University of California San Diego biologists imaged the oscillations of cell growth (displayed as different colored lines) from a biofilm growing outward from the center. (Courtesy of Suel Lab/UC San Diego)

Bacteria may make you sick, create plaque on your teeth and turn your breath rancid — but nobody can call them selfish. At least, that's what some scientists are saying.

A new study, published this week in Nature, says bacteria living in colonies are actually pretty good at caring for their fellow microbes. Its authors say the life forms balance the opposing needs of individuals against the survival of the entire community by managing resources like space and food.

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The scientists focused on a phenomenon that occurs as growing bacterial populations expand outward. If growth goes unchecked, bacteria on the outer edge of the colony eat up all of the food, starving the interior cells.

But they've come up with a way to counter that. Interior cells produce ammonia — a metabolic signal — that periodically puts the brake on outer cell growth, giving everyone access to nutrients and creating an oscillation in growth rates.


A bacteria community shows its oscillating growth pattern. (Courtesy of UC San Diego)

The strategy is similar to how people manage traffic at intersections by taking turns. Scientists call this behavior an "emergent phenomenon," meaning you can't observe it if you were only looking at individuals.

[Life would go on if all bacteria disappeared (but it would totally suck)]

Scientists were previously puzzled as to why bacteria produced massive amounts of ammonia when under stress or starving. Put into the context of the whole community, though, and the chemical becomes an essential device for communication between the thousands of cells.

"It's something that emerges just out of the complexity of the system," said Gurol Suel, an author of the study and a professor at the University of California San Diego.


Suel compares the discovery to a medieval castle. The bacteria — although genetically identical to one another —take up different roles. Some act like soldiers on protective walls and others acting like peasants inside. They all have their own division of labor — even if they're not aware of it — and it's all for the survival of the whole.

"For millions of years [the microbes] have been expecting an attack," Suel said. "It's like building a bomb shelter so tight that there would be no air in it. Periodically they open the door."

He suggests we humans take a moment to reflect on what this discovery can mean to our society about managing conflict.

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*Pause here to reflect. Beautiful, isn't it?*

But this beautiful cooperation also makes bacterial colonies hard to kill: They're just so darn altruistic! Now that scientists have figured out the bacteria's master strategy, they hope to develop a new method of attack, especially against antibiotic resistant species.

"These bacteria are clever," Suel said. "They've survived millions of catastrophes. We're running out of drugs that can kill bacteria, and people are looking for new ideas."

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UC San Diego has submitted a patent application to license the discovery, with the hope that it could lead to new methods of making outside cells more selfish and willing to grow without hesitation. At the same time, their friends in the core of the population will wither away and die.

"Then we just chip away at the wall, and that's easy," Suel said.

It's possible, he says, that similar strategies could be used to fight cancerous tumors.

More research on this discovery is to come, and the expectation is that this concept applies not only to all other bacteria species living in communities, but to all of life. Similar to other metabolic processes discovered in bacteria, this could lay the groundwork for a theory on how single-celled organisms built the tools to become multicellular organisms, like us.

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