Why are the smallest organisms in the ocean some of the most powerful forces in nature? Human society, and indeed most life on Earth, relies on microscopic marine life forms for the air we breathe, the abundance of marine life, and the cycles of nutrients and energy that make the Earth life sustaining. Portland State University (PSU) research is illuminating who those tiny beings are, what they are like, and what secrets they may hold to the future of our planet.
Anne Thompson is an assistant professor of biology at PSU. She researches phytoplankton and their interactions with other microorganisms.
“Phytoplankton are the foundation that lets us derive nourishment from the sea, and they produce some of the oxygen we breathe. So they’re really important. The group of phytoplankton that my lab studies are really tiny cells—they’re called picocyanobacteria,” Thompson said.
These cells are the most abundant photosynthetic cells on the planet.
Thompson is the head of a laboratory called Microbial Ecology PDX, where she leads a research program aimed at investigating the roles microorganisms play in nutrient cycling, symbiosis, and ecosystem resilience – and is devoted to training students, teachers, and the public in the wonder and power of microbial life in the oceans
From the open ocean to the Microbial Ecology lab
The Microbial Ecology Lab contributes critical insights to our basic understanding of life, which could lead to long-term applications in environmental stewardship, climate resilience, and biotechnological innovation.
A Precursor to Plant Life
Cyanobacteria, a subset of the larger group of phytoplankton, are a diverse lineage of organisms. Often called blue-green algae, some forms of cyanobacteria are toxic—like the ones responsible for heat-driven cyanobacterial blooms that are a safety concern for humans and pets in Portland, and throughout Oregon, during summer and early fall. The picocyanobacteria studied in Thompson’s lab are not known to be toxic, but are of great interest to researchers.
“The lineage as a whole is incredible, because it’s been around on Earth for billions of years—these are the cells that invented the production of oxygen through photosynthesis,” Thompson said. “They will be here long after we’re gone, too.”
The reason for their resilience and longevity? They don’t depend on other life in the same way we do. Instead, they derive energy from sunlight and carbon dioxide. From this they create oxygen, some can fix nitrogen, and in doing so they support entire food chains.
Predator-Prey Relationships
“The thing we’re working on now is figuring out who eats these cells. We know that they are killed by viruses. And we know that they’re eaten by single-celled organisms called protists. But we don’t know what those exact interactions are,” Thompson said.
Are the picocyanobacteria passive prey, helpless against the approach of a hungry protist? Or do they actively try to evade predators? What defense mechanisms, if any, might they have? And a crucial question: What happens to them after they’ve been eaten? Where does that organic material end up?
That last question is important to our understanding of climate science. The level of carbon in the atmosphere is a key factor influencing Earth’s climate, and the picocyanobacteria take carbon dioxide from the atmosphere. Once they are killed, does the carbon contained in their bodies get released back into the atmosphere, or does it sink to the bottom of the ocean and get buried?
Knowing more about their predators could answer this. If they get engulfed by a larger microorganism with a big fecal pellet that sinks fast, then the carbon from the phytoplankton likely gets exported—sequestered to the bottom of the sea. If they get eaten by something smaller, which does what is called sloppy feeding—taking small bites and basically making a mess—then the dissolved organic material gets recycled into the ocean, where it can easily be passed back to the atmosphere.
“If we can answer some of these questions, we hope that we’ll understand phytoplankton better, and then we’ll be able to better predict how phytoplankton can support important economies, important ecosystems, and really, the habitability of the earth,” Thompson said.
Lifelong Learning
In Thompson’s lab, there is a light incubator set to a sunrise/sunset cycle. Inside of it, a vast population of phytoplankton live, reproduce, and die. Outside of it, a group of people at all stages of their scientific careers learn from the phytoplankton and each other – training the public, students, and teachers is an important aspect of Thompson’s lab mission.
Working with teachers is one particular area of focus for Thompson. Through the M.J. Murdock Charitable Trust Partners in Science program, Thompson has hosted several STEM high school teachers in the lab where they developed their own project on phytoplankton in the open ocean and response to plastics. This formative collaboration supported by the Trust led Thompson to seek additional opportunities to support teacher education. Through NSF funding, Thompson and collaborators Claudia Ludwig and Nitin Baliga worked with eight high school STEM teachers, over the course of three summers, to translate research on picocyanobacteria into the high school curriculum. The module they created – called “Our Invisible Forest: What’s in a Drop of Seawater”, engages students in ocean science, chemistry, physics and biology – all around the idea that the ocean is teeming with microbial life.
“In addition to my work with teachers, I have a steady flow of PSU students through my lab. Currently, I have one graduate research assistant—a masters student,” Thompson said. “And then this summer I have added an undergraduate student as well, and that’s fantastic. Then I have a high school student in the lab, too. And I also have a postdoc and a research adjunct faculty member. So I have a huge range of career levels in the lab right now.” This multi-level environment benefits everyone involved—early-career students gain exposure to advanced research, while more experienced researchers sharpen their mentorship skills.
Given the urgency of our climate crisis, this is an important moment for learning more about some of earth’s key players. Picocyanobacteria love the warm, nutrient-poor open ocean. Those areas of the planet are expanding now, and will continue to expand in the years to come. As the ocean continues to change, it is likely that the picocyanobacteria will thrive. Other types of phytoplankton may not be so lucky—some live in cooler waters and need more nutrients. Many are important to coastal fisheries and human food sources. So humans have much to gain from having a better understanding of these tiny life forms and their ecological interactions.
“It’s a value to our society to understand how life works. And these incredible cells are simple. They live and die. They’ve been doing it for millions of years – and their ancestors have been doing so for billions of years! And if we can understand the secrets of how they live and persist in changing conditions, we can learn more about life itself, which has untold and immeasurable value to humans,” Thompson said.
Research with public impact is one of PSU’s top priorities. Annie Lindgren, PSU’s Associate Vice President of Research, works to advance PSU’s interdisciplinary research initiatives and build partnerships with industry and other community stakeholders.
“Dr. Thompson’s track record of funding tells a powerful story of impact in terms of both research and education. Anne recently received an Early Career Simons Foundation Award, which is a testament to her standing among the world’s most promising researchers. But it’s the early opportunities provided by M.J. Murdock Charitable Trust, and successive grants from the National Science Foundation, that truly underscore her ability to build a research program that consistently shapes new directions in microbial ecology and provides educational opportunities to learners of all ages. This has an impact far beyond the lab, and it’s why so many increasingly look to her for insight and innovation,” Lindgren said.
