Protein Nanowires Found In Diverse Microbes

Microbially produced protein nanowires are of interest because of their important role in biogeochemical processes, bioremediation, and conversion of wastes to methane or electricity. Protein nanowires harvested from microorganisms show promise as a sustainable source of electronic materials with many potential advantages over abiotic nanowire materials in sensing and other applications. Until now, Geobacter species were the only known source of protein nanowires. Geobacter nanowires are type IV pili, which are assembled from a pilin monomer that is several fold shorter than the pilin monomers found in most microorganisms. It was previously thought that the truncated pilin monomers were required to enable tight packing of the aromatic amino acids that are essential for conductivity of the Geobacter wires.  New research reveals that some larger pilin monomers can also assemble into protein nanowires that are as conductive as those that form from the Geobacter pilin monomers. Essential properties are an abundance of aromatic amino acids and no large gaps between the aromatic amino acids in the pilin monomer. These results suggest that the capacity for electrical communication with other cells or minerals has independently arisen multiple times in the evolution of diverse microbial groups and that electrical communication via protein nanowires is widespread in the microbial world. The new classes of protein nanowires being discovered offer expanded options for the fabrication of novel, nanowire-based electronic devices.


Recent Findings

Selected Press Coverage

Basic Science with an Applied Product

Geobacterspecies are of interest because of their novel electron transfer capabilities, the ability to transfer electrons outside the cell and transport these electrons over long distances via conductive filaments known as microbial nanowires.  Geobacters have a major impact on the natural environment and have practical application in the fields of bioenergy, bioremediation, and bioelectronics.

Geobacter-Fe © 2005 eye of science

The first Geobacter species (initially designated strain GS-15) was isolated from sediments in the Potomac River, just down stream from Washington D.C. in 1987. This organism, which is known as Geobacter metallireducens, was the first organism found to oxidize organic compounds to carbon dioxide with iron oxide as the electron acceptor. In other words, Geobacter metallireducens gains its energy by using iron oxide (an abundant rust-like mineral in soils and sediments) in the same way that humans use oxygen. As outlined in the publication links, Geobacter metallireducens and other Geobacter species that have subsequently been isolated from a wide diversity of environments provide a model for important iron transformations on modern earth and may explain geological phenomena, such as the massive accumulation of magnetite in ancient iron formations.

Bioremediation Geobacter species are also of interest because of their role in environmental restoration. For example, Geobacter species can destroy petroleum contaminants in polluted groundwater by oxidizing these compounds to harmless carbon dioxide and can remove radioactive metal contaminants from groundwater.  As understanding of the functioning of Geobacter species has improved it has been possible to use this information to modify environmental conditions in order to accelerate the rate of bioremediation.

Bioenergy  Geobacter species play an important role in some anaerobic wastewater digesters degrading organic contaminants with electron transfer to microorganisms that produce methane, an important biofuel.  Recent results suggest that this electron transfer proceeds through Geobacter’s conductive microbial nanowires.  The ability of Geobacter species to oxidize organic compounds with electron transfer to electrodes shows promise as a strategy for producing bioelectricity, especially in remote environments.

Microbial Electrosynthesis This is a process for converting the greenhouse gas carbon dioxide to transportation fuels and other useful organic products.  When driven with solar technology microbial electrosynthesis is an artificial form of photosynthesis that offers the possibility of converting sunlight and carbon dioxide to desirable organic compounds much more efficiently and more sustainably than biomass-based processes.

Bioelectronics Geobacter species have novel electronic properties that may have practical applications.  For example, they can form highly cohesive conductive films that have conductivities that rival those of synthetic conductive polymers. The conductivity of the Geobacter films results from a network of microbial nanowires, thin (ca. 3 nm) protein filaments that conduct electrons along their length with metallic-like conductivity.  Thus, Geobacter offers the possibility of making electronic sensors and other devices,that work under water and can readily couple biological and abiological interfaces, from inexpensive feedstocks, like acetic acid (i.e. vinegar).

Systems Approach to Environmental MicrobiologyGeobacter species have proven to be an excellent model for the development of genome-scale analysis of natural environments, bioremediation, and bioenergy applications.  This approach has included sophisticated diagnosis of the physiological status of the subsurface microbial community during bioremediation to guide bioremediation supplements and predictive computer modeling of groundwater bioremediation coupling genome-scale metabolic models with geohydrological models.

Life in Extreme Environments - Some Like it Hot

Recent Publications

David JF Walker, Ramesh Y Adhikari, Dawn E Holmes, Joy E Ward, Trevor L Woodard, Kelly P Nevin, and Derek R Lovley.  2017.  Electrically conductive pili from pilin genes of phylogenetically diverse microorganisms. The ISME Journal.  12, 4858 (2018) doi:10.1038/ismej.2017.141

Derek R. Lovley.  2017.  Electrically conductive pili: Biological function and potential applications in electronics.  Current Opinion in Electrochemistry.  4: 190-198.

Derek R Lovley.  2017.  Syntrophy Goes Electric: Direct Interspecies Electron Transfer.  Annual Review of Microbiology.  71:643-664.

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