Because they are so abundant, cyanobacteria play a major role in the earth's carbon cycle, the movement of carbon between the air, sea and land. "A significant fraction of global carbon fixation takes place in carboxysomes," said Kerfeld. Cyanobacteria, along with plants, impact climate change by lowering the amount of carbon from the atmosphere and depositing it in organic matter in the ocean and on land.
In order to track carboxysome assembly, the first author, Jeffrey Cameron, developed what Kerfeld called "an inducible system to turn on carboxysome biogenesis." He first developed mutant strains of a Synechococcus cyanobacterium that had its genes for building carboxysomes intentionally broken and then introduced the products of each of the knocked-out genes, which had been tagged with a fluorescent marker. He captured time-lapse digital images of the bacteria a technique called time-lapse microscopy -- as they used the glowing building blocks and incorporated them into their new carboxysomes. The research team also painstakingly took high resolution still photographs using a transmission electron microscope of the intermediate stages of carboxysome construction. With these detailed images, they were able to provide a specific role for each product of each knocked-out gene, along with a timeline for how the bacteria built its carboxysomes. The team also suggested that other bacteria might build different types of microcompartments the same way carboxysomes are built, from the inside out.
It's the first time scientists have been able to watch bacterial organelles as they are built by living cells. Kerfeld noted that not only is the filming technique a major advance over previous methods, but that there are far-reaching implications for this work.
|Contact: David Gilbert|
DOE/Joint Genome Institute