In nature, the bacterium Geobacter sulfurreducens uses these nanowires, called pili, to transport electrons to remote iron particles or other microbes, but the benefits of these wires can also be harnessed by humans for use in fuel cells or bioelectronics.
The study in mBio® reveals that a core of aromatic amino acids are required to turn these hair-like appendages into functioning electron-carrying biological wires.
"It's the aromatic amino acids that make it a wire," says lead author Derek Lovley of the University of Massachusetts, Amherst. Lovley and his colleagues removed the pivotal amino acids from the pili and replaced them with smaller, non-aromatic amino acids. Without these key components, Lovley says, the pili are nothing more than protein strings. "We showed it's not good enough to just make the string - you've got to make a wire," says Lovley.
G. sulfurreducens "breathes" by removing electrons from organic materials and funneling them to iron oxides or to other microorganisms, much the way humans pull electrons out of organic molecules in food and dump them on oxygen. The bacteria use their pili to reach out to iron oxides or other microbes, transferring the "waste" electrons along the structure to the destination. Geobacter's pili are only 3-5 nanometers wide, but they can be 20 micrometers long, many times longer than the cell itself.
Trafficking in electrons is how all living things breathe, but it is normally carried out by discrete proteins or other molecules that act like containers for shuttling electrons from one place to another. Lovley says earlier results showed the pili in G. sulfurreducens possess metallic-like conductivity, the ability to carry electrons along a continuous structure, a controversial finding in biology.
To investigate how pili accomplish this singular feat, Lovley says they looked to non-biological organic materials that can conduct electricity. "In those synthetic materials, it's aromatic compounds that are responsible for the conductivity. We hypothesized that maybe it's similar in the Geobacter pili. In this case, it would be aromatic amino acids." Aromatic compounds have a highly stable ring-shaped structure made of carbon atoms.
Turning to the pili, Lovley says his group looked for aromatic amino acids in the parts of the pili proteins that would most likely contribute to the conductivity. Using genetic techniques, they developed a strain of Geobacter that makes pili that lack aromatic amino acids in these key regions, then they tested whether these pili could still conduct electricity. They could not. Removing the aromatic amino acids was a bit like taking the copper out of a plastic-covered electrical wire: no copper means no current, and all you're left with is a string.
Removing aromatic amino acids from the pili prevents the bacteria from reducing iron, too, says Lovley, an important point because it adds further proof that Geobacter uses its pili as nanowires for carrying electrons to support respiration.
Metal reducers like Geobacter show a lot of promise for use in fuel cells, says Lovley, and by feeding electrons to the microbes that produce the methane, they're an important component of anaerobic digesters that produce methane gas from waste products. Understanding how they shuttle their electrons around and how to optimize the way the pili function could lead to better technologies.
Moving forward, Lovley says his own lab plans to explore the possibilities of biological nanowires, exploring how to make them more or less conductive.
mBio® is an open access online journal published by the American Society for Microbiology to make microbiology research broadly accessible. The focus of the journal is on rapid publication of cutting-edge research spanning the entire spectrum of microbiology and related fields. It can be found online at http://mBio.asm.org.
The American Society for Microbiology is the largest single life science society, composed of over 39,000 scientists and health professionals. ASM's mission is to advance the microbiological sciences as a vehicle for understanding life processes and to apply and communicate this knowledge for the improvement of health and environmental and economic well-being worldwide.
Jim Sliwa | EurekAlert!
Newly designed molecule binds nitrogen
23.02.2018 | Julius-Maximilians-Universität Würzburg
Atomic Design by Water
23.02.2018 | Max-Planck-Institut für Eisenforschung GmbH
A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.
In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...
A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.
By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...
Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
23.02.2018 | Physics and Astronomy
23.02.2018 | Health and Medicine
23.02.2018 | Physics and Astronomy