.jpg) |
| Photo Credit: Jo Sorgenfri |
Scientific Frontline: Extended "At a Glance" Summary: Acetone Carboxylation in Arctic Ocean Bacteria
The Core Concept: A newly discovered Arctic Ocean bacterium, Porticoccus arcticus, utilizes a rare metabolic pathway called acetone carboxylation to consume acetone and convert atmospheric carbon dioxide into essential cellular building blocks.
Key Distinction/Mechanism: Unlike typical marine organisms, Porticoccus arcticus relies on photoheterotrophy, combining the animal-like consumption of organic carbon (acetone) with the plant-like fixation of inorganic carbon (carbon dioxide), all while using sunlight as an energy source.
Origin/History: Researchers from Concordia University discovered this metabolic anomaly by analyzing the genomic composition of bacteria residing in the frigid waters of the Beaufort Sea.
Major Frameworks/Components:
- Acetone carboxylation: A specific metabolic pathway that converts acetone and carbon dioxide into compounds for central cellular metabolism.
- Photoheterotrophy: The biological capacity to utilize light as an energy source while simultaneously consuming organic carbon.
- Proteorhodopsins: Light-sensitive proteins encoded by the bacterium's genome that facilitate the capture of solar energy.
- Genomic reconstruction: The use of genetic sequencing to map an organism's unexpected energy and carbon metabolic behaviors.
Branches of Science: Marine Microbiology, Molecular Genetics, Microbial Ecology, Biogeochemistry, and Genomics.
Future Application: Insights into this unique metabolic pathway can improve climate models by revealing how marine ecosystems process carbon, potentially spurring investigations into similar carbon-capturing mechanisms in freshwater, coastal, and open-ocean environments.
Why It Matters: As the Arctic Ocean rapidly warms and sea-ice conditions shift, understanding how foundational microorganisms capture atmospheric carbon and adapt to resource-scarce waters is critical for predicting broader ecological changes, carbon cycles, and marine ecosystems in vulnerable regions.
.jpg) |
| David Walsh: “The genomic composition of these organisms led us to predict the different types of energy and carbon metabolism that exist.” Photo Credit: Courtesy of Concordia University |
A newly identified Arctic Ocean bacterium may have an unusual way of making the building blocks it needs to grow. Using acetone, a common chemical in seawater, the bacterium incorporates carbon dioxide (\(\text{CO}_2\)) into its metabolism, allowing it to survive in waters where nutrients and usable organic matter are scarce.
In a study published in Nature Communications, Concordia researchers describe how Porticoccus arcticus survives in the frigid waters of the Beaufort Sea, just north of the Yukon in the Arctic Ocean's Canada Basin. The team found genomic evidence that the bacterial population uses acetone carboxylation, a process that converts acetone and carbon dioxide into compounds that can enter the cell's central metabolic pathways.
“This study introduces two new discoveries,” says David Walsh, a professor in the Department of Biology and the paper's corresponding author. “The first is a group of organisms, P. arcticus, that has a unique metabolism that uses organic carbon while at the same time has the capacity to use light as an energy source. We call this process photoheterotrophy.
“The second discovery is the way the organism consumes acetone to also consume carbon dioxide out of the atmosphere. This acetone-mediated inorganic carbon assimilation combines what animals do—eating food, in this case, acetone—with what plants do: fixing \(\text{CO}_2\).”
Metabolic reconstruction from the genome
Acetone is produced by marine organisms, including microscopic algae, and through chemical reactions involving sunlight and dissolved organic matter. Although scientists have identified other ways marine bacteria consume acetone, this study provides evidence of a different pathway in Arctic waters.
Genetic analyses suggest that P. arcticus has adapted to life near the ocean surface. At some locations, it accounted for up to 9 percent of detected bacteria, making it an important member of the Arctic microbial community.
The researchers note that the bacterium's relatively small genome contains the complete set of genes needed for acetone carboxylation, as well as multiple genes for light-sensitive proteins called proteorhodopsins that help cells capture energy from sunlight.
Analyses showed that genes involved in both acetone processing and light capture were among the organism's most active. The researchers say these traits may allow the bacterium to use sunlight for energy while supplementing its carbon supply through acetone metabolism and carbon dioxide assimilation.
“The genomic composition of these organisms led us to reconstruct the different types of energy and carbon metabolisms that exist,” Walsh says. “That is how we found this very specific set of genes associated with the use of acetone, which was unexpected. We discovered that the organism's genes were telling us about something we did not suspect was happening in an ecosystem. This was a surprise, as we were not actively looking for acetone-degrading bacteria that can use light.”
Localized or widespread?
Walsh does not know what the implications of a warming Arctic Ocean mean for P. arcticus, though changing sea-ice conditions could affect the bacterium's future distribution by influencing sunlight and acetone availability.
The research team will also be looking for evidence of this kind of behavior in other oceans, as well as in freshwater bacterial populations.
Susan McLatchie, MSc 2023, was the lead author of this study. PhD student Sara Palestini and research assistant Asher Woodhead, both of Concordia, along with Tony Gutierrez of Heriot-Watt University in Edinburgh, Scotland, contributed research.
Funding: The Natural Sciences and Engineering Research Council of Canada helped fund this study.
Published in journal: Nature Communications
Title: Evidence of an acetone carboxylation pathway in photoheterotrophic bacteria from the Arctic Ocean
Authors: Susan McLatchie, Sara Palestini, Asher Woodhead, Tony Gutierrez, and David A. Walsh
Source/Credit: Concordia University | Patrick Lejtenyi
Edited by: Scientific Frontline
Reference Number: mcb110326_01
