Saying Goodbye to Planet Earth

Jeff Gore, a biophysicist at the Massachusetts Institute of Technology, and his colleagues Christoph Ratzke and Jonas Denk, report that when a sample of Paenibacillus sp., a soil bacteria, is fed a diet of glucose and nutrients in the laboratory and allowed to grow at will, the microbes end up polluting their local environment so quickly and completely that the entire population soon kills itself off.

In essence, the researchers said, the microbes commit “ecological suicide.” ...


“The effect is so dramatic,” Dr. Gore said. “You have an exponential growth of the population followed by exponential death.” Within 24 hours of the onset of the death spiral, he said, “no viable cells were left in the entire culture.”

It’s not that the microbes had exhausted their resources: Food remained to feed on. But in gorging heedlessly on the glucose bounty, each bacterium had secreted a steady flow of acidic waste into the culture medium, until the ambient pH level had plunged lethally low.

“It’s a strong pH change,” Dr. Gore said. “The cells don’t realize what they’re doing in time to stop doing it.”

Nor was Paenibacillus the only microbe found capable of committing eco-suicide. Testing a series of bacterial strains isolated from soil, the researchers found that about a quarter of them, if given the chance, would alter the acidity of their surroundings to the point of mass extinction.

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By the standard dogma, she said, inhibitory processes would intervene before an entire bacterial population is wiped out, with at least a scattering of microbes going quiescent, forming spores or otherwise waiting out the catastrophe until prevailing conditions improved.

The new research suggests that extinction is more easily set in motion than previously thought, and that once it gets started, the responsible parties may be helpless to make it stop....