Microbiologists Help Advance Development of 'Green' Electronics Using Microbial Nanowires

An artist's rendition of Geobacter expressing electrically conductive nanowires. Microbiologists at UMass Amherst have discovered a new type of natural wire produced by bacteria that could greatly accelerate the development of sustainable "green" conducting materials for the electronics industry. (Credit- UMass Amherst)

A new type of natural wire formed by bacteria has been discovered by microbiologists at the University of Massachusetts Amherst. This could significantly accelerate the goal of researchers to develop sustainable “green” conducting materials for the electronics sector.

The research by Derek Lovley and colleagues has been featured in mBio, the American Society of Microbiology’s premier journal.  

The researchers examined microbial nanowires, which are actually protein filaments naturally used by bacteria to form electrical connections with other minerals or microbes.

Microbial nanowires are a revolutionary electronic material with substantial advantages over man-made materials. Chemically synthesizing nanowires in the lab requires toxic chemicals, high temperatures and/or expensive metals. The energy requirements are enormous. By contrast, natural microbial nanowires can be mass-produced at room temperature from inexpensive renewable feedstocks in bioreactors with much lower energy inputs. And the final product is free of toxic components. Microbial nanowires therefore offer an unprecedented potential for developing novel materials, electronic devices and sensors for diverse applications with a new environmentally friendly technology. This is an important advance in microbial nanowire technology. The approach we outline in this paper demonstrates a rapid method for prospecting in nature to find better electronic materials.

Derek Lovley, University of Massachusettes Amherst

So far Lovely’s lab has been studying the nanowires of only one bacterium, Geobacter sulfurreducens. “Our early studies focused on the one Geobacter because we were just trying to understand why a microbe would make tiny wires,” Lovley says. “Now we are most interested in the nanowires as an electronic material and would like to better understand the full scope of what nature may have to offer for these practical applications.”

When his lab started focusing on the protein filaments of other Geobacter species, they were amazed to discover a variety of conductivities. For instance, one species retrieved from uranium-contaminated soil formed weak conductive filaments. But, another species, Geobacter metallireducens formed nanowires that were 5,000 times more conductive than the G. sulfurreducens wires.

Geobacter metallireducens coincidentally was the first Geobacter to be isolated. Lovley recalls, “I isolated metallireducens from mud in the Potomac River 30 years ago, and every couple of years it gives us a new surprise.”

In their new study, which was supported by the U.S. Office of Naval Research, they did not analyze the G. metallireducens strain directly. Instead, they chose the gene for the protein that assembles into microbial nanowires from it and incorporated this into G. sulfurreducens.

Genetically modified G. sulfurreducens that expresses the G. metallireducens protein was the outcome, making nanowires a lot more conductive than G. sulfurreducens would naturally create.

We have found that G. sulfurreducens will express filament genes from many different types of bacteria. This makes it simple to produce a diversity of filaments in the same microorganism and to study their properties under similar conditions. With this approach, we are prospecting through the microbial world to see what is out there in terms of useful conductive materials. There is a vast reservoir of filament genes in the microbial world and now we can study the filaments produced from those genes even if the gene comes from a microbe that has never been cultured.

Derek Lovley, University of Massachusettes Amherst

The researchers explain that the G. metallireducens nanowires have extremely high conductivity due to its greater quantities of aromatic amino acids. Tightly packed aromatic rings seem to be a main component of microbial nanowire conductivity, and more aromatic rings perhaps would better connections for electron transfer along the length of the protein filaments.

The high conductivity of the G. metallireducens nanowires makes it a potential material for electronic devices, construction of conductive materials, and sensors for environmental or medical applications. The authors say discovering more about the mechanisms of nanowire conductivity “provides important insight into how we might make even better wires with genes that we design ourselves.”

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