Dianne Newman is exploring the deep connection between bacteria and rocks -- specifically, the possibility that some varieties of ancient microorganisms gave rise over millennia to vast mineral deposits. She’s intrigued in particular by enormous banded iron formations found on every continent that contain rich evidence of the important role of bacteria.

Newman and her colleagues examine this ore in big and small chunks, and from a biochemical perspective. Buried inside lie fossils of microorganisms and their processes, and it’s by the “careful interpretation of the rock record that we make progress,” says Newman. 3.4 billion-year-old rock chunks called stromatolites contain fossil shapes that look like “microbial mats rolled up,” and filaments resembling the structures some bacteria use for photosynthesis, the process by which modern-day plants split water using sunlight to produce their food. There are also molecule-scale fossils of cyanobacteria (blue green algae), a photosynthetic microorganism, preserved in 2.5 billion year old rock. In the days before atmospheric oxygen became abundant on Earth, could primitive bacteria have used a photosynthetic process based on other elements, like iron, and yielded enormous mineral deposits over time?

To learn what microbial community might have produced stromatolites and other such rocks, Newman headed down to a salt marsh in Woods Hole, to “dig in the sand and see microbial mats with various layers of bacteria” -- cyanobacteria on the top, green and purple beneath and on the bottom, sulfate-reducing bacteria. While scientists have demonstrated that the metabolism of oxygen-producing cyanobacteria stimulates the formation of calcium carbonate minerals, it has been uncertain whether the other bacteria, which don’t produce oxygen, can do the trick of creating such minerals.

Newman’s students found samples of such bacteria near a rusty staircase in Woods Hole and isolated from them a gene required for iron oxidation, part of the process of turning the element of iron into the kind of minerals found in banded iron deposits. Students cultured these bacteria, and watched mineral formations emerge in response to light. Newman ran the numbers to figure out if ancient earth oceans containing such bacteria might have produced the kind of minerals seen in banded iron formations.

The result, she reports, is “encouraging” but not yet conclusive. Ambiguity remains, because non-biological processes might also have produced these formations. For her though, “this question is profound, fascinating and hard to answer. The evolution, when, and how, of different types of photosynthesis remains a mystery, awaiting the next generation of Earth scientists and molecular biologists.”

ABOUT THE SPEAKER:
Dianne Newman explores how microbes affect the structure of the rocks in which they grow, specifically how they use minerals like arsenic and iron in their metabolism. It's an area of research that is yielding new insight into the earliest forms of life while offering a framework for studying the phenomenon of bacterial biofilms.

She studies how anaerobic bacteria survived millions of years ago, before the atmosphere contained oxygen. These bacteria, in essence, "breathed" iron, and Newman focuses on how they used it in the electron transfer process that was fundamental for their metabolism.

Newman received a B.A in German studies from Stanford University, and a Ph.D., in Civil and Environmental Engineering, from MIT. She has been a David and Lucile Packard Fellow in Science and Engineering, and won the Young Investigator Award from the Office of Naval Research.