If they're right, their insight could have broader implications, because it addresses what Newman calls "a generic problem bacteria face growing on any surface." Few bacteria dwell on their own. No matter where and how they get their energy--whether they savor the sugars in the crevices of your teeth or slurp sulfur from undersea vents--most bacteria live in thick, clingy communities called biofilms. Inside a biofilm, some of them will be closer than others to the chemicals they need to conduct their energy-producing reactions. As Newman thought about the way iron-breathing bacteria use electron shuttles to transport their electrons from deep within a biofilm to a rock surface, she realized that bacteria growing in biofilms in our bodies might do something similar.

Newman decided to test the importance of phenazines produced by the human pathogen Pseudomonas aeruginosa, which causes serious chronic infections in people who have cystic fibrosis or whose immune systems have been compromised. Living in the lungs, these bacteria would run into the same problem as the rock breathers worlds away: those in the middle of the biofilm would be isolated from an important energy substrate, in this case oxygen.

To test whether these bacteria could use phenazines to overcome the challenges of communal living, researchers in Newman's lab engineered two mutant strains of them. One strain couldn't make phenazines, while the other made them in great quantities. When ­Newman and her collaborators grew the bacteria in petri dishes, they saw differences in the architecture of their communities. The overproducing strain grew in a tight, smooth layer, spread out like Los Angeles. The phenazine-free strain also spread out over a large area but grew in high towers, built up like New York City--presumably to maximize each cell's exposure to the oxygen in the air.

These results are promising; now Newman must perform tests to see how the two mutant strains grow in the lung. If Pseudomonas needs phenazines to survive, researchers could, in theory, develop therapies that prevent the bacteria from synthesizing or making use of them; that could help eradicate chronic infections.

"Accessing oxygen today is just as much a problem as accessing a mineral was in the past," Newman says. It's just such connections that make geobiology a rich and surprising vein of knowledge, not just about the planet's history but about our present.