Bacteria Build with Nanomaterial Potential

Civil engineering is not a uniquely human pursuit. Throughout the ocean, from slime growing in the sunny shallows to colonies of life surrounding seafloor hydrothermal vents, microbes produce their own construction materials and build their own environments. Some of the most productive tiny architects are iron-oxidizing bacteria—microorganisms that process iron for energy, and in doing so, create complex structures made of rust.

“They make their own little cities and towns and villages,” said Dave Emerson, a senior research scientist at Bigelow Laboratory for Ocean Sciences. “We refer to them as ecological engineers.”

Iron-oxidizing bacteria that live in ocean environments with low oxygen and iron gain energy by transferring electrons between these two elements, and capturing the tiny spark of energy that results. This process produces rust minerals as byproducts, which help form twisted stalks, ribbon-like structures that grow out of the microbes.

Producing twisted stalks is essential to their survival. It stops the microbes from becoming trapped in a rust shell, anchors them in place against ocean currents, and keeps them close to their iron food source. The habitat created by the stalks is also important for other microorganisms long after the original iron-oxidizing bacteria are gone.

“When you go to New York City and see skyscrapers, you rarely see the people who built them,” Emerson said. “The people living in those skyscrapers are secondary colonizers in a sense, and iron-oxidizing bacteria are the city’s builders.”

In the case of this microbial city, it would take about a thousand stalk “skyscrapers” stacked on top of each other to be as thick as a human hair. Though the structures built by these microbes are tiny, their potential impact is huge. The stalks can both help explain Earth’s history and inspire new materials that could be important to its future.

Emerson and Elif Koeksoy, a postdoctoral scientist at Bigelow Laboratory, are excited about useful nanomaterials that could be developed from iron-oxidizing bacteria. The researchers are currently working to determine what controls the growth of twisted stalks—genetics, environmental triggers, or a combination of the two. Identifying and manipulating these controls will allow researchers to grow large batches of iron-oxidizing bacteria in the laboratory and produce nanomaterials efficiently.

“There are still big knowledge gaps about the formation of these structures,” Koeksoy said. “If we can understand and control that formation process, we can potentially make a wide range of materials with unique properties.”

The resulting nanomaterials could have broad applications. They could make synthesizing compounds and chemicals safer and more efficient. They could be installed in water filtration devices to attract heavy metals and other pollutants. The rewards of developing high-strength, lightweight nanomaterials could even extend to electronics and wearable materials.

“By using biology to accomplish tasks like making chemicals, we can avoid nasty processes that create toxic wastes,” Emerson said. “This could potentially change the way we do things like filter water and make batteries.”

Understanding the conditions that control how twisted stalks grow could also illuminate the earliest days of the planet. Many of Earth’s oldest rocks are part of the banded iron formations, layers of iron-rich sedimentary rock found around the globe. They are a significant iron ore source and mark one of the most important events in Earth history: the oxygenation of the atmosphere by photosynthetic bacteria.

Fossils that look like twisted stalks structures are layered throughout these formations. These indicate that iron-oxidizing bacteria have existed for billions of years, and may have thrived under ocean conditions created by the oxygenation of the Earth’s atmosphere.

Understanding what role iron-oxidizing bacteria played in these major events will clarify the earliest roots of life and shed light on the composition of today’s atmosphere and oceans.

“This is a critical part of ancient Earth research,” Koeksoy said. “It’s incredible that studying these microbes allows us to look at everything from single cells to global implications.”

The middle and bottom images show stalks produced by different species of iron-oxidizing bacteria. They were photographed by Dr. Clara Chan, and appear in the paper "The Architecture of Iron Microbial Mats Reflects the Adaptation of Chemolithotrophic Iron Oxidation in Freshwater and Marine Environments."