When times get hard, bacterial communities don't go to war. Instead, in the right circumstances, they engage in a time-sharing arrangement, feeding in a way that maximizes the chance of all surviving.
Last year, Professor Gürol Süel of the University of California, San Diego, announced that bacteria can communicate with each other using electrochemical signals similar to those seen in animal nerve cells. Bacteria at the center of a colony, with little access to food, use potassium ions to send messages to tell those expanding into territory rich in the nutrient glutamate to wait up and share some of the bounty with their starving fellow colony members.
That discovery was surprising enough, but Süel's latest work is stranger still. Two physically separated bacterial colonies communicate through pulses traversing the intervening material to coordinate their growth.
In Science, Süel reports that when two biofilm communities of Bacillus subtilis are placed 2 millimeters apart on a slide stocked with glycerol and glutamate, their patterns of growth and consolidation came to have the same period. Eventually, these oscillations became out of phase, so that as one community grew the other distributed food and vice versa. This allowed the communities to consume food in the most efficient manner and maximize the growth of each.
"What's interesting here is that you have these simple, single-celled bacteria that are tiny and seem to be lonely creatures, but in a community, they start to exhibit very dynamic and complex behaviors you would attribute to more sophisticated organisms or a social network," Süel said in a statement. "It's the same time-sharing concept used in computer science, vacation homes and a lot of social applications."
"It's interesting to think that these simple organisms 2 billion years ago developed the same time-sharing strategy that we humans are now using for all kinds of purposes," he added.
The authors explain that even when the two colonies appear to end their growth phases simultaneously, one will be slightly earlier. “This will allow the second biofilm to postpone halting its own growth, thus increasing the phase difference between the biofilms,” the paper notes. Gradually, the time gap expands until the two are perfectly out of phase.
However, this process only occurred when glutamate concentrations were low. The benefits of out-of-phase oscillations were so great that colonies exposed to glutamate shortages actually grew faster than those growing in glutamate-rich conditions. Learning to cooperate outweighed the drawbacks of food shortages.
Süel intends to study whether colonies from different species can coordinate in the same way. However, he will probably never answer why if mindless single-celled creatures can put aside their differences to collaborate, humans are so bad at doing likewise?