Documenting shifts in diatom physiology across a natural nutrient gradient in the western North Atlantic

Diatoms, a group of unicellular phytoplankton, play a profoundly important role in marine primary production and carbon export. Though diatoms are most abundant in nutrient rich regions (e.g. upwelling regions, coastal margins) they also persist in low nutrient environments such as oceanic gyres. In the low nutrient ocean, it is thought that these persistent diatom communities serve as seed populations for locally important seasonal blooms. Though these blooms have been observed in the oligotrophic Sargasso Sea, little is known about the ecophysiology of western North Atlantic diatom communities. Here, we aim to gain insights into Sargasso Sea diatom nutrient physiology by using metatranscriptomic analyses to compare diatom community composition and gene expression patterns across the natural nutrient gradient between the Sargasso Sea, Gulf Stream and North Atlantic shelf. The taxonomic composition of the metatranscriptomes isolated from our study regions indicated that diatoms were present across the diverse environments sampled though the species present varied. Diatom nutrient physiology also shifted between regions with the expression of key nutrient assimilation, and nutrient responsive, transcripts varying between sites. This work provides insights into diatom strategies for coping with low nutrient environments in the Sargasso Sea and will lead to a deeper understanding of the diverse responses of in situ diatom communities to varied nutrient environments.