Masters Defense

Exploration of Cyanobacterial Diversity Across the Laurentian Great Lakes, with Emphasis on the Enigmatic Cyanobium Genus

Cyanobacteria are integral to the phytoplankton community and help drive productivity in all waters. Across the Laurentian Great Lakes (LGL), cyanobacteria are important phytoplankton members and integral to food webs. However, much of the research on cyanobacteria has focused on the central roles of bloom-forming genera such as Microcystis and Dolichospermum. Given the importance of cyanobacteria to these systems,  a broader view of the total cyanobacterial diversity and linkages between lakes across the LGL can provide important insight into water column productivity and how the geochemistry of the lakes may influence these important primary producers. As part of the Great Lakes Biology Monitoring Program’s (GLBMP) Cooperative Scientific Monitoring Initiative (CSMI), metagenomic samples were collected between 2016 and 2020, at two-time points in each LGL, with the exception of Lake Michigan. Analysis of metagenomic sequencing libraries revealed that cyanobacterial communities were dominated by picocyanobacteria in all five Great Lakes. Additionally, cell counts indicate that picocyanobacteria have increased in abundance over the last 10 years. To date, little work has focused on these important microorganisms, not just in the LGL but globally. Thus, to better understand picocyanobacterial dominance, we explored the spatial abundance patterns and metabolic capabilities of one dominant picocyanobacterial genus, Cyanobium. Using a combination of our sequenced genomes and publicly available genomes, I compiled a total of 166  LGL genomes for analyses. Phylogenomic analyses show that multiple Cyanobium species occur in each lake, with fifteen different phylogenetic clades in Lake Erie alone. While many of the genomes shared similar metabolic capabilities, we also detected a diverse suite of nutrient- and carbon-acquisition genes that differed by lake, which partially explains their dominance across the wide trophic gradient of the LGL. This work highlights the importance of this ubiquitous genus and lays the foundation for future LGL studies that quantify shifts in the cyanobacterial community in a changing climate.