Diatoms response to salinity changes: investigations using single pulse and cross polarisation magic angle spinning

Area of Science:

• Marine biology
• Biogeochemistry
• Spectroscopy

Background:

• Diatoms are crucial marine phytoplankton that form silica shells (frustules).
• Salinity is a key environmental factor influencing diatom physiology and silica biomineralization.
• Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for analyzing silica structure.

Purpose of the Study:

• To investigate the impact of different salinities on diatom silica content and structure.
• To analyze silica condensation and organic matter presence using solid-state NMR.
• To compare single pulse (SP) and cross-polarisation (CP) MAS NMR techniques for diatom silica analysis.

Main Methods:

• Culturing of diatoms Thalassiosira pseudonana and Chaetoceros muelleri at 26, 36, and 46 PSU.
• Natural abundance 29Si magic angle spinning (MAS) NMR spectroscopy.
• Single pulse (SP) and cross-polarisation (CP) MAS NMR experiments, including variable contact time CP MAS for T. pseudonana.

Main Results:

• Diatoms cultured at salinities deviating from optimal (36 PSU) exhibited a less condensed silica state.
• Increased amounts of organic material were detected in diatoms cultured at non-optimal salinities.
• The presence of organic material affected the CP MAS NMR experiments, but its exact location (surface vs. frustule) was undetermined.

Conclusions:

• Salinity significantly influences diatom silica structure and composition.
• Non-optimal salinities induce changes in silica condensation and increase associated organic matter.
• Solid-state NMR techniques provide insights into diatom silica biomineralization under varying environmental conditions.