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[♩INTRO]
All living things need energy to survive,
and when you break it down, all of that energy comes from electrons.
But most of us can’t just lick a battery for energy and call it a day:
We need chemical reactions to turn the electrons
from things like air and food into a form our bodies can use.
That “form” is called ATP, if you’re familiar with that.
But in the wild west of the bacteria world,
not only are there species that can more or less harness electrons directly,
but they can even shuttle them around from place to place.
In essence, they’re creating living wires, and not only is that just plain cool
it might also help us grow wires to use in everything
from cell phones to medical implants!
In a paper published in 2010, scientists described something strange
happening in the beakers of sediment they were studying.
These sediments were anoxic, or poor in oxygen,
and they were also full of hydrogen sulfide.
But, as they watched the beakers,
a bunch of the hydrogen sulfide seemed to be disappearing.
Generally speaking, one chemical or compound disappearing isn’t that weird.
It’s often just a sign that you’ve got some kind of chemical reaction happening.
Like in this case, the culprit could have been a redox reaction.
in which electrons get transferred between two or more compounds.
Redox reactions happen all the time in sediments.
In them, some molecules, called oxidizers, gain electrons.
And others, called reducers, lose them.
During that exchange, electrons can also be freed up to use as energy.
So, in this case, the hydrogen sulfide could have lost electrons
in a redox reaction.
And if it did, that would change the sulfide into another molecule: sulfate.
But that means the reaction would have needed an oxidizer
to take those electrons, something like oxygen.
And kind of by definition, that isn’t available in oxygen-poor mud.
One way to get it there is through the process of diffusion,
where oxygen molecules soak into the sediment from the water above it.
But diffusion is slow and couldn’t account for the speed at which
the hydrogen sulfide seemed to be disappearing in this experiment.
Another option was that small, burrowing animals were helping to move oxygen
directly to the sulfide, except, the researchers had removed
all of those before starting their experiment.
And that led them to a rather unusual conclusion:
What if the oxygen wasn’t actually getting into the mud at all?
Maybe, instead, the electrons themselves were being moved around.
Here’s where our living wires come in.
Inside the sediment, this team discovered a creature
known as the cable bacteria.
These microbes use their own cells to transport electrons over centimeters
a huge distance when you’re talking about microscopic organisms.
And they can do it because they’re multicellular,
which is a rarity in the microbial world.
Cable bacteria can be made up of up to 10,000 cells,
each about a micron across
all stacked on top of each other to form a long, thin strand.
They’re found in places with very little oxygen and lots of hydrogen sulfide,
such as within marine sediments, inside groundwater, or deep beneath the soil.
And they connect to each other to form dense networks
in the places they call home.
Each cable connects two separate halves of a redox reaction.
Like, in this case, it connects the hydrogen sulfide reducers in anoxic sediment
with oxidizers closer to the surface.
It literally shuttles the electrons along its cells so that the reaction can take place.
And in the process, that produces enough energy for the entire bacterium.
Compare that to all other living things,
which produce energy in each cell separately.
Cable bacteria are able to perform this amazing feat using a series
of parallel fibers, sandwiched between the cell membrane and the cell envelope.
These fibers not only transport electrons, but also help connect the bacteria’s
cells together, allowing them to form their distinctive strands.
And that electron transportation is remarkably efficient, too.
The cables have extremely high conductivity,
and they rival state-of-the-art polymers that we’ve developed
for things like foldable cell phones and solar panels.
So this discovery has some major potential for future technology.
Like, we could one day grow living electrical wires in the lab
something that could help get us closer to making biodegradable electronics.
We could also use these bacteria in medical implants that could work
for a certain period of time and then just get broken down by the human body
and disappear when the patient is better.
Those are the kind of innovations that transform fields, and lives.
And to think: All of this came from studying a bunch of mud in some beakers.
In a lot of ways, discoveries like this are big puzzles.
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Brilliant gives you all the context you need.
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[♩OUTRO]