NATURE|Vol 451|10 January 2008
BACTERIA’S NEW BONES
Long dismissed as featureless, disorganized sacks, bacteria are now revealing a multitude of elegant internal structures. Ewen Callaway investigates a new field in cell biology.
early a decade ago Jeff Errington, a microbiologist at Newcastle University in England, was toying with a strange bacterial protein known asMreB. Take it away from microbes, and they lose their characteristic cylindrical shape. The protein’s obvious role in structure and even its sequence suggested a shared ancestry with actin, a protein that produces vast, fibrous networks in complex cells, forming the framework of their internal structure, or cytoskeleton. But no one had ever seen MreB in action under the microscope until Erringtonfound just the right combination
of fluorescent labels and fixatives. In a 2001 paper, he presented MreB (orange in the illustration below) fluorescing brilliantly and painting barbershop-pole stripes around the rod-shaped bacterium Bacillus subtilis1. “We got these amazing pictures. It was one of those few times in a scientific career when you do an experiment that completely changes your wayof thinking,” says Errington. For more than a century, cell biology had been practised on ‘proper’ cells — those of the eukaryotes (a category that includes animals, plants, protists and fungi). The defining characteristic of eukaryotic cells is their galaxy of
internal structures: from the pore-studded nucleus that contains the genome, to the fatty sacs of the Golgi, to the myriadmitochondria, and of course the networks of protein highways that ferry things around the cell and give it shape and the capacity for movement. These elements form a catalogue of cell biology’s greatest discoveries, and all of them are absent in bacteria. Hundreds to thousands of times smaller than their eukaryotic cousins, and seemingly featureless, bacteria were rarely invited to the cell biology party. ButErrington’s discovery has been part of a movement that is changing that.
Bacteria appear to have sophisticated internal structures that give them shape, and help them grow and divide.
NATURE|Vol 451|10 January 2008
Dyche Mullins, a cell biologist at the University of California, San Francisco had spent most of his career untangling the network ofmolecular cables and scaffolding that enforces order in the eukaryotic cell. With Errington’s paper, Mullins saw the lowly bacterium anew. “There was a lot of organization in bacterial cells we were just missing,” he says. He has since devoted much of his time to studying them. Last month, Mullins chaired the annual meeting of the American Society for Cell Biology in Washington DC. That he was chosen forthe job is a clear indication that bacteria have made it on to the guest list. Lucy Shapiro, a microbiologist at Stanford University in California gave bacteria an hour-long tribute at the meeting. “People more or less thought the bacterial cell was a swimming pool and the chromosome was this ball of spaghetti,” says Shapiro, whom many credit for launching the field of bacterial cell biology.SPHERICAL/COCCOID
HOW BACTERIA GET IN SHAPE
Scientists learn the most about cell shape when things go wrong. Take the spherical Staphylococcus aureus. The bacterial tubulin protein FtsZ makes a ring around the bacterium’s equator that helps the cell to split. If the gene for FtsZ is removed, cells begin laying new cell-wall bricks everywhere. Eventually, the bacteria swell to eighttimes their volume before bursting. FtsZ may keep the cell wall’s builders focused on moulding new hemispheres.
Complicated morphs are likely to involve the cytoskeleton, but scientists have so far found only one example, the curve of a Caulobacter bacterium, made with an ancestor of a eukaryotic intermediate filament protein called crescentin. Remove the protein, and crescent turns to...