New findings reveal the adaptive capacity of pennate diatoms in oceanic environments

A recent study involving researchers from the Institut Mediterrani d'Estudis Avançats (IMEDEA, CSIC-UIB) has expanded our understanding of phytoplankton, especially diatoms. This study has revealed that these cells are not mere passive particles, but dynamic entities capable of actively adapting to their environment. Researchers have discovered that the shape and size of diatoms play a crucial role in their ecology and adaptive capacity, enabling cell-to-cell communication and facilitating complex ecological processes.

Diatoms are typically classified into two subclasses: centric diatoms, characterized by radial symmetry, and pennate diatoms, which exhibit bilateral symmetry. These groups show distinct habitat preferences, with centric diatoms dominating pelagic environments and pennate diatoms thriving in benthic habitats. However, certain species of pennate diatoms, such as those in the genus Pseudo-nitzschia, have successfully adapted to pelagic environments, overcoming challenges such as staying within the illuminated layer of the ocean (photic layer).

Staying within the photic layer and optimizing light absorption represents a significant challenge for these planktonic pennate diatoms, as they lack adaptations to actively regulate buoyancy, which they have in centric diatoms. The researchers studied the evolutionary adaptations that allow these diatoms to meet this formidable challenge. This research provided precise measurements of the sinking dynamics of pennate diatoms and explored their microscale biophysical interactions with environmental factors.

This group of diatoms usually forms chains with flexible connections between cells, which allows them to change the orientation of the chain during sinking. The researchers found that regardless of the initial orientation of the chain, it always ends up acquiring a stable horizontal orientation. This transition from a vertical orientation (typical of individual cells) to a horizontal one has profound implications for light exposure and sink rates. These findings highlight the ecological importance of these processes in the life cycle of pennate diatoms. This study emphasizes that cell shape and size play a more significant role in phytoplankton ecology than previously recognized.

In addition, this study extends the finding of the observation of the phenomenon of intercellular communication by fluorescence light, recently described in the species Pseudo-nitzschia delicatessima (Font-Muñoz et al 2021), to two other species: Pseudo-nitzschia pungens and Pseudo-nitzschia fraudulenta. This study highlights the complexity and sophistication of phytoplankton cells, which possess advanced mechanisms to adapt and thrive in diverse environmental conditions, challenging the traditional view of these cells as passive particles.

Sourisseau, M., Font‐Muñoz, J., Bellouche, S., Fauvarque, O., Rouxel, J., Tardivel, M., & Sauvey, A. (2024). Sinking rates, orientation, and behavior of pennate diatoms. Journal of Phycology.

Font-Muñoz, J. S., Sourisseau, M., Cohen-Sánchez, A., Tuval, I., & Basterretxea, G. (2021). Pelagic diatoms communicate through synchronized beacon natural fluorescence signaling. Science Advances, 7(51), eabj5230.