title: Toxic cyanobacterial bloom triggers in missisquoi bay, lake champlain, as determined by next-generation sequencing and quantitative PCR.
abstract: Missisquoi Bay (MB) is a temperate eutrophic freshwater lake that frequently experiences toxic Microcystis-dominated cyanobacterial blooms. Non-point sources are responsible for the high concentrations of phosphorus and nitrogen in the bay. This study combined data from environmental parameters, E. coli counts, high-throughput sequencing of 16S rRNA gene amplicons, quantitative PCR (16S rRNA and mcyD genes) and toxin analyses to identify the main bloom-promoting factors. In 2009, nutrient concentrations correlated with E. coli counts, abundance of total cyanobacterial cells, Microcystis 16S rRNA and mcyD genes and intracellular microcystin. Total and dissolved phosphorus also correlated significantly with rainfall. The major cyanobacterial taxa were members of the orders Chroococcales and Nostocales. The genus Microcystis was the main mcyD-carrier and main microcystin producer. Our results suggested that increasing nutrient concentrations and total nitrogen:total phosphorus (TN:TP) ratios approaching 11:1, coupled with an increase in temperature, promoted Microcystis-dominated toxic blooms. Although the importance of nutrient ratios and absolute concentrations on cyanobacterial and Microcystis dynamics have been documented in other laboratories, an optimum TN:TP ratio for Microcystis dominance has not been previously observed in situ. This observation provides further support that nutrient ratios are an important determinant of species composition in natural phytoplankton assemblages.
authors.affiliation: National Research Council Canada, Energy, Mining and Environment, 6100 Royalmount Avenue, Montreal, QC H4P 2R2, Canada. nathalie.fortin@cnrc-nrc.gc.ca.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fortin
authors.affiliation: National Research Council Canada, Energy, Mining and Environment, 6100 Royalmount Avenue, Montreal, QC H4P 2R2, Canada. valentina.munozramos@mail.mcgill.ca.
authors.forename: Valentina
authors.initials: V
authors.lastname: Munoz-Ramos
authors.affiliation: Faculté des sciences, Université du Québec à Montréal, Case postale 8888, Succ Centre-ville, Montreal, QC H3C 3P8, Canada. bird.david@uqam.ca.
authors.forename: David
authors.initials: D
authors.lastname: Bird
authors.affiliation: Faculté de médecine, Université Laval, 945 Ave. Wolfe, Quebec City, QC G1V 5B3, Canada. benoit.levesque@inspq.qc.ca.|Institut national de santé publique du Québec, 945 Ave. Wolfe, Quebec City, QC G1V 5B3, Canada. benoit.levesque@inspq.qc.ca.
authors.forename: Benoît
authors.initials: B
authors.lastname: Lévesque
authors.affiliation: Department of Natural Resource Sciences, McGill University, 21,111 Lakeshore Road, St. Anne de Bellevue, QC, H9X 3V9, Canada. lyle.whyte@mcgill.ca.
authors.forename: Lyle G
authors.initials: LG
authors.lastname: Whyte
authors.affiliation: National Research Council Canada, Energy, Mining and Environment, 6100 Royalmount Avenue, Montreal, QC H4P 2R2, Canada. charles.greer@cnrc-nrc.gc.ca.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Greer
keywords: E. coli; Microcystis; cyanobacteria; next-generation sequencing; nutrient ratio; quantitative PCR