On the trail

2019-03-08 10:07:21

By Andy Coghlan THE mystery of how the microorganisms called cyanobacteria get around has been solved by a pair of microbiologists in Germany. The researchers say that the bacteria squirt out small threads of slime from tiny pores, which they use to push themselves forwards through fluids. Most types of bacteria swim through fluids by rotating miniature hair-like propellers called flagella. But the movements of alga-like cyanobacteria, which have no visible means of locomotion, were much harder to crack. “Their gliding motion was a complete puzzle and has been very neglected,” says Wolfgang Baumeister of the Max Planck Institute for Biochemistry in Martinsried. According to Baumeister, microbiologists have long known that cyanobacteria can move only if attached to a solid surface. The organisms have a slimy sheath made of a sticky, sugary polymer, and the researchers suspected that this might be a key factor in how they move. To test their idea, Baumeister and his colleague Egbert Hoiczyk stained the slime threads of two species of cyanobacteria, Phormidium uncinatum and Anabaena variabilis, with black ink. They were then able to see 3 micrometres of the slime being squirted out each second. This matches the average speed of movement of the gliding cyanobacteria. The researchers say that the cyanobacteria began each journey by anchoring one end of a slime thread to a solid surface. They then shunted themselves farther and farther away from the solid surface as they squirted out their trail of slime. “The cells leave behind a rigid strand that you can eventually detach from the surface,” says Baumeister. The cells of both species of cyanobacteria that the researchers studied form filaments—long strings of cells connected together. Hoiczyk, who is now based at Rockefeller University in New York, discovered that at each junction between two bacteria, there are two sets of slime jets—one pointing obliquely backwards and one pointing obliquely forwards. Using an electron microscope, he found that the jets are tiny pores just 80 nanometres long, which extend through the multilayered cell wall into the interior of the bacterial cell. To move, the cells squirt slime either backwards or forwards in unison, propelling the filament of cells along. The scientists report their results in Current Biology (vol 8, p 1161). “We now know the engine they use for locomotion,” Baumeister concludes. “But we don’t know how the bacteria decide which direction to take.” Bacteria are known to be able to “sniff out” sources of food (see “Get the message”, New Scientist, 15 August, p 40),