Microbial Carboxysomes: Key to Understanding Ocean Carbon Cycle

Members of these tiny phytoplankton species are able to utilize a broad range of light intensities.

The Science

Bacteria play a key role in sequestering carbon dioxide (CO2) in the oceans. In particular, Prochlorococcus cyanobacteria are considered the world’s most abundant photosynthetic organisms, able to convert sunlight to energy at ocean depths of up to 200 meters. Despite their small size, they are estimated to contribute up to half of all marine biological carbon sequestration. This microbe’s ability to use carbon is attributed in part to the RuBisCO enzymes that fix CO2 and are stored in microcompartments known as carboxysomes. Learning about these tiny cellular structures can help researchers understand how their composition and design support their function, contributing to a better understanding of the ocean carbon cycle. Scientists at the University of Mississippi, the DOE Joint Genome Institute (JGI), and University of California–Berkeley report the first successful purification and characterization of these carboxysomes from a strain of P. marinus. Comparisons against 29 cyanobacterial genomes in a phylogenetic assay suggested, based on the numbers and types of genes that the team identified, that the carboxysome’s structure is more complex than had been previously assumed. “Our findings have important implications for the structure, function, and regulation of α-carboxysomes and suggest that the protein composition of these important bacterial organelles warrants a closer look beyond what was assumed to be a solved problem,” the team concluded.

Principal Investigator

Sabine Heinhorst
University of Southern Mississippi

BER Program Manager

Ramana Madupu

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Roberts, E. J., F. Cai, C. A. Kerfield, G. C. Cannon, and S. Heinhorst. 2012. “Isolation and Characterization of the Prochlorococcus Carboxysome Reveal the Presence of the Novel Shell Protein CsoS1D,” Journal of Bacteriology 194(4), 787-95. DOI: 10.1128/JB.06444-11.