Investigation of Methionine Metabolism in Coccolithophore by <i>In Situ</i> Light-Coupled Nuclear Magnetic Resonance Spectroscopy

Coccolithophores play critical roles in global carbon and sulfur cycles. They contribute to the carbon cycle through photosynthesis and calcification and the sulfur cycle by producing dimethylsulfoniopropionate (DMSP). Despite their ecological importance, the details and dynamics of methionine metabolism in coccolithophores are poorly understood. Here, we introduce an <i>in situ</i> light-coupled nuclear magnetic resonance (NMR) spectroscopy setup to monitor methionine metabolism directly in coccolithophore cultures under varying environmental conditions. Combining <i>in situ</i> light-coupled NMR spectroscopy and ¹³C magic angle spinning (MAS) spectroscopy, we observed that coccolithophores can take up methionine and convert it into 4-methylthio-2-oxobutyrate (MTOB), which is subsequently secreted into the culture medium, while DMSP was detected only intracellularly. Furthermore, environmental factors, such as elevated temperatures at 24.8 °C, which is 6.8 °C higher than the typical growth temperature for coccolithophores, and darkness, accelerated methionine consumption but reduced its incorporation into proteins and its conversion into MTOB, suggesting a shift toward alternative metabolic pathways under stress. In contrast, seawater acidification had minimal effects on the methionine metabolism. These findings provide new insights into how environmental conditions influence sulfur metabolism in coccolithophores, with potential consequences for their ecological functioning under future climate scenarios.