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.

Characterising and predicting cyanobacterial blooms in an 8-year amplicon sequencing time course

“…For example, cyanobacterial growth is optimal at higher temperatures, between 15 and 30°C (Konopka and Brock, 1978). We confirmed that cyanobacterial blooms are correlated with and likely respond to nutrient concentrations, as previously described (Fogg, 1969;Jacoby et al, 2000;Paerl and Huisman, 2008;Paerl and Huisman, 2009;Fortin et al 2015;Isles et al, 2015). Dissolved nitrogen and temperature were negatively correlated, which could be explained by the fact that the lake becomes enriched in nitrates during spring, when temperatures are lower and rain and drainage bring nutrients into the lake (Shade et al, 2007;Fortin et al, 2015).…”

“…Between 50 and 250 ml of lake water was filtered depending on the density of the planktonic biomass using 0.2-μm hydrophilic polyethersulfone membranes (Millipore). Physico-chemical measurements, as described in Fortin et al (2015), were also taken during most sampling events . These environmental data included water temperature, average air temperature over one week, cumulative precipitation over one week, microcystin toxin concentration, total and dissolved nutrients (phosphorus and nitrogen).…”

“…An assemblage here is defined as a set of co-occurring OTUs. We defined bloom samples as described above, and trained the model with two different approaches: (i) with 2/3 of the total data, selected at random and (ii) with two distinctive years: 2007, a year with only a short-lived fall bloom and 2009, a year in which Fortin et al (2015) observed a high biomass of cyanobacteria during the summer. In the training stage, BIOMICO learns how OTU assemblages contribute to community structure and what assemblages tend to be present during blooms.…”

Temporal Dynamics of the Microbial Community Composition with a Focus on Toxic Cyanobacteria and Toxin Presence during Harmful Algal Blooms in Two South German Lakes

“…Molecular approaches outperform microscopy when estimating the diversity of heterotrophic prokaryotes and are increasingly applied to evaluate cyanobacterial community composition. The most widespread molecular methods for the study of aquatic microbiomes are denaturing gradient gel electrophoresis (DGGE) ( Shi et al, 2011 ; Li et al, 2012 ), terminal restriction fragment length polymorphism (T-RFLP) ( Chen et al, 2010 ; Li et al, 2011 ), Sanger sequencing of clone libraries ( Chen et al, 2010 ; Li et al, 2012 ; Cai and Kong, 2013 ), and more recently high-throughput sequencing ( Fortin et al, 2015 ; Zwirglmaier et al, 2015 ; Kurilkina et al, 2016 ; Lee et al, 2016 ; Berry et al, 2017 ).…”

Influence of cyanobacteria, mixotrophic flagellates, and virioplankton size fraction on transcription of microcystin synthesis genes in the toxic cyanobacterium Microcystis aeruginosa

“…The picocyanobacterium Synechococcus elongatus is of particular interest in this context because it is almost ubiquitously distributed (Stockner, Callieri, & Cronberg, 2002). The effect of Synechococcus on Microcystis gene expression is of ecological relevance since those cyanobacteria do not only co-occur (Fortin et al, 2015;Kolmonen, Sivonen, Rapala, & Haukka, 2004;Magana-Arachchi, Wanigatunge, & Liyanage, 2011;Ouellette, Handy, & Wilhelm, 2006;Zwart et al, 2005), but also can constitute the two most dominant cyanobacteria species in the phytoplankton community (Berry et al, 2016;Feng et al, 2016;Teneva, Mladenov, Belkinova, Dimitrova-Dyulgerova, & Dzhambazov, 2010;Ye et al, 2011).…”