Phytoplankton are the major photosynthetic organisms in aquatic environments that play a critical role in the global carbon cycle as well as the biogeochemical cycling of many other elements. They are the base of the marine food web, and thus are intricately linked to marine fisheries and ocean productivity. Despite being classified as autotrophic, most phytoplankton depend on closely associated bacteria that provide them with essential metabolites and cofactors required for their survival and adaptation to the changing environment. In exchange, phytoplankton provide these bacterial microbiomes with dissolved organic matter (DOM) that attracts and nurtures these algal microbiomes. Exchanges between phytoplankton cells and their microbiome occur in a small region that surrounds algal cells called the phycosphere. Exchanges of metabolites in the phycosphere is believed to influence major phenomena in the oceans, including primary productivity, harmful algal blooms, carbon export and cloud formation. Despite the importance of these relationships, studying the phycosphere and the organisms interacting within it is a major challenge given its small size (picoliter to nanoliter in volume) that renders studying these interactions at a relevant scale challenging. In addition, the high diversity of microbes in the ocean hinders our ability to study these relationships by simply sampling the ocean using traditional techniques. To address these challenges, our lab (1) uses model systems to study symbiosis between major phytoplankton lineages (namely diatoms and dinoflagellates) and their microbiome, (2) develops cutting-edge techniques to sample the phycosphere using novel microfluidic approaches, (3) innovates methods in single-cell genomics and ultra-high resolution mass spectrometry to characterize and quantify new symbiotic relations in the phycosphere. Our ultimate goal is to make these developments and knowledge more accessible and to integrate new knowledge into ocean models to better predict the effects of climate change on these critical symbiotic interactions.
Phycosphere colonization by Roseobacters
Roseobacters are among the most abundant and ecologically important group of bacteria in marine environments. They are also prominent members of the phycospheres of many phytoplankton lineages, including diatoms, dinoflagellates and coccolithophores. We aim to characterize the mechanisms that enable these bacteria to colonize diatom phycospheres and gain an advantage over other bacteria.
Plain English Summary
Like plants on land, phytoplankton are the primary photosynthetic organisms in marine and fresh water. These microbes are responsible for ≥ 50% of all Earth's photosynthesis and oxygen. They play a major role in removing carbon dioxide from our atmosphere and sustain fisheries throughout the oceans; however, disturbances to our oceans can cause these relations to lead to a reduction in fisheries or the development of red tides (aka harmful algal blooms). These algae do not live in isolation but are surrounded by a microbiome of bacteria that sustain their growth and survival. This relationship is based on exchanging important molecules, like sugars for energy production, amino acids for cellular growth and vitamins just to name a few, that collectively support the growth of both phytoplankton and their microbiome. These critical exchanges happen in a microscopic area surrounding algal cells, called the phycosphere. To observe these phycosphere interactions directly, highly sophisticated methods are needed to overcome the fact that the phycosphere is extremely tiny. To solve this problem, we use model systems in the lab to study those interactions, we are developing novel methods in microfluidics to pick out a single algal phycosphere (the Phycopick) from its surroundings, and finally we are innovating methods to detect and identify the microbes and molecules exchanged by phytoplankton and their microbiome from this tiny phycosphere sample. Identifying these symbiotic exchanges between phytoplankton and bacteria will enable us to understand and better predict how climate change will influence these organisms that play critical roles in sustaining life in the oceans.