Bacteria do the twist.

Most bacteria are shaped like rods or spheres, but some assume curved or helical forms. A newly identified bacterial protein dubbed crescentin generates the sinuous shapes, a new study indicates.

Until about 4 years ago, microbiologists hadn't realized that the shape of bacterial cells is determined by an internal skeleton of protein filaments similar to those that give form to animal cells. That's when researchers discovered that bacteria have their own versions of actin and tubulin, proteins that make up two different filament types in animal cells (SN: 6/08/02, p.366). Now, Christine Jacobs-Wagner of Yale University and her colleagues report that crescentin forms strands resembling intermediate filaments, which are yet another component of the skeleton in animal cells.

The researchers identified crescentin while studying Caulobacter crescentus, which comes in curved or helical forms, depending on its length. Mutant forms of the bacterium that lack the protein assume a rodlike shape, the biologists discovered. Adding the gene for crescentin to these mutant microbes returned them to their curvaceous form, the team reports in the Dec. 12, 2003 Cell.

It's not yet clear whether crescentin strands gave rise to the intermediate filaments in animal cells or whether those filaments evolved independently, says Jacobs-Wagner. The researchers are now investigating what survival advantage the curved shape might bestow upon C. crescentus.--J.T.