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One strain of P. aeruginosa makes green-pigmented phenazines. The bottles on the left contain bacteria engineered to lack the molecules.
That summer at Cold Spring Harbor changed the direction of Newman's research.
“I realized this huge power in genetics that could solve all these problems I was considering,” she recalls. Once at Princeton, she started characterizing the arsenic-metabolizing bacterium, which she named Desulfotomaculum auripigmentum for its gold-colored pigments. At that point, she couldn't genetically modify the microorganism, but she held on to that goal for later.
Though she worked in a geosciences lab, Newman frequented molecular biology labs to absorb techniques and advice, says Princeton's Silhavy, who had Newman as a student in his graduate genetics course. “When there were things to learn, she took it upon herself to learn them,” he says.
Newman thought that together microbiology and genetics could tackle questions that geologists had been grappling with. “A lot of geology-related microbiology until then had been very descriptive, and here was finally a way to get at underlying mechanisms.”
In 1998, Newman landed a postdoc position in the microbiology lab of Roberto Kolter at Harvard Medical School. “Her background really caught my eye,” says Kolter, who prides himself in having a diverse team. “I'd never had anyone with a degree in German studies apply to my lab.” She proposed to study bacteria that metabolize not arsenic, as she'd studied with Morel, but iron.
“I must say that I had never thought of studying this,” says Kolter. “When she first brought it up I thought ‘What's the big deal? Why is this important?' but after a few minutes with her I was convinced this was the project she should do.”
Iron is noteworthy because it was much more biologically available in the ancient, oxygen-depleted earth than it is today. Most bacteria need oxygen to survive because chemical reactions that give bacteria energy produce excess electrons. Oxygen, an electron acceptor, can collect these spare electrons. Other compounds—like iron—can accept electrons too but the mechanism was unknown before Newman started studying iron-metabolizing bacteria.
Newman had an inkling that the bacteria produced molecules that acted outside the cell as electron shuttles—carrying electrons from the cell and dumping them on iron. Her suspicions were right—she discovered evidence for such an electron shuttle by screening mutants that couldn't metabolize iron. With that finding, Newman suddenly had a plethora of options for her future.
“She arrived in my lab in January, and after she had been there less than a month, she came into my office and told me that she had three job interviews,” says Kolter. “This is how impressive she was. Nobody else at the time was thinking of combining environmental microbiology and genetics. She paved the way for a new field.”
Photo: Leah Fasten