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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 occuring 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!
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[♩OUTRO]