Cellular Response of Emiliania huxleyi to Growth on Phosphonates

Catherine Mahoney, Maine Maritime Academy, Corning School of Ocean Studies, Castine, ME, United States, Emily J McDermith, University of Rhode Island, Cell and Molecular Biology, Kingston, RI, United States, LeAnn Pritchard Whitney, Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States and Michael W Lomas, Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States
The importance of phosphorus (P) in cell structure and function make it an essential nutrient in the growth of phytoplankton. Large oceanic regions, such as the subtropical North Atlantic (NA), have growth-limiting levels of phosphate (Pi), the preferred form of P. In these regions, dissolved organic phosphorus (DOP) is an important alternative P source. The DOP pool largely consists of P-esters and phosphonates; both prokaryotic and eukaryotic organisms readily utilize P-esters, while phosphonates were thought to be an important P source only to prokaryotes. Recent studies have shown that some species of eukaryotic phytoplankton are able to utilize natural and/or chemically synthesized forms of phosphonates for growth, but the ability is not universal. In this study, we investigated the response of the eukaryotic phytoplankton, Emiliania huxleyi, to growth on methylphosphonate (MPN) as the sole source of P and compared to growth on replete and deplete levels of Pi . The effect of growth on MPN on cellular P and dissolved Pi concentrations were also measured. E. huxleyi supplemented with methylphosphonate achieved 5-fold higher growth rates and higher final cell concentrations than cells grown under P deplete conditions, while cells grown under replete Pi conditions achieved the greatest growth rate and cell concentrations. This suggests that E. huxleyi is able to utilize methylphosphonate to support growth. Cells grown on MPN treatments were found to reduce their cellular P content, whereas P deplete cells retained approximately 4 times more cellular P. This suggests that cells grown on MPN may use this P source to support production of new cells, while Pi deplete cells use available Pi for storage. This research enhances our understanding of the physiological effect of DOP utilization on eukaryotic phytoplankton. As climate change continues to affect nutrient availability, alternate sources of P, such as phosphonates, will become increasingly important.