Groups of highly social bacteria found to maintain order by periodically reversing direction, says a collabrative study.
Microbiologist Dale Kaiser of Stanford University in California and Mark Alber at the University of Notre Dame in Indiana say that groups of myxobacteria change direction at regular intervals in search of food, heading back in the direction of the bacterial colony from which they came before returning to their original course.
They highlighted the fact that scientists had for long been puzzled by the very movement, and wondered why the bacteria would waste energy retracing their steps.
They claimed that their team had developed a model showing that without such periodic reversals, swarms of Myxococcus xanthus would become disordered and move at a slower rate, eventually coming to a standstill.
The researchers said that their findings might be helpful in studying traffic flow, in teaching robots to move in groups, or inventing new biological engines.
"Reversing seems like a silly thing to do. It seems like it would get them nowhere. But, in fact, it gets them everywhere," Nature magazine quoted Kaiser as saying.
The computational model made by the researchers takes into account the behaviour and cell biology of M. xanthus, and it shows that swarms expand at the greatest rate when cells reverse direction roughly every eight minutes, matching the timing observed in the organism.
The researchers said that, over time, the reversals generate a more orderly swarm, with more cells in parallel, making them less likely to bump into one another.
When the researchers allowed the cells in the model to move, but not to reverse direction, they jammed together and became unable to swarm.
Published in the Proceedings of the National Academy of Sciences, the findings suggest that reversing direction gives the bacteria information about their neighbours' locations, and allows the group to maintain formation, even in the absence of information about the swarm as a whole.
Meanwhile, although the group loses some distance each time it turns back, its movement in that direction is impeded as more cells are shed from the colony, and ultimately there is still a net movement outwards.
"Individual cells use a lot of energy for reversals, but still it's beneficial for the whole population," says Alber.