Where’s the P in Plankton? Phosphorus Allocation to DNA across Diverse Marine Picoplankton

Phosphorus (P) is a critical nutrient for survival, particularly in oligotrophic environments such as the Sargasso Sea. Microbes require phosphorus to build and maintain cellular components, including DNA, RNA, and lipids. We expect variation across microbes in the fraction of cellular P allocated to each of these components. We hypothesized that a high but variable percentage of cellular P will be allocated towards DNA. Studying cellular P allocation can offer insight into the role of different microbes in phosphorus cycling in low-P regions like the Sargasso Sea. To assess allocation of P to DNA, we first tested the efficiency of different DNA extraction methods and then analyzed the amount of extracted DNA from different microbial groups. We performed DNA extractions using four different extraction kits and determined Promega Reliaprep Blood gDNA Miniprep System to be the most efficient. We extracted DNA from cultured picoplankton which are representative of the most abundant species in the Sargasso Sea: Synechococcus (WH8102), Prochlorococcus (MED4 and MIT9301), and heterotrophic bacteria (HTCC2516 and HTCC2601). We found that the percentage of P allocated towards DNA varies across microbial species and across strains within the same genera. Additionally, we estimated the relative number of copies of the genome per cell, and found that more copies of the genome per cell, not necessarily a larger genome size, may correlate with allocating a larger percentage of cellular P towards DNA. By understanding how phosphorus cycling works on the molecular level in different species of picoplankton, we can develop a greater understanding of the role of these picoplankton in phosphorus cycling as a whole in the Sargasso Sea.