THE secret of how some bacteria move around without the equivalent of arms and legs has finally been solved. A researcher in California has shown that they are rocket propelled鈥攂y slime.
For years researchers thought that the soil-dwelling myxobacteria and cyanobacteria use slime as a lubricant, just as slugs do. The real power, they thought, came from little sticky hairs called pili that pull the bacteria forward as they contract.
But in 1979, researchers at Stanford University created mutant forms of the soil myxobacteria that didn鈥檛 have any pili. To their surprise, the bacteria were still mobile. The puzzled researchers couldn鈥檛 understand how slime alone could push a cell through soil. 鈥淚t鈥檚 hard to see how a cell could push itself along with a wet noodle,鈥� says Stanford biologist Dale Kaiser.
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But Charles Wolgemuth, a biophysicist at the University of California, Berkeley, says he鈥檚 worked out what鈥檚 happening. Together with colleagues George Oster and Egbert Hoiczyk at Rockefeller University in New York, he looked at the nanometre-sized nozzle-shaped orifices that exude slime in both myxobacteria and cyanobacteria.
Oster realised that the slime鈥攁 polysaccharide gel鈥攅xuded by the bacteria contains a lot of water. The bacteria probably create the gel from dehydrated sugar molecules stored in a cavity next to the orifices. When water enters the cavity, the gel swells up and pushes against the internal side of the cavity. 鈥淚t鈥檚 exactly like making jello in a mould,鈥� says Kaiser.
When the slime emerges from the orifice it pushes the bacterium in the opposite direction. Wolgemuth calculates that because the gel more than doubles in size as it gets hydrated, each orifice fires with a force of around 1 piconewton, more than a hundred times the weight of the cell it propels. He told the meeting that each bacterium has about 100 orifices, and the force of them all firing together propels the cell along at several micrometres per second.
Kaiser says the ability of myxobacteria to get around is crucial to their propagation. The bacteria swarm together to produce tree-shaped structures that deposit packages of spores onto passing worms or insects. He鈥檚 now hoping to build on Wolgemuth鈥檚 idea by studying the genes involved in making the slime.