Unlocking the Ocean’s Microbial Secrets with Flow Cytometry

Flow cytometry is a powerful tool for revealing the structure of the phytoplankton community - the tiny but vital organisms that drive ocean productivity. By passing each particle through a focused laser beam in a stream of fluid (called the sheath flow), the instrument measures how cells scatter and absorb light. These optical signatures allow us to detect, identify, and quantify different groups of phytoplankton with remarkable precision.

The analysis requires only a few milliliters of seawater, which contains thousands of particles that can be detected and characterized. Onboard, a continuous pumping system draws in surface water, allowing real-time monitoring of phytoplankton abundance and distribution along the ship’s transect. We also collect CTD samples at different depths to study how these communities change throughout the water column, allowing comparisons between surface patterns, deeper layers, and other in-situ measurements.

Beyond mapping distributions, flow cytometry is also key to tracking the impact of experiments conducted at sea - such as nutrient incubations - by monitoring how phytoplankton communities respond over time. It’s like watching the ocean’s invisible life in action.

A cytogram showing the total sideward scatter over the total yellow fluorescence for each particle from a given sample

The flow cytometer used for sampling. Different groups can be distinguished by appropriate gating.

Aja and Felix doing some serious cytometry work.