Microplankton Study: Active Lipids Enable Smart Swimming Under Nutrient Limitation

Biophysicists at the University of Luxembourg have discovered how microplankton – key photosynthetic organisms that produce almost 50% of the oxygen we breathe – adopt a frugal lifestyle when nutrient intakes are restricted. They strategically use internal lipids to regulate swimming characteristics and maximize fitness.

Teacher. Anupam Sengupta and his team discovered this evolutionary trick by monitoring harmful bloom-forming phytoplankton species using quantitative multiscale imaging techniques, analytical and physiological measurements, fluid dynamic simulations and mathematical modelling.

Precise tracking of intracellular organelles (both size and position within cells) and swimming behavior reveal an emerging synergy between active lipid movement and cell shape, ultimately enabling microplankton to navigate dynamic nutrient landscapes. The groundbreaking findings appear in scientific advances.

Microbial nutrients are becoming scarce: an unavoidable consequence of climate change

As the open oceans continue to warm, altered currents and increased stratification will exacerbate nutrient limitation and thus limit primary production. The ability to migrate vertically offers motile phytoplankton a key – but energetically expensive – advantage, allowing vertical redistribution for growth, nutrient uptake, and energy storage in nutrient-poor waters.

In recent years, Prof. Sengupta has made groundbreaking discoveries pointing to exquisite biomechanical strategies that phytoplankton employ to adapt to changes in its habitat, such as those due to ocean turbulence (Nature 2017) and early warning protective mechanisms in the event of biophysical stress (Proceedings of the National Academy of Sciences 2021).

How these tiny but essential microbes adapt to changing nutrient landscapes, which are significantly influenced by climate change, is still unknown. Now, researchers from the Physics of Living Matter group, led by Prof. Sengupta, are unveiling the fate of phytoplankton through a multi-scale, interdisciplinary investigation involving microbiology, physics, mathematics and numerical modelling.

Based on a microplankton that forms red tides, the study uncovers how species use lipid droplets (LDs) – previously known as energy-storing organelles – as biomechanical triggers to regulate swimming characteristics in nutrient deprivation. By actively controlling the position and size of the LDs, cells can decide whether to swim up or down: an important survival property of photosynthetic microbes, since their vertical position in the water column determines light and nutrient availability.

Scale and multidisciplinary approaches were critical to the discovery

In addition to tracking and quantifying intracellular swimming characteristics with the custom-built Ocean-in-Lab setup, Prof. Sengupta’s team measured changes in the plankton’s ability to convert light into energy and the production of oxidative molecules, a key marker of physiological stress. Taken together, the results link intracellular reorganization to the biomechanics of swimming and further provide a mechanistic framework to estimate the underlying energetics of resource acquisition under supply constraints.

The combination of single-cell time-lapse imaging, particle image velocimetry of floating populations, numerical simulations and continuum modeling, and a variety of microbiological and analytical techniques were critical to this breakthrough discovery. This interdisciplinary research opens new perspectives in the study of active and intelligent microbial matter and offers a new perspective on microbial adaptation to environmental changes, including those caused by climate and lifestyle changes.