The role of nutrient availability on the production of cyanobacterial toxins
Isabela Diaz and Kimberly Hall
Cyanobacterial blooms are predicted to increase in the future as temperatures rise and water stratification increases. Dense cyanobacterial blooms can lead to anoxia in lakes, which can cause fish kills. Additionally, cyanobacteria produce a number of compounds, some of which are associated with an unpleasant taste or smell. More importantly, some cyanobacteria also produce toxic compounds. These toxins can contaminate drinking water and kill fish and wildlife. Microcystis aeruginosa, a bloom-forming cyanobacterium, produces a group of toxins called microcystins. Knowing the environmental conditions that are contributing to the production of toxins could give insight into prevention and mitigation of future algal blooms. However, previous studies have provided conflicting reports on the role of nutrients on toxin production. In this study, we investigated how nutrient availability affects the toxin production of M. aeruginosa. To investigate this question, cell density and microcystin production were measured for cultures grown under five different nutrient concentrations: control (standard BG-11 media), excess nitrogen (3x nitrogen concentration), limited nitrogen (1/3 nitrogen concentration), excess phosphorus (3x phosphorus concentration), and limited phosphorus (1/3 phosphorus concentration). We determined the cell concentration in each culture by doing visual cell counts using light microscopy. A microcystin-specific ELISA was used to determine the concentration of intracellular microcystins for each culture. We found that cultures grown with an excess of phosphorus reached a greater cell density than cultures grown at other nutrient concentrations. However, excess phosphorus cultures also produced a lower concentration of microcystin per cell than cultures grown under any of the other nutrient regimes. Microcystin concentration in the excess phosphorus treatment was significantly lower than either the excess or limited nitrogen cultures. Overall, we found that nutrient availability does affect both the M. aeruginosa cell concentration and production of microcystins. Blooms that occur with a higher concentration of phosphorus may be more dense but less toxic than those that occur under other nutrient conditions.
Isabela Diaz is majoring in biology with a minor in environmental science. She is the secretary of the Environmental Science Student Organization and a member of SAA. In the future she would like to pursue a career in marine biology.
Kimberly Hall is a graduating senior from Orangeburg majoring in biology-genetics and minoring in media & communication. She will pursue a Master’s in Public Health focused in epidemiology at MUSC beginning in fall. Kimberly served as a Presidential Ambassador, Vice President of Alpha Kappa Alpha, and Social Media Manager for the Environmental Science Student Organization.