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. 鈥淭heir gliding
motion was a complete puzzle and has been very neglected,鈥� 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.
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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. 鈥淭he cells leave behind a rigid strand that you can eventually detach
from the surface,鈥� says Baumeister.
The cells of both species of cyanobacteria that the researchers studied form
filaments鈥攍ong 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鈥攐ne 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).
鈥淲e now know the engine they use for locomotion,鈥� Baumeister concludes. 鈥淏ut
we don鈥檛 know how the bacteria decide which direction to take.鈥� Bacteria are
known to be able to 鈥渟niff out鈥� sources of food
(see 鈥淕et the message鈥�, New 杏吧原创, 15 August, p 40),
and Baumeister鈥檚 hunch is that this helps the bacteria to choose where to go.
