Microbes May Be More Networked Than You Are
By Yuri Gorby
When we think of networks, we think of humans and the cables we’ve run around the world to connect our species. Figuring out how to move electrons has transformed human society, but we are not the only species on earth that lives in a wired world.
A few years ago, microbiologist Gemma Reguera of Michigan State University reported that a certain type of bacteria could use rust to grow electrically conductive appendages. Shortly thereafter, my lab showed that many more bacterial species also had the ability to grow nanowires. The oxygen-making cyanobacteria that “invented” photosynthesis produce conductive nanowires in response to limited amounts of carbon dioxide. Heat-loving, methane-producing consortia of microorganisms even appear to produce nanowires that connect organisms from separate domains of life.
We are slowly, yet steadily, realizing that many (perhaps most?) bacteria produce nanowires. And the extracellular structures connecting bacterial cells into complex integrated communities create a pattern that looks suspiciously like a neural network.
I believe we now stand at the edge of a new scientific frontier. The study of Electromicrobiology will certainly provide new insights into the components, reactivity and roles of bacterial nanowires. Deeper knowledge of bacterial activity is tantamount to greater knowledge of our own bodies and the Earth. A human body contains a natural complement of 10 times more bacterial cells than human cells. Prokaryotes, organisms that lack a cell nucleus like bacteria and archaea, form the majority of the Earth’s biomass and are responsible for cycling its most important nutrients.
We’re still in the early stages of this research: Only six studies have been published on bacterial nanowires, but a number of intriguing possibilities exist about what role they could play in the bacterial world.
It is already generally accepted that many species of bacteria communicate by releasing and sensing certain types of chemical signals. One of the most exciting hypotheses concerning bacterial nanowires is the possibility that they are part of another type of primitive (or advanced?) communication system. When one considers that individual cells — each with their own set integrated of metabolic reactions — are connected by electrically conductive filaments, this hypothesis is quite reasonable. The rate or frequency of electron transfer from one organism to another could reasonably serve a form of communication.
Demonstrating that bacteria can communicate using integrated neurobiological circuitry will be no easy feat, but success in this pursuit will fundamentally change our understanding of microbial physiology and ecology.
Scientists in my lab and others are still characterizing these tiny electrical appendages. We know that nanowires are composed largely of protein, but the type of proteins appears to vary from organism to organism. They can grow to be more than ten times the length of a typical bacterium and are typically 8 to 10 nanometers in diameter. Long wires like this could be used as a kind of breathing tube. The evidence suggests that nanowires can transfer electrons over distances ten times the length of an individual cell. This would allow cells to access an energy source that is relatively far away from them, but it’s still unclear whether the nanowires can be used this way.
Perhaps more importantly, understanding the strategies for efficient energy distribution and communication in the oldest organisms on the planet may serve as useful analogies of sustainability within our own species.
Yuri Gorby is an electromicrobiologist at the J. Craig Venter Institute in San Diego. He began his groundbreaking work on the electrical interactions between microbes at the Department of Energy’s Pacific Northwest National Laboratory in Richland, Washington. His previous work included major publications on bioremediation of contaminated locations by bacteria.