Dissolved organic phosphorus use by the invasive freshwater diazotroph cyanobacterium, Cylindrospermopsis raciborskii

Abstract

This study examines the physiological responses of the diazotrophic cyanobacteria, Cylindrospermopsis raciborskii, to different dissolved organic phosphorus (DOP) compounds to explore mechanisms of environmental acclimation in this invasive species. Our results show that the specific growth rates of C. raciborskii cells in media treated with β-glycerol phosphate, d-glucose-6-phosphate, and (2-aminoethyl)-phosphinic acid were significantly higher than those of cells grown in phosphorus free media. We observed that maximal net photosynthesis was highest when cells were cultured with d-glucose-6-phosphate and lowest when cells were cultured with glyphosate. Similarly, rates of photosynthetic activity (maximum quantum yield, maximum electron transport rate, and photosynthetic efficiency) were observed to be highest in media treated with d-glucose-6-phosphate. We report that rates of alkaline phosphatase activity to the different organophosphates tested changed markedly in response to the concentration of dissolved inorganic phosphorus (DIP); a result supported by the amount of green fluorescent products revealed by ELF®97 phosphate dye (ELFP) and gene up-regulation for alkaline phosphatase (phoA). Our results indicate that C. raciborskii is able to use different organic phosphorus to support its growth when phosphorus is limited. In addition, we show that C. raciborskii has a higher availability to phosphate (COP) than phosphonate (CP). The results suggest that the strategic flexibility to environmental phosphorus might play an important role in the domination of C. raciborskii.