname: Dittmann
authors.forename: Eveline O F M
authors.initials: EO
authors.lastname: Snelder
authors.forename: Claudia
authors.initials: C
authors.lastname: Wiedner
authors.forename: Luuc R
authors.initials: LR
authors.lastname: Mur
authors.forename: Jef
authors.initials: J
authors.lastname: Huisman
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism / Q000633:toxicity; D003470:Culture Media; D000458:Cyanobacteria / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D003624:Darkness; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D052998:Microcystins; D010456:Peptides, Cyclic / Q000235:genetics / Q000378:metabolism / Q000633:toxicity*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003470:Culture Media; D052998:Microcystins; D010456:Peptides, Cyclic; D012333:RNA, Messenger; C078588:microcystin