Crescent-shaped bacteria reveal their secrets

Caulobacter cells

Inside the Caulobacter cell (green), CTP Synthase (red) forms filaments that curve the normally straight cells. (Image courtesy of Michael Ingerson-Mahar)

Nature is nothing if not green. It reduces, reuses and recycles whenever possible. Now Princeton researchers have discovered that bacteria can repurpose proteins used for cell growth into structural supports that maintain cell shape.

“We’ve identified a bacterial species that appears to have stolen something that evolved for a regulatory purpose and started using it for a structural purpose,” said Zemer Gitai, an associate professor of molecular biology. “This discovery hints at a paradigm for how structures such as the cytoskeleton have evolved.”

Gitai and his team found that a protein called CTP synthase — known to be crucial for producing the nucleic acid RNA that is essential for cell growth and energy — also keeps the cells of the bacteria Caulobacter crescentus in their distinctive crescent-roll shape. The researchers were among the first to discover that many of the cells’ proteins are fixed in place rather than free-floating inside the cell. CTP synthase was one of the proteins they had expected to see located throughout the cell.

The researchers observed that CTP synthase instead links up to form wispy, spider silk-like strings that are stocks of premade enzymes. Gitai theorized that they are a cell’s way of storing the enzymes for times when the cell needs to make new RNA quickly. The researchers found that C. crescentus’ shape is due to shortened CTP synthase strings on one side of the cell, which force the normally straight bacterium to curl into a crescent. The research was published in the journal Nature Cell Biology in August 2010, and supported by the U.S. Department of Energy Office of Science, the Human Frontiers Science Program and the Arnold and Mabel Beckman Foundation.

Eventually, Gitai said, studies of how cells create their own shapes and structures could aid our understanding of self-assembly, a feat common in nature but very unlike how humans build things. “We humans can learn a lot from studying how the cell accomplishes this feat,” he said.