A transcriptome-enabled study of nutrient and CO2 responses for three harmful algae

Sonya Dyhrman, Biology


Project summary

Coastal nutrient inputs drive phytoplankton growth, which is largely beneficial, but in some cases nutrients, metals, and even vitamins in the water can induce the growth of harmful species over beneficial species resulting in a harmful algal bloom (HAB).  Dinoflagellate and raphidophyte phytoplankton cause harmful algal blooms (HAB) in coastal U.S. waters with serious detriment to ecosystem services, aquaculture, and public health. Many of these blooms are related to nutrient availability, particularly in coastal and estuarine settings. Recent work also indicates that members of these phytoplankton groups will grow faster with the increased CO2, and temperatures predicted in many coastal environments. This may further exacerbate bloom formation and their impacts in the future ocean. Despite decades of study, the ability to predict how nutrients and CO2 influence the growth of different coastal HAB forming phytoplankton species is still limited because we often lack even a basic understanding of the molecular pathways these species use to acquire these resources. Recent advances in DNA/RNA sequencing now make it possible to study the cellular physiology and response of HAB species to nutrient availability with unprecedented resolution – providing a unique window into the capacity of these organisms to acquire nutrients, and the physiological costs and tradeoffs associated with different strategies under conditions of variable nutrient and CO2 supply. Here I propose a transcriptome-enabled study of the nutrient and CO2 responses for three HAB species that form dense, nearly monospecific, blooms in coastal and brackish systems with highly variable environments; the dinoflagellates, Prorocentrum minimum and Alexandrium monilatum, and the raphidophyte, Heterosigma akashiwo. The purpose of comparing these three organisms is to determine whether they share common strategies in their nutritional physiology that contribute to their success at bloom formation.

This is an exciting time in marine microbiology and the field is poised for rapid advances with changes in RNA sequencing that allow uniquely comprehensive resolution of the activities of harmful algae and their nutrient acquisition pathways. It is the ordered expression of genes, into RNA (RNA = the transcriptome), which controls the cellular functioning of these organisms.
As such, the transcriptome profile of an organism, and how it changes in different conditions, can provide a comprehensive view of how HAB organisms respond to changes in nutrients such as N and P, and elevated CO2 predicted in a future ocean. Growing the three test species under low N, low P, nutrient replete, and high CO2, we will sequence the RNA present in each condition. From these experimental treatments we will 1) identify the genes that are expressed, or “turned on”, 2) quantify the number of each expressed gene across the different treatments, and 3) assay a variety of physiological parameters to track potential physiological costs associated with changes in N, P, and CO2 supply. These proposed objectives relate directly to COI priority research themes; 1) natural and anthropogenic threats to the coastal environment including harmful algal blooms, and 2) coastal carbon cycling/acidification. Although I have extensive experience with studies of HAB nutritional physiology and sequenced-based transcriptome profiling, I do not have much experience working with carbon metabolism or ocean acidification related research.  As such, the proposed work would provide valuable proof of concept for a new set of federal research proposals in this area.