Temporal variations in the dynamics of potentially microcystin-producing strains in a bloom-forming Planktothrix agardhii (Cyanobacterium) population.
The concentration of microcystins (MCs) produced during blooms depends on variations in both the proportion of strains containing the genes involved in MC production and the MC cell quota (the ratio between the MC concentration and the density of cells with the mcyA genotype) for toxic strains. In order to assess the dynamics of MC-producing and non-MC-producing strains and to identify the impact of environmental factors on the relative proportions of these two subpopulations, we performed a 2-year survey of a perennial bloom of Planktothrix agardhii (cyanobacteria). Applying quantitative real-time PCR to the mcyA and phycocyanin genes, we found that the proportion of cells with the mcyA genotype varied considerably over time (ranging from 30 to 80% of the population). The changes in the proportion of cells with the mcyA genotype appeared to be inversely correlated to changes in the density of P. agardhii cells and also, to a lesser extent, to the availability of certain nutrients and the abundance of cladocerans. Among toxic cells, the MC cell quota varied throughout the survey. However, a negative correlation between the MC cell quota and the mcyA cell number during two short periods characterized by marked changes in the cyanobacterial biomass was found. Finally, only 54% of the variation in the MC concentrations measured in the lake can be explained by the dynamics of the density of cells with the MC producer genotype, suggesting that this measurement is not a satisfactory method for use in monitoring programs intended to predict the toxic risk associated with cyanobacterial proliferation.
Briand
Enora
E
MNHN, USM505/EA4105 Ecosystèmes et Interactions Toxiques, 57 rue Cuvier, case 39, 75231 Paris Cedex 05, France.
Gugger
Muriel
M
François
Jean-Christophe
JC
Bernard
Cécile
C
Humbert
Jean-François
JF
Quiblier
Catherine
C
D000818:Animals; D033361:Cladocera / Q000382:microbiology; D015169:Colony Count, Microbial; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D052998:Microcystins / Q000096:biosynthesis* / Q000235:genetics; D010798:Phycocyanin / Q000235:genetics; D010839:Phytoplankton / Q000254:growth & development; D016133:Polymerase Chain Reaction / Q000379:methods; D013696:Temperature; D013997:Time Factors; D015048:Zooplankton / Q000254:growth & development
D004269:DNA, Bacterial; D052998:Microcystins; D010798:Phycocyanin; C078588:microcystin