title: Effect of light intensity on the relative dominance of toxigenic and nontoxigenic strains of Microcystis aeruginosa.
abstract: In aquatic ecosystems, the factors that regulate the dominance of toxin-producing cyanobacteria over non-toxin-producing strains of the same species are largely unknown. One possible hypothesis is that limiting resources lead to the dominance of the latter because of the metabolic costs associated with toxin production. In this study, we tested the effect of light intensity on the performance of a microcystin-producing strain of Microcystis aeruginosa (UTCC 300) when grown in mixed cultures with non-microcystin-producing strains with similar intrinsic growth rates (UTCC 632 and UTCC 633). The endpoints measured included culture growth rates, microcystin concentrations and composition, and mcyD gene copy numbers determined using quantitative PCR (Q-PCR). In contrast to the predicted results, under conditions of low light intensity (20 μmol·m(-2)·s(-1)), the toxigenic strain became dominant in both of the mixed cultures based on gene copy numbers and microcystin concentrations. When grown under conditions of high light intensity (80 μmol·m(-2)·s(-1)), the toxigenic strain still appeared to dominate over nontoxigenic strain UTCC 632 but less so over strain UTCC 633. Microcystins may not be so costly to produce that toxigenic cyanobacteria are at a disadvantage in competition for limiting resources.
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada. serenaud@gmail.com
authors.forename: Susan
authors.initials: S
authors.lastname: Leblanc Renaud
authors.forename: Frances R
authors.initials: FR
authors.lastname: Pick
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fortin
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D008027:Light; D052998:Microcystins / Q000096:biosynthesis*; D046931:Microcystis / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D060888:Real-Time Polymerase Chain Reaction; D014871:Water Microbiology
chemical_list: D004269:DNA, Bacterial; D052998:Microcystins; C078588:microcystin