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Bacteria are teeny tiny organisms that play a huge role in our world. And despite not having brains, they have pretty complex behaviors.

These microbes can communicate by producing chemicals that spread to their neighbors, or cooperate by secreting digestive enzymes or virulence factors, which help them invade a host. More surprisingly, bacteria even have a sort of memory. It’s not the same as yours or mine you couldn’t sit down with a bacterium and ask how its day was.

But it does let these microbes alter future behaviors based on past events, which can help them survive in changing environments. And that actually has important implications for our health, too. A lot of bacteria are harmless or even helpful for humans, but there are some that can be very dangerous.

Especially the ones that are resistant to antibiotics, which are designed to kill them. Usually, we talk about antibiotic resistance developed by random mutations and evolution. Some bacteria will have genes that let them survive and reproduce in their environment even a stressful one filled with deadly chemicals.

So those genes will be passed on to the next generation. That’s evolution, where changes occur in a population over time. But in the short term, a sort of memory may help bacteria survive an assault from antibiotics, too.

Among other things. An individual bacterium might encounter something like a surface to live on, a chemical, or a new food source that causes biological changes within it. Researchers have coined the term cellular memory to talk about this phenomenon, in which the physical abilities of a cell depend on its past experiences.

In one 2017 study, scientists hit a group of bacteria with a high dose 2000 micrograms per milliliter of an antibiotic called ampicillin. Ampicillin interferes with processes that bacteria use to build cell walls. And without a strong cell wall, they can’t survive very long.

If the bacteria had been exposed to a low dose of ampicillin before just 10 micrograms per milliliter they were much more likely to survive than if they had never seen the antibiotic. In this experiment, the researchers weren’t exactly sure what changes were making the cells tougher. But they do know that the type of bacteria they tested carries a set of genes that codes for a type of enzyme that breaks down ampicillin and helps them survive.

While these genes are always in the cell, they’re not always turned on. So it’s possible that these genes got turned on after the first tiny dose of ampicillin, making the bacteria more resistant to the second dose. Cellular memory also seems important in the formation of biofilms essentially a layer of slime and bacteria that coat a surface.

In the human body, harmful biofilms show up as plaque on teeth, as coatings on implants, and in the lungs of people who have cystic fibrosis or other chronic diseases. A 2018 study examined a species of bacteria called Pseudomonas aeruginosa. It’s known for forming dangerous biofilms and can cause deadly lung infections.

In this study, scientists found that bacteria that had never encountered any type of surface before weren’t very good at attaching to one, which is one of the first steps in forming a biofilm. But bacteria that had previously attached to a surface were much better at grabbing on a second time. The researchers attribute this to changes in the activity of the bacteria’s pili small, hair-like structures that help them move around or stick to surfaces.

In this study, when the bacteria “remembered” a surface, the pili moved a lot less. So the bacteria were more likely to stay put instead of falling off. Not only that, but the bacteria that attached to a surface were able to pass these pili changes on to their descendants.

It’s not entirely clear how, though, and we need to research this kind of cellular memory more. Especially because blocking it might help us fight off dangerous bacteria. But there are other cases where we might be able to use bacterial memory to our advantage.

For example, in a 2014 study, scientists engineered E. coli bacteria to pass through the digestive system of a mouse and basically report on what they find. These detective bacteria were given two special genes. If one gene is turned on, the protein that it produces makes the second gene turn off, and vice versa.

So when the bacteria began their journey in the mouse gut, the first gene was on. But if the bacteria stumbled upon a certain chemical, called anhydrotetracycline, the second gene was activated instead. By measuring which genes were expressed when the bacteria got pooped out, scientists could tell whether that target chemical was around.

For this proof-of-principle study, they chose a chemical that isn’t naturally occurring in mammals, so they could just test whether their system worked. And it did! Because of this success, researchers hope to be able to engineer bacteria that can report on other chemicals that are linked with disease.

So maybe someday, their cellular memory might help us diagnose inflammatory disorders, infections, or even certain cancers all based on chemical markers. Not too shabby for little microbes. Thanks for watching this episode of SciShow!

If you want to learn more about the weird and sometimes awesome things bacteria can do, check out our list show with 6 bacterial superpowers! And don’t forget to subscribe for a new video every day of the week. [♩OUTRO].