The Microbial Brain (Electricity Before Neurons)

The one idea

When millions of bacteria crowd together into a film, the same slimy stuff on your teeth or in a drain, they don’t just sit there. They talk to each other with pulses of electricity, sent as waves of potassium ions, and the molecular machinery they use is closely related to the ion channels firing inside your own neurons right now. Electrical signaling didn’t arrive with brains. Bacteria were doing a version of it more than a billion years before the first neuron existed.

The science

Every living cell holds a tiny voltage across its outer membrane. It does this by pumping charged atoms, ions like potassium and sodium, to keep different concentrations inside and out. That charge difference is, in effect, a microscopic battery. This is not special to nerve cells. It is one of the oldest features of life, far older than any nervous system.

In 2015, a team led by biophysicist Gürol Süel at UC San Diego watched this play out in colonies of the common soil bacterium Bacillus subtilis. When the bacteria in the crowded center of a biofilm start to run low on food, they open potassium channels and release potassium ions. Those ions trigger neighboring cells to do the same, and then the same again, so a wave of potassium ripples outward across the whole community, cell to cell, like a stadium wave. The signal tells the hungry, fast-growing cells on the outer edge to pause so that nutrients can reach the starving center. The colony coordinates as a whole, with no leader and no brain. The potassium channel the bacteria use belongs to the same broad, ancient family of ion channels that neurons rely on, which is why Süel’s group called the biofilm a “microbial brain.” A fair correction keeps us honest here. It is not literally the same channel as in your head, and the wave crawls across a biofilm over minutes rather than firing in the milliseconds of a real neuron. What’s remarkable is that the basic toolkit was already in place in bacteria: voltage across a membrane, ion channels, and signals that propagate cell to cell. Neurons didn’t invent it. They inherited and refined it.

What this changes about how you picture reality

We tend to draw a hard line, with lifeless chemistry on one side and the electrified spark of a thinking brain on the other. This dissolves that line. The electricity behind your thoughts is not a one-off miracle that switched on with brains. It’s a deep continuation of something bacteria were already doing in pond scum over a billion years ago. The same physics that lets a biofilm decide, as a group, when to stop eating is a distant ancestor of the physics that lets 86 billion neurons produce the experience of reading this sentence. You are not separate from the microbial world. You are a spectacularly elaborated version of tricks it worked out first. The awe here is honestly earned and faintly vertiginous. Thought has a lineage, and that lineage runs all the way down to slime.

Two ways to see it

Put two contrasting framings in front of the room and let them rub against each other.

• The “it’s all one continuous thread” view. The time-lapse of a potassium wave crossing a biofilm, side by side with a clip of neurons firing. Frame it as same toolkit, different scale. There is no magic threshold where matter suddenly “wakes up.” There’s a continuous refinement of working tricks, from bacteria to brains. (This is roughly the book’s own framing, and Süel’s “microbial brain” language.)

• The “careful, that’s a metaphor” view. A microbiologist’s caution. Bacteria coordinating with ion waves is genuinely astonishing, and a biofilm is not thinking, remembering, or experiencing anything. Calling it a “brain” is a vivid analogy, not a literal claim. Electrical signaling is necessary for brains but nowhere near sufficient. A wave is not a thought. Frame it as shared mechanism does not mean shared mind.

Holding both at once is the whole point. The continuity is real, and the gap between a signaling bacterium and a feeling brain is also real. The room gets to sit in that tension rather than resolve it.

Discussion questions

• Before tonight, where would you have drawn the line between “just chemistry” and “something like thinking”? Does a biofilm passing electrical waves sit on one side, the other, or somewhere in between?
• The researchers called a bacterial colony a “microbial brain.” Is that a helpful description or an overreach? What does the word “brain” smuggle in that bacteria don’t actually have?
• If the electrical machinery of thought is over a billion years old and shared with bacteria, does that make human thought feel less special to you, more special, or about the same? And why?
• A biofilm coordinates with no leader, no central plan, just local signals between neighbors. Where else in the world, in bodies or cities or crowds, do you see coordination with no one in charge?
• What would actually have to be true of a system before you’d be willing to say it “decides” or “knows” something? Does a wave of potassium count? Does your gut bacteria? Does a thermostat?
• Does learning that thinking is built from the same parts as pond scum change how you feel about your own mind? Or about the bacteria?

Closing question

How do you feel about this science and its understanding of reality?

Take it further

• The Book, the primary grounding for this session: the “Bacterial Bioelectricity” passage and the Süel “microbial brain” quote (v10, l3596–3610), “electrical signaling… predates neurons by billions of years” (l2589–2591), “your neurons use refined versions of bacterial ion channels” (l3089), and “the same ion channels firing in your neurons exist across life” (l3730, l4320).
• The primary study. Prindle, Liu, Süel et al., “Ion channels enable electrical communication in bacterial communities,” Nature 527:59 (2015). This is the source for the potassium-wave finding. (Cited in The Book as S-259 / S-022.) A good lay write-up appeared in Quanta Magazine and in UC San Diego’s news release the same year, both searchable under “bacteria electrical signaling biofilm Süel.”
• Caveat to flag for the room: popular coverage sometimes overstates this as bacteria having “brains” or “memory like ours.” The robust, peer-reviewed claim is narrower and still remarkable, namely long-range electrical coordination via potassium ion channels. Keep the awe and drop the hype.

Visual notes

• Anchor visual: a biofilm potassium-wave time-lapse, the colony glowing in pulses as the wave of potassium propagates outward, sped up so the “stadium wave” is unmistakable. This is the thing the room should be looking at when the core idea lands.
• Supporting visual: a simple side-by-side ion-channel diagram, a bacterial potassium channel next to a neuron’s, showing the shared basic structure (a pore that lets potassium through, opening and closing to move the signal along). Keep it honest and label them “related family,” not “identical.”
• Optional cutaway during “Two ways to see it”: a short clip of neurons firing, to physically place the biofilm wave and the brain side by side on the same screen. That is the visual argument for “same toolkit, different scale.”
• Science-library category: cellular / microbial bioelectricity. If the time-lapse isn’t on hand, the ion-channel diagram alone carries the session. The wave is the hook and the diagram is the proof.