Researchers at the Pacific Northwest National Laboratory (PNNL) have discovered that under certain conditions, some very common bacteria can form nanowires. These bacteria were able to produce nanowires as small as 10 nanometers in diameter, but which can reach hundreds of microns in length. What is interesting here is that these nanowires are electrically conductive ones. This means that bacteria could be used to build microbial fuel cells or bacteria-powered batteries. As one researcher said, "Earth appears to be hard-wired."
Here is an introduction from the PNNL news release.
When Yuri Gorby [and his colleague Jeffrey Mclean] discovered that a microbe which transforms toxic metals can sprout tiny electrically conductive wires from its cell membrane, he reasoned this anatomical oddity and its metal-changing physiology must be related.
A colleague who had heard Gorby's presentation at a scientific meeting later reported that he, too, was able to coax nanowires from another so-called metal-reducing bacteria species and futher suggested the wires, called pili, could be used to bioengineer electrical devices.
So what kind of experiments were done by Gorby and his colleagues?
In a series of experiments, Gorby and colleagues induced nanowires in a variety of bacteria and demonstrated that they were electrically conductive. The bacterial nanowires were as small as 10 nanometers in diameter and formed bundles as wide as 150 nanometers. They grew to be tens of microns to hundreds of microns long.
But let's look at some images illustrating this discovery. Below is "a scanning electron microscopy (SEM) image of S. oneidensis cells in continuous culture (chemostats) with electron acceptor limitation and low agitation (50 rpm) consisted of aggregates with pilus-like appendages ranging from 50 to over 150 nm in diameter and extending tens of microns or longer (A). Similar structures were observed by fluorescence microscopy when stained with a non-specific fluorescent protein-binding stain (B)" (Credit: PNNL).
And on the other images below, you can see nanowires produced by two kinds of "c-type decaheme cytochromes, GSPD (A) and ÄMTRC/OMCA (B) mutants were morphologically similar to those produced by wild type cell but were poorly conductive based on scanning tunneling microscope (STM), as demonstrated here for the GSPD mutant (C)" (Credit: PNNL).
Besides future applications, such as bacteria-powered batteries, what kind of conclusion can we draw from bacteria producing electricity? Here is Gorby's answer.
"The physiological and ecological implications for these interactions are not currently known," he said, "but the effect is suggestive of a highly organized form of energy distribution among members of the oldest and most sustainable life forms on the planet."
This research work should be published by the Proceedings of the National Academy of Sciences (PNAS) under the title "Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms."
But as it is not available online yet, here is a link to the manuscript to appear in PNAS (PDF format, 35 pages, 2.37 MB). The above illustrations and their captions have been extracted from this document.
Sources: Pacific Northwest National Laboratory news release, July 10, 2006; and various web sites
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