A Portland State University marine biologist has received nearly $1.2 million from the National Science Foundation to investigate one of the ocean’s most important unanswered questions: who eats the planet’s most abundant photosynthetic organism?
Anne Thompson, an associate professor of biology at Portland State, won a five-year NSF Faculty Early Career Development, or CAREER, Award worth $1,165,130. Her research will focus on Prochlorococcus, a microscopic marine cyanobacterium that occupies a central position in the open-ocean ecosystem. Although scientists understand many of the conditions that allow this organism to grow, they know considerably less about the predators that consume it and the ecological consequences of that feeding.
Prochlorococcus is extraordinarily small, yet it is one of the most abundant photosynthetic cells on Earth. These cyanobacteria use sunlight to convert carbon dioxide and water into organic matter through photosynthesis, releasing oxygen as a byproduct. Distributed across vast regions of the sunlit ocean, they help drive global carbon cycling and support food webs that ultimately sustain larger organisms, from zooplankton to fish and marine mammals. Their sheer abundance means that even subtle changes in how they are consumed could influence the movement of carbon and energy through the sea.
Thompson’s project will examine how single-celled predators locate, capture and digest Prochlorococcus. The predator at the center of the research is a choanoflagellate, a free-living microorganism found throughout the oceans. Choanoflagellates are especially significant to evolutionary biologists because they resemble some of the closest single-celled relatives of animals. Their feeding behavior also offers a direct view of predation at a scale invisible to the naked eye.
A choanoflagellate captures prey by beating a whip-like structure called a flagellum. The movement creates a water current that draws surrounding particles and cells toward the predator. A ring, or collar, of fine finger-like projections then helps trap the prey before it is engulfed. Thompson’s laboratory has developed techniques to measure these encounters precisely, allowing researchers to determine which Prochlorococcus cells are captured and which manage to evade the predator.
During the five-year study, Thompson and her team plan to test approximately 40 types of Prochlorococcus. The experiments will explore whether choanoflagellates prefer particular strains and whether characteristics such as cell size, physiological condition or overall health influence the likelihood of being eaten. The researchers will also investigate whether Prochlorococcus can detect the presence of a predator and alter its behavior or physiology in response.
Such questions are difficult to answer in the natural ocean because predator and prey are mixed together in constantly changing conditions. In the laboratory, however, the two organisms can be grown under controlled conditions and observed in carefully designed experiments. By comparing different strains and environmental circumstances, the team hopes to identify the traits that make some Prochlorococcus cells more vulnerable than others. The results could clarify how microscopic interactions scale up to affect marine ecosystems and the global carbon cycle.
The award will also bring the research directly into Portland State’s undergraduate classrooms. Thompson plans to incorporate the experiments into two microbiology laboratory courses, giving roughly 200 students the opportunity to conduct real predation studies and contribute to the project’s data. Many of these students are preparing for careers in nursing, pharmacy and other health-related fields. Selected students will be able to join the laboratory for paid summer research and may continue into graduate study.
Thompson is also developing a popular-science book with Princeton University Press about Prochlorococcus and the process of scientific discovery. The project builds on equipment acquired through an earlier NSF award to Portland State, including a high-throughput flow cytometer capable of analyzing individual cells rapidly. She will obtain many of the Prochlorococcus strains used in the study from the laboratory of marine microbiologist Sallie “Penny” Chisholm at the Massachusetts Institute of Technology. By combining advanced single-cell analysis, controlled predator-prey experiments and student-led research, Thompson’s team aims to reveal how life at the smallest scale helps regulate the largest ecosystem on Earth.
Subject of Research: Marine microbiology, Prochlorococcus predation, ocean ecology and carbon cycling
Article Title: Portland State Biologist Wins $1.2 Million NSF Award to Study Who Eats the Ocean’s Most Abundant Photosynthetic Cell
Web References: Portland State University; NSF Award No. OCE-2543440
References: National Science Foundation Faculty Early Career Development (CAREER) Program; Portland State University; Sallie “Penny” Chisholm Laboratory, Massachusetts Institute of Technology
Image Credits: Portland State University
Keywords: Prochlorococcus, marine biology, ocean microbiology, choanoflagellates, predator-prey interactions, cyanobacteria, photosynthesis, carbon cycle, National Science Foundation, CAREER Award, Portland State University, marine ecology
