MSc Exit Seminar – Rosemary Saati (Fulthorpe lab)

MSc Exit Seminar

Friday September 16^th, 11:10 am – Room SW 403, University of Toronto at Scarborough

Rosemary Saati (Fulthorpe lab)

“Characterization of the Cyanobacterial Harmful Algal Bloom Community in Hamilton Harbour, Lake Ontario“

Abstract

Despite management efforts to decrease exogenous phosphorus loadings since the 1970’s into Hamilton Harbour, the bay has seen a reappearance of Cyanobacterial harmful algal blooms (CyanoHABs) often dominated by the notorious colonial toxin producer Microcystis and other filamentous bloom-forming genera. Studies on CyanoHAB communities in freshwater systems have concentrated on Cyanobacterial species composition and the physico-chemical factors influencing their growth in culture experiments. Little is known about the interspecific relationships between Cyanobacteria, heterotrophic species and the impact on natural grazer dynamics mainly since most aquatic species are non-culturable in the laboratory. Culture-independent methods have recently revealed that heterotrophs are abundant and diverse in freshwater although their interactions with Cyanobacteria throughout blooms remain unknown. I applied these methods to elucidate the epilimnetic community composition throughout the summers of 2014 and 2015. Correlations were determined between community structure determined by Terminal Restriction Length Polymorphism (T-RFLP) of community 16S and 18S rRNA genes to the physico-chemical parameters collected on site. The most influential factors on community structure in 2014 were chloride and sulfate concentration whereas nitrate/nitrite and ammonium had a stronger influence on the 2015 community. Community composition associated with these blooms was investigated using 454-pyrosequencing and shotgun metagenomics. Taxonomy assignment revealed a predominance of Actinobacteria and Proteobacteria in June/July samples. The Actinobacteria:Cyanobacteria ratio decreased both summers with Planctomycetes  emerging during Cyanobacteria predominance in August/September. Analysis of eukaryotic ribosomal genes revealed a diversity of Metazoa, Chlorophyta, and SAR group including a novel Rhizaria in 2014 but shotgun data from the 2015 samples suggested eukaryotes encompassed a significantly smaller of the total community compared to bacteria. Nitrate/nitrite uptake and intracellular reduction by Cyanobacteria and Betaproteobacteria as well as Cyanobacterial nitrogen fixation genes increased throughout the summer suggesting that microorganisms that could take advantage of ammonium limitation in August and September predominated. These results provide the first characterization of the overall CyanoHAB community in Hamilton Harbour as well as a reference point for future studies on this system and other similar systems. They further provide new insights for future management into which environmental factors are likely shaping this specific community throughout the summer.