# Investigation of Methionine Metabolism in Coccolithophore by In Situ Light-Coupled Nuclear Magnetic Resonance Spectroscopy

## TL;DR

This study uses a new NMR method to track methionine metabolism in coccolithophores under different environmental conditions, revealing how stress affects sulfur-related processes.

## Contribution

A novel in situ light-coupled NMR setup is introduced to directly monitor methionine metabolism in coccolithophores under varying environmental conditions.

## Key findings

- Coccolithophores convert methionine into MTOB, which is secreted, while DMSP remains intracellular.
- Elevated temperatures and darkness increase methionine consumption but reduce its conversion into MTOB and protein incorporation.
- Seawater acidification has minimal impact on methionine metabolism in coccolithophores.

## Abstract

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 in situ light-coupled nuclear
magnetic resonance (NMR) spectroscopy setup to monitor methionine
metabolism directly in coccolithophore cultures under varying environmental
conditions. Combining in situ 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.