David Walker, Microbiology,
UMass, Amherst.

Researching the world of electrically conductive pili.

Senior Research Fellow, Lovley Group

Most Recent Work

Syntrophus Conductive Pili Demonstrate that Common Hydrogen-Donating Syntrophs can do DIET.

For decades it was thought that H2/Formate was the only option available for transferring electrons to other cells for syntrophic growth. However, with the discovery of Direct Interspecies Electron Transfer (DIET), it is now known that bacteria have choices.. Geobacter was thought to be the only organism capable of such electron transfer. However, more and more bacteria and archaea are being discovered to be able to accept electrons from other organisms or electrodes, so there must be other donators out there...

Here we identified the model H2/formate electron transfer (HFIT) organism, S. aciditrophicus, is able of utilizing both electron transfer mechanisms depending on its electron accepting partner. This discovery suggests that other organisms which have been characterized on their ability to preform HFIT might also be able to preform DIET. It is unknown under what conditions an organism might prefer which mechanism. HFIT is faster to establish, but maybe DIET is more stable over longer periods of time. It isn't metabolically cheap to produce the required electron transport machinery so there must be a reason to have evolved such mechanisms.  

Further analysis and re-examination of decades of data are warranted to fully understand the true scope of DIET in methanogenesis and the environment.. 

Link to our pre-print

The Archaellum of Methanospirillum hungatei is Electrically Conductive

After being away from Umass for a year, it feels good to be back and publishing again..

Here is our pre-print showing the discovery that the archaellum of Methanospirillium hungatei is electrically conductive.  This is the first time an electrically conductive protein filament (e-PF) outside the Kingdom of bacteria has been shown. This could bring new light into who's responsible for DIET, or are there other reasons why M. hungatei has the e-archaellum?


Electrically conductive pili

The world of electrically conductive filaments.

Until recently, Geobacter were thought to be the only organisms that produce electrically conductive pili (e-pili). These pili are composed of a single monomer that contains an alpha helix that allows polymerization into a long chain that protrudes many µm from the cellular membrane.   Pili have multiple functions; to allow attachment binding to surfaces or other bacteria and to transfer electrons from the organism to another organism or abiological material.

Recently, more organisms have been identified to encode for these e-pili. Their purpose is not fully understood yet but understanding why could help us understand global electron flow within microbial communities. Elucidate the electro-microbiome!

While the mechanism of electron transport along the filament is still under contention,  what is known is that they are truly amazing!

Direct Interspecies Electron Transfer (DIET)

Co-operation is key to stable communities, from great civilizations to tiny microbes. In microbes, sharing nutrients via syntrophic relationships benefits both organisms for the "greater-good". 

Hydrogen transfer via diffusion is the best known mechanism for electron transfer, but a new discovery, DIET, allow the direct transfer of electrons to their synrophic partners quicker. To date, it is not known which method is predominant in the environment.

Our research hopes to broaden our understanding of DIET and the microbes involved and answer questions on the significance of DIET.

Happy together: microbial communities that hook up to swap electrons

Many More Bacteria Have Electrically Conducting Filaments

Contact Dave

Get in Touch with Dave

Questions or Comments?

I am open to discussing potential collaborations and answering questions about my work.