Elucidating the underpinnings of how algae respond to changing ocean conditions is essential to understanding food webs and the global carbon cycle. It also helps identify places where niche differentiation and competition might matter most. Field studies are essential for observing system change. Studies of physiology – using cultured algae that go down to the biochemical pathways and functions of genes— are important for developing a mechanistic understanding of responses. A first step is having reference information on the genes of environmentally-relevant algae, and, more broadly, of unicellular eukaryotes as a whole. We take several approaches to this, including whole genome sequencing (e.g. Worden et al. Science 2009) and transcriptome assemblies (e.g. Keeling et al. PLoS Biology 2014) for cultured taxa and targeted metagenomic assemblies (e.g., Cuvelier et al. PNAS 2010, Needham et al. PNAS 2019) for wild species.
Genomes tell you about possibilities, and from there, experimentation is needed to understand responses – whether at the RNA, protein or physiological level. A primary model organism in OEB is Micromonas (Fig. 1), a picoeukaryotic green alga for which we also have developed a genetic transformation system – at the same time we work with other algal groups to make sure we capture some of the diversity out there! Green algae like Micromonas belong to the Archaeplastida supergroup (Fig. 3) and provide insights into the evolution of land plants. We examine the evolution and function of photosensory proteins (e.g. Duanmu, Bachy et al. PNAS 2014) and perform research to discovery of novel functions and overall cell biological responses. We use advanced photobioreactors (as in the photo for this theme) and other systems simulate future ocean conditions allowing experiments that help identify proteins involved in algal responses and giving clues to evolutionary trajectories.
In addition to studying tiny photoautotrophic green algae like Micromonas, Bathycoccus (Fig. 2) and Ostreococcus – all of which are the products of primary endosymbiosis (Archaeplastids) we study algae from across the tree of eukaryotic life (Fig. 3), including haptophytes, rappemonads (which we discovered in collaboration with the Archibald (Dalhousie University) and Richards (University of Oxford) Labs, Kim, Harrison, Sudek et al. PNAS 2011), many stramenopiles and novel lineages. The stramenopile algae we study - and algae that also eat other cells (predatory mixotrophs) - provide sharply contrasting strategies to marine green algae. Cyanobacteria are never far from our thoughts but, for these, we work primarily with field samples to understand distributions among phytoplankton as a whole. This research is led by Alexandra Worden.
Other OEB research under this theme is led by Dr. Birte Matthiessen and more can be found at https://www.geomar.de/de/mitarbeiter/fb3/oeb/bmatthiessen/biodiversity/.