Investigating Picocyanobacteria – a closer look

This blog series is devoted to a deeper understanding of the research going on around us. This week, we’ll learn about Hanna, Javi and Soran’s work at the K-Station on picocyanobacterial dynamics and nutrient response in the Baltic Sea.

Every Tuesday, rain, snow or shine, members of “Team Pico” head out bright and early to the new K-Station, situated at the open-air bathhouse located just across from Kalmar Castle. There, they submerge water samplers to 1 m depth to measure a suite of different parameters. One morning this spring, against a chorus of very noisy gulls across the bay, Hanna and Javi discuss the work they’ve been doing in this FORMAS project.

The aim of this project is to assess abundance, seasonal dynamics, and carbon fixation activity of the picocyanobacterium Synechococcus in a dynamic coastal ecosystem, information that will be crucial when predicting how picocyanobacteria will respond to climate change. The project is within the EcoCHANGE -Ecosystem dynamics in the Baltic Sea in a changing climate framework with Catherine Legrand as vice coordinator and theme leader.

IMG_5424Picocyanobacteria are tiny photosynthetic bacteria that are ubiquitous in aquatic ecosystems and significant contributors to global primary production. These tiny CO2 fixers are at the base of the marine food chain, yet our knowledge about them and their community dynamics in the Baltic Sea is relatively little. While methodically winding the cord of one of her sampling instruments, Hanna discusses how the techniques for studying these bacteria must be adapted for their tiny size:

“By just looking at them under the microscope we can’t identify what the species are so we really need molecular techniques to complement those analyses. We use a number of different ways to look at the picocyanobacteria – to find out how many they are, how they vary during the season, and who they are.”


Since the project began, “Team Pico” has grown. Javi Alegria, a PhD student supervised by Catherine Legrand joined us from Spain in February, and Soran Mahmoudi, a field assistant joined us during the summer.

The field and lab work has already revealed some interesting findings. Says Javi, “The biomass, composition of cell size and their pigments are different for different seasons,” indicating that these tiny bacteria are responding to seasonal changes.

With their jugs of sampled water in hand, “Team Pico” head back to the lab and don their white coats for filtering, cataloguing and fun!

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Lab work is comprised of using a variety of filters with different characteristics depending on the information we want to get from the marine community. One of the first filters Javi uses is to separate the small picoplankton community from bigger phytoplankton. Then he will measure the primary production (carbon fixation) of the entire community and compare it with the picoplankton community.

Hanna continues: “Right now we don’t know how much the picos contribute to carbon fixation in the Baltic Sea. People may think, ‘oh, they’re so small, they’re not really making a difference.’ But even if you’re little, if there’s many of you, it could be that you’re making a huge difference. So that’s what we’re trying to investigate.”

In addition to abundance and productivity, “Team Pico” is looking at nutrient response and community composition by doing manipulation experiments in the lab.

Have a look at the photos below to learn more about “Team Pico’s” lab work and what they’re investigating.

Above: Vacuum pumps are used to pull seawater through filters, which are then analyzed for chlorophyll a, a measure of phytoplankton biomass or saved for DNA analyses.

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Shake it up!: “Before you take a sample you always have to shake the bottle to make sure that the sample is mixed”
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Hanna uses the pipette to take samples for flow cytometry, a method used to count very small cells.


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Javi filters water to determine nutrient concentrations.

This summer, Javi presented the first of their findings at the ISME conference in Leipzig, Germany, which compared picocyanobacterial dynamics and nutrient response at the K-Station versus offshore at the Linnaeus Microbial Observatory a time-series program that has been running since 2011.

Thanks “Team Pico” for opening their world to us, and bringing us on the journey of investigating the tiny bacteria that play such an important role in the sea. Stay tuned for future updates on this project!

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