Katherine Helliwell: Molecular insights into abiotic and biotic factors shaping phytoplankton ecophysiology, signalling and evolution

Molecular insights into abiotic and biotic factors shaping phytoplankton ecophysiology, signalling and evolution

Marine phytoplankton contribute almost half of global primary production, and represent a critical sink for rising atmospheric CO2. It is therefore vital to better understand how key environmental factors control their growth and physiology. We have recently developed a new molecular tool kit, including genetically encoded fluorescent biosensors alongside CRISPR-Cas9 gene knockout techniques, to characterize the early signalling mechanisms enabling important phytoplankton taxa such as diatoms, to sense and respond to changes in their abiotic and biotic environment. Using this toolkit, we have identified that diatoms employ a novel Ca2+-dependent signalling pathway for sensing the critical macronutrient phosphorus. Moreover, our findings highlight that fundamental crosstalk between the essential nutrients P and N drive diatom recovery from P limitation. These mechanisms are likely critical to the success of diatoms in regions of episodic nutrient supply, and we are currently characterizing downstream components of the P-Ca2+ signalling pathway via functional gene characterization and phosphoproteomics approaches. Alongside abiotic controls, we are also exploring broader aspects of phytoplankton ecophysiology, including the role of biotic factors in shaping phytoplankton ecology and evolution. In particular, I will describe a new study employing environmental sampling methods to assess systematically the diversity and abundance of diatom algicidal bacteria in the Western English Channel. We have uncovered seasonal patterns of previously un-reported algicidal activity against diatoms in a diverse range of bacterial lineages. In addition, we have identified a facultative algicidal bacterium with a broad host range, which persists in the environment throughout seasonal cycles.