Author: Luís Sousa — Staff Writer
Date: July 30th, 2025
A microscopic marine organism discovered by a team of international scientists could become a major ally in the fight against climate change. Prorocentrum cf. balticum, a single-celled protist, has captured the attention of researchers due to its remarkable ability to trap carbon dioxide (CO₂) and transport it to the ocean depths, a process that helps offset atmospheric carbon levels. This organism, identified by researchers from universities in Sydney, Tasmania, and Edinburgh, is a mixotroph: it can photosynthesize like a plant or feed on other microorganisms like an animal. It thrives in a wide range of marine environments, from cooler to temperate waters, and plays a role in the ocean's biological carbon pump, a natural system that helps remove CO₂ from the atmosphere.
P. cf. balticum is part of the dinoflagellate group, featuring two flagella that allow it to move through the water. Measuring between 13 and 16 micrometers in diameter, this microorganism is capable of both asexual and sexual reproduction. Under nutrient-rich conditions, it reproduces asexually, while nutrient scarcity triggers sexual reproduction and increased feeding behavior.
It prefers to feed on smaller eukaryotic organisms, typically between 3 and 25 micrometers, such as diatoms, cryptophytes, and chlorophytes, although it cannot consume much larger organisms. Interestingly, it has also demonstrated the ability to feed on prokaryotes. Despite its flexibility, P. cf. balticum cannot survive solely on heterotrophy. In darkness, it cannot locate prey, highlighting its dependence on photosynthesis. This dual nutritional strategy, combining light-based carbon fixation and organic matter consumption, enables the protist to survive across varied ocean conditions.
The protist was first isolated in September 2018 from phytoplankton samples collected at an Australian research station. Even after a month without added nutrients, the cultures remained alive, indicating that mixotrophy played a role in their survival. Researchers used sterile techniques and controlled lighting to promote the growth of P. cf. balticum cultures, which were later analyzed genetically to confirm their identity.
Phylogenetic analysis based on DNA sequencing helped place P. cf. balticum within the tree of life, using common genetic markers to compare it with other dinoflagellates. Global data from the Tara Oceans expedition further revealed the protist's wide distribution, especially in waters where cells of its size (5–20 µm) are prevalent.
Traditionally, it was believed that marine microorganisms contribute to carbon sequestration only when they die and sink. However, P. cf. balticum appears to play an active role while still alive. It creates a unique structure called a mucosphere, a sticky, three-dimensional web made from mucous secretions. This structure traps prey and, once discarded by the protist, sinks, carrying organic carbon with it. These mucospheres, measuring up to 100 micrometers, act much like underwater spider webs. The protist builds one per day and typically discards it after consuming a single prey cell. Being negatively buoyant, the spheres drift downward, potentially reaching deep ocean layers and becoming part of the particulate organic carbon (POC) pool, essential for long-term carbon storage.
Light, Nutrients, and Prey: Triggers for the Mucosphere
Experiments have shown that light and prey availability are crucial for mucosphere production. After 8 hours of photosynthesis, P. cf. balticum begins to form the sphere. Without light or suitable prey, production slows or stops. In high-light conditions with eukaryotic prey, around 46% of the cells build mucospheres within 24 hours, compared to just 23% under low light. The presence of specific prey organisms also appears to trigger mucosphere formation. When organic phosphate runs low, the protist becomes more reliant on heterotrophy and increases its feeding behavior. Scientists observed a strong link between the presence of prey and the release of chemical signals that stimulate mucosphere creation.
Chemical analysis revealed that the spheres are rich in mucus-like compounds and may act as chemical lures. Using specialized tools (ISCA devices), researchers confirmed that prey are drawn to these structures by chemical attractants, further supporting the protist's active role in controlling its microenvironment.
A Promising Tool in Climate Mitigation?
The global urgency to reduce carbon emissions, as outlined in the Paris Agreement's 2050 target, has led scientists to explore nature-based solutions. The biological carbon pump (BCP), the ocean's natural method of sequestering carbon, is central to these efforts. Prorocentrum cf. balticum, through its daily production of mucospheres and its hybrid nutritional strategies, offers a promising new avenue for enhancing BCP efficiency. Unlike previous models that overlooked the importance of photosynthetic depth and particle size, recent approaches take into account the role of dynamic microbial communities like this protist.
As more is learned about the ecological function of this microorganism, its potential role in mitigating climate change becomes clearer. While still in the early stages of research, P. cf. balticum might one day be part of larger strategies to enhance oceanic carbon sequestration.
Sources: Based on experimental and genetic research conducted by scientists at the University of Sydney, University of Tasmania, and University of Edinburgh, including data from Tara Oceans and the GenBank database.