Recent Student Publications
Investigation of the algicidal exudate produced by Shewanella sp. IRI-160 and its effect on dinoflagellates
Kaytee L. Pokrzywinski, Allen R. Place, Mark E. Warner and Kathryn J. Coyne
Published in Harmful Algae, September, 2012, volume 19, pages 23-29.
The bacterium, Shewanella sp. IRI-160, was previously shown to have negative effects on the growth of dinoflagellates, while having no negative effects on other classes of phytoplankton tested. In this study, we investigated the mode of algicidal activity for Shewanella sp. IRI-160 and found that the bacterium secretes a bioactive compound. The optimum temperature for production of the algicidal compound by this bacterium was at 30 °C. Bacteria-free filtrate of medium containing the algicide (designated IRI-160AA) was stable at temperatures ranging from −80 °C to 121 °C, and could be stored at room temperature for at least three weeks with no loss in activity. Algicidal activity was eluted in the aqueous portion after C18 extraction, suggesting that the active compound is likely polar and water-soluble. The activity of IRI-160AA was examined on a broad range of dinoflagellates (Karlodinium veneficum, Karenia brevis, Gyrodinium instriatum, Cochlodinium polykrikoides, Heterocapsa triquetra, Prorocentrum minimum,Alexandrium tamarense and Oxyrrhis marina) and three species from other classes of algae as controls (Dunaliella tertiolecta, Rhodomonas sp. and Thalassiosira pseudonana). Algicidal activity was observed for each dinoflagellate and little to no negative effect was observed on chlorophyte and cryptophyte cultures, while a slight (non-significant) stimulatory effect was observed on the diatom culture exposed to the algicide. Finally, the effect of the algicide at different growth stages was investigated for K. veneficum and G. instriatum. IRI-160AA exhibited a significantly greater effect during logarithmic growth compared to stationary phase, suggesting a potential application of the algicide for prevention and control of harmful dinoflagellate blooms in the future.
Effects of growth phase, diel cycle and macronutrient stress on the quantification of Heterosigma akashiwo using qPCR and SHA
Christopher R. Main, Cameron Doll, Colleen Bianco, Dianne I. Greenfield, and Kathryn J. Coyne
Published in Harmful Algae, Volume 37, Pages 92-99
The development of molecular probe technologies over the last several decades has enabled more rapid and specific identification and enumeration of phytoplankton species compared to traditional technologies, such as light microscopy. Direct comparisons of these methods with respect to physiological status, however, are sparse. Here we directly compare quantitative real-time PCR (qPCR) and sandwich hybridization assay (SHA) for enumerating the raphidophyte Heterosigma akashiwo at several points during its growth phase, over a diel cycle and with macronutrient stress in laboratory cultures. To ensure consistency between comparisons, a single cellular homogenate was generated from each culture and split for analysis by qPCR and SHA. Since the homogenate was generated from the same number of cells during each experiment, results reflect changes in nucleic acid content (rRNA and DNA) at each time point or in response to environmental conditions relative to a reference sample. Results show a greater level of precision in SHA results which contributed to significant (2–3 fold) differences in rRNA content per cell in several of these analyses. There was significantly greater rRNA content during lag and exponential phases compared to stationary phase cultures, and a significant decrease in rRNA content during the light cycle compared to cells harvested in the dark. In contrast, there were no significant differences in DNA content per cell as determined by qPCR over a diel cycle or during different growth phases. There was also no decrease in either rRNA or DNA content for cultures under low P conditions compared to nutrient replete conditions. However, both rRNA and DNA content were significantly lower under N stress when compared to nutrient replete conditions. Results of this study suggest that growth stage, nutrient stress and cell cycle may impact molecular analyses, and that physiological status should be taken into account when using these methods for HAB monitoring.