Cyanobacteria are photosynthetic prokaryotes found throughout the world in both aquatic and terrestrial environments. They are incredibly morphologically diverse and occur in both toxic and nontoxic variants. These bacteria are commonly referred to as “blue-green algae” and have been documented as the cause of numerous poisoning events throughout the years. As toxic bloom events continue to escalate it has become an increasing concern to better understand the growth factors involved in the life cycle progression and toxin production of these bacteria. This study focuses on three of the most prevalent cyanobacterial genera: Dolichospermum, Aphanizomenon, and Microcystis. Growth analyses on Dolichospermum (Anabaena) cylindrica and Aphanizomenon flos aqaue were conducted using various nitrogen and phosphorus concentrations representative of typical ranges on Lake Erie in the summer. The importance of these nutrients in life cycle progression was analyzed with both nutrient starvation and abundance scenarios. Cell count densities from the triplicated experiments (D. cylindrica) were averaged and their natural logs were plotted to produce the growth curves for each individual concentration and nutrient spiking. The maximum cell density across the nutrient spikes reached an upper limit in the low 108 cells/L range and a minimum in the mid- to high 107 cells/L range. Statistical analysis confirmed there was no significant difference in cell density between the various nutrient scenarios. In fact, cell density only significantly increased over time with each nutrient dosing, suggesting it is not a viable predictor of nutrient abundance. However, cell morphology and biovolume were extremely different across the various scenarios.
Aphanizomenon flos aqaue growth curves were done in only a single run (no replicates) due to laboratory shut down. However, development of a workflow using the 3D interactive Imaris software proved a very promising tool in quickly performing cell counts and statistical analyses while also noting and recording life cycle stage.