Function and Regulation of the Cyanotoxin, Microcystin

Wesley C. Jackson, Jr.^1,2 and Alan J. Lewitus^1,2,3

¹ Marine Biomedicine and Environmental Sciences Center, Medical University of South Carolina, Charleston, SC

² Hollings Marine Laboratory, Charleston, SC

³ University of South Carolina and South Carolina Department of Natural Resources, Charleston, SC

Microcystins are potent human liver toxins and carcinogens produced by cyanobacteria in freshwater to brackish environments.  The biochemical pathway that produces microcystins has been determined, but little is known about the regulation of this non-ribosomal pathway.  Active transport of microcystin out of the cyanobacterial cell does not appear to occur, suggesting an unknown internal function for this compound.  The highest concentrations of microcystin are found in the thylakoid, implying a role in photosynthesis.  This project tests two hypotheses related to the possible function of microcystin in photosynthesis: Hypothesis 1) microcystin participates in the regulation of photosynthesis through interaction with blue light receptor molecules in a melatonin-like circadian fashion; Hypothesis 2) microcystin plays a role in dissipation of excess energy produced through the photosynthetic process.  

To test these hypotheses, differences in genetic regulation and protein composition of two Microcystis aeruginosa cultures are being compared: a microcystin producer, UTEX 2385, and one that reportedly does not produce microcystin, UTEX 2386.  Microcystin concentrations will be determined in methanol extracts of these cultures, using High Performance Liquid Chromatography (HPLC) and Enzyme-Linked Immunosorbent Assay (ELISA).  To determine genetic differences in these Microcystis cultures, DNA will be extracted using the DNeasy extraction technique.  Real-time PCR will be used to sequence both cultures for genetic differences.  Finally, known autophosphorylating proteins regulated by full spectrum and blue light regulation (eg. phototropins) are to be determined using comparative Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS).  The results from this research will advance understanding of the physiological function of microcystin and the environmental conditions that promote its production.  This information is important to predicting cyanobacterial bloom toxicity, and could aid in bloom mitigation.