Natural Sorting Mechanism Allows Bacteria to Preserve Diversity

Diversity in bacteria — and in all forms of life — ensures the ability to survive random changes in the environment. But when a bacterial band begins to migrate, individual cellular differences present a problem: What happens to the slowpokes?

Yale University researchers have discovered a natural sorting mechanism that allows colonies of E. coli to preserve individual differences, yet move in concert while migrating over long distances. They report their findings on June 5 in the journal Nature Communications.

“Cancer cells are all diverse, which helps them survive efforts to eradicate them, but they also move in concert in the body,” said senior author Thierry Emonet, associate professor of molecular, cellular & developmental biology and physics. “Birds are individuals, but when they flock they move together in unison. We found how bacteria can act in the same way.”

The Yale team tracked groups of E. coli cells as they chase food that recedes as they consume it. At the head of the group, food is plentiful. Behind it, nothing is left. In a process called chemotaxis, cells detect this difference and move accordingly, which results in collective migration.

When researchers reduced the available food, fewer slow-moving cells could keep up with the group. “The minimum speed required to stay with the group increases,” Emonet said. “This is exactly what we see in human society during times of want — the weakest have a hard time keeping up with a migrating group.”

However, the study showed that not all of the slow-moving cells were left behind. The fastest cells swam to the front of the group, where only weak cues guided which direction to go. The slowpokes swam behind them, where differences in food abundance were clearer. Matching of swimming ability to the strength of the cues allowed the diverse cells to migrate together at the same speed.

The observation not only has applications for the study of pathologies like cancer or infections, said the researchers, but is a reminder about the delicate balance in all forms of life between preserving diversity and the need for concerted action.

“If individual differences are sacrificed, then the colony might not survive in new circumstances,” Emonet said. “But if unchecked individualism dominates, critical collective behavior necessary for survival breaks down.”

Lead authors of the paper are: Xiongfei Fu and Setsu Kato, formerly of the Emonet lab and now at the Shenzhen Institutes of Advanced Technology (China) and Hiroshima University (Japan), respectively.

The research was primarily funded by The National Institute of General Medical Sciences and by the Allen Distinguished Investigator Program through The Paul G. Allen Frontiers Group.

Reference: “Spatial self-organization resolves conflicts between individuality and collective migration” by X. Fu, S. Kato, J. Long, H. H. Mattingly, C. He, D. C. Vural, S. W. Zucker and T. Emonet, 5 June 2018, Nature Communications.
DOI: 10.1038/s41467-018-04539-4

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