- [Ryan] All right, it gives me great pleasure
to pass the microphone over to my colleague,
Dr. Ethel Gordon, who will now introduce our guest speaker,
Dr. Bonnie Bassler.
- Good evening, Dr. Bassler,
Salem State community, and guest.
My name is Dr. Ethel Gordon and I'm a member
of the Biology Faculty here
as well as a member of the Darwin Festival Committee.
It is my great pleasure today
to introduce Dr. Bonnie Bassler.
Dr. Bassler received her BS in biochemistry
at the University of California in Davis
and her PhD in biochemistry from John Hopkins University.
Dr. Bassler has received numerous awards, honorary degrees,
and positions over her distinguished career,
including being an officer
for the American Society for Microbiology,
the National Science Foundation,
and the American Association for the Advancement of Science.
She is also a member of the National Academy of Science
and the National Academies of Medicine.
Dr. Bassler is currently the
Squibb Professor of Molecular Biology
and the Chair of the Department of Molecular Biology,
and a Howard Hughes Medical Institute
Investigator at Princeton.
She will describe her research on a unique form
of cell communication among bacteria.
Her talk is entitled,
"Tiny Conspiracies: Cell-to-Cell Communication in Bacteria."
Her talk today is sponsored by the Biology Department
in the College of Arts and Sciences.
I am honored to present Dr. Bonnie Bassler.
- Oh, thank you, for the nice introduction
and for the invitation.
I'm super delighted to get to be here,
even in 2D, I think that it's wonderful
that we can share science and keep thinking
about the future during these trying times
and I really appreciate that everybody came.
I appreciate that you invited me to give this talk
and I'm happy just to get the chance to share some
of the science that my gang is doing here at Princeton.
So with that start, let me share my screen, and...
Let's see.
(softly mumbling)
And, I think that should be good.
So I know that that everybody in the audience,
that we all have very diverse backgrounds.
And so I'll start with an introduction
and then I'll get into the work.
And so my lab always works on thinking about
how bacteria get any bang for their buck, right?
So they're these itty bitty puny organisms
and so what we always wonder is
how can they do all the powerful things they do on earth?
And so that's what I'm gonna tell you about
and what I hope that you get from this talk,
I'll just give you the punchline,
is that bacteria communicate.
They work in groups to carry out tasks
that they couldn't accomplish as they acted as individuals
because they're too small individually.
And that if we could learn enough about this communication,
maybe we could disrupt it to make new kinds of medicines.
So that's where we're going tonight.
And let me start by just making sure we're all
on the same page with a cartoon of a bacterial cell.
So this picture looks like a pretty,
is a schematic of a pretty generic bacterium,
like an E. coli that might be living in your gut.
And the bacteria all kind of have this form,
which is they are single-cell microscopic organisms.
And so they are so small that you have
to have a microscope to see them.
You can't see them with your eye.
They are Earth's first living organisms.
They've been on the earth for a few billion years.
And when you look at 'em, they seem very simple.
They're all covered by a membrane,
which keeps the outside world out and the inside world in,
and then inside of them, they have one piece of DNA,
so the chromosome that has all of their genetic information.
And so they're very stripped-down organisms.
They have a couple thousand genes.
So not very many bits of information
to give them their physical forms
and the traits that they carry out.
And if you just look at bacteria under a microscope,
what you'll see is that they consume nutrients
from their environment, they grow to twice their size,
they double all of the components inside of the cell,
and then they cut themselves in half.
And so they divide in two, two cells become four,
four becomes eight.
So a pretty mundane existence, seemingly.
And so scientists have known about bacteria for 500 years.
And for about 470 of those years,
it's always been thought that when bacteria divide,
they have no knowledge, if you will,
of their sister cell, right?
So they just act as individuals
and each bacterium does its own thing.
And I wanna try to convince you that that can't be true
because they couldn't be as powerful
as they are if that were the case.
And so to get us there, let me make sure that I,
that we all get a little flavor of
how our own bodies interact with bacteria.
So this next slide will give you a sort of perspective
about how I see the world.
So this is my idea, this cartoon that I made,
of a human being and all the little circles
in it are supposed to be some of the human cells.
So we know there's a few trillion cells
that it takes to make up a human being,
that's how many cells are in us,
that allow us to be alive and give us our physical form.
So at any moment in your life,
there are 10 times more bacterial cells
than human cells in you or on you.
So by that metric, you're 10% human.
The other 90% of you is bacterial.
But of course, we now know
it's not all about the cells, right?
There's this magical molecule, the DNA.
And so I've remade my human being
out of the As, Ts, Gs, and Cs
that make up the famous double helix of the DNA.
And so of course we have the human genome.
So we know about how many genes there are in a human being.
So there are about 25,000 genes.
So that's how many bits of information
it takes to make you be alive,
do all the things you do and give you your physical form.
And so, again, talking about bacteria here,
at any moment in your life,
there are 100 times more bacterial genes in you or on you.
So these bacteria provide all of these genes
and these genes are necessary to make life happen.
So every higher organism lives in a consortium with bacteria
that provide it genes and proteins and functions
that higher organism genomes don't have.
So there is no life on earth without these bacteria.
And these are called the microbiome
because they provide us these necessary products.
So you can pick whichever metric you like.
At best, you're 10% human.
Really, you're only 1% human,
because the other 99% of those genes
come from your bacteria.
So hopefully that makes you interested in bacteria.
And now if I sort of zoom out again,
I don't wanna be Pollyanna here, right?
What we're now learning about microbiome is
that there are all these beneficial bacteria
that live innocent on us
and give us these traits that we need.
But there's also all kinds of harmful bacteria as well.
So this slide shows just some pictures
taken under a microscope of famous bacteria.
And on the top line,
you're looking at some notorious pathogens.
So there's all these bacteria in the environment
that have no business being in us or on us.
And if they do get a toehold on us or an animal or a plant,
they can make us sick or they can kill us, right?
So there are all these pathogens and as I've just told you,
there's this magical microbiome of all these good bacteria
that normally do live with us.
And they do all of these functions,
like help us digest our food
when we eat plant food or salad,
they educate our immune defense to keep these bad guys out,
they provide us micronutrients, and that list is expanding,
'cause we're only learning about the microbiome now.
So these are facts, bacteria can be harmful
or they can be beneficial.
So my lab gets that and we understand
at some level that that's the case.
but the question that's always at the heart of studies
is not that bacteria can be bad or can be beneficial.
The question we wanna ask is no matter
which of these kinds of bacteria you're thinking about,
how can they do any of these things?
These bacteria are so small.
How can they kill us on the one hand and give us our lives,
give us life itself on the other hand?
And so that's what we study and what I wanna try
to show you is the way they do these bad and good things is
by working in groups and communicating.
So to get to that idea,
I wanna tell you where this field came from,
the idea that the bacteria could communicate
and orchestrate collective behaviors
because it came out of a really sort of curious observation
that had to do with this squid.
So what you're looking at is the Hawaiian bobtail squid
and it's in a tank, and this squid is about this big.
It's about an inch big, full grown.
And this animal is nocturnal.
So it sleeps during the day
and at night it comes out to hunt.
And so what we've done is we've put this squid
in this tank and the light is turned on.
So the squid thinks that it's daytime.
So it looks kind of spastic and uncoordinated,
that's because it's never supposed to be out during the day.
If it were out in the day, somebody,
a predator would see it and eat it.
So now what we've done is given the squid sediments.
The light is on, the squid thinks it's day,
and so the squid does this behavior.
It buries itself in the sediments
in order to avoid predators.
So what it's trying to do is to be invisible
to predators that might see it.
And so what you can see is that she's thorough.
You get eaten by a predator once.
So she's gonna cover herself up with those tentacles
and when she's done, she'll retract those tentacles
and then she's in bed and ready to sleep for the day.
So if I showed you this tank,
of course you wouldn't know there's a squid in there.
There's actually about 10 of them in there.
Okay, so this is a fantastic strategy
for this squid to escape from predators during the day.
The problem for the squid is it can't stay there 24/7,
it's gotta come out at to hunt, it needs to eat.
And so this is where bacteria
and bacteria communicating come in.
It turns out that this squid lives
in a beautiful one-to-one symbiosis
with a marine bacterium that's called Vibrio fischeri.
And this bacterium makes, has the special property
that it makes bioluminescence.
So it makes light like fireflies make light,
except the light is blue,
which is what travels far in the water.
So now what you're looking at is the squid,
it's been turned on its back,
and I hope you can see these two glowing lobes.
And so the way that this works is
that the squid under the mantle
or the body of the squid has a specialized light organ
that houses this Vibrio fischeri bacteria.
And the bacteria are in there at something
like 10 to the 12th of cells per millets,
like toothpaste, thick with bacteria.
And so they're in there and the bacteria make light.
They make bioluminescence.
And so what the squid does when it emerges at night to hunt,
when it comes out of the sediments and it's swimming around,
it just lives in this sort of shallow, knee-deep water.
And so the problem at night is that on bright nights
where there's lots of stars or moonlight,
that light would shine down on the squid,
penetrate the depth of the water,
and the squid would make a shadow.
So what the squid does is it has detectors on its back
that it senses how much starlight
or moonlight is hitting its back.
And then it opens and closes a shutter
under this light organ that allows the same amount
of light made by the bacteria to come out of the bottom
that's hitting the back of the squid
from the moon or the starlight.
So it counter illuminates itself
by matching the starlight and moonlight
with the light made by the bacteria.
And so in this way,
the squid sort of has this cloaking device
that makes it invisible.
Because it doesn't make a shadow,
predators can't calculate its trajectory and eat it.
And so now you get it,
the squid has these two great behaviors.
It's asleep in the sand during the day,
it's got this special property of being invisible at night,
which the bacteria give it
and so that helps the squid survive.
But the question that is in my lab is
how do these bacteria do that?
So it turns out that they only make light
when they're at high cell density,
which is in that squid light organ.
And so the way the bacteria understand
that situation is because they communicate.
And so now what I wanna do is change
to the bacterial perspective.
Okay, so this cartoon is supposed
to be my Vibrio fischeri bacterial cell.
So at low cell density, when there's few bacteria around,
it does no good for the bacteria to make light
'cause individually they can't make
enough light to be perceivable.
So under low cell density conditions,
Vibrio fischeri does not make light, it's dark.
But what it does do is that it makes
and secretes small molecules that I have drawn
as these red triangles,
that you can think of like hormones,
and we call them autoinducers.
And so what happens is that low cell density,
the bacteria make the autoinducers,
but the world is big and bacteria are small.
So the autoinducers diffuse away,
the bacteria can't detect them,
that says, "You're alone, don't make light."
But then as the bacteria grow and divide,
since all of the bacteria in the community
are making a share of these hormone,
these autoinducer-like molecules,
the concentration of these autoinducers outside
of the cells increases in proportion to cell number.
And when the molecules hit a particular threshold amount,
the bacteria detect it and they infer
from that detection moment
that they must have neighbors around.
And so in unison, all of the bacteria
turn on bioluminescence together.
And so of course, when they're in the squid light organ,
there's a lot of them there, they're all making light,
and the squid uses the light to protect itself.
So in fact, these bacteria have no idea
how many other cells are around them.
They're measuring the concentration
of this chemical, this autoinducer,
and they use it as a proxy for cell number.
And we actually know we're right about this
because if we spin the cells out of the test tube, say,
in a centrifuge and we collect up the liquid,
the cell-free supernatants,
we can squirt that liquid on to dilute cells
and they will turn on light.
So they don't know how many cells are around.
They just believe if, you will,
that if there's a lot of that chemical,
it means that they're at high cell density.
So this means these bacteria are talking to each other
with a chemical word and it lets them know times
when they're alone and times when they're in community
so they can do something different
under those two scenarios.
So that's how it works and we wanted to bring the tools
of molecular biology and genetics to the table
to actually understand the components involved.
Okay, and so now I'll tell you what was discovered.
So again, this is supposed to be a representation
of the Vibrio fischeri cell.
So what was found was that there is a protein
in the Vibrio fischeri cells that makes that autoinducer.
So there's an enzyme that makes the chemical
and that molecule diffuses out of the cells,
and as I just told you, the more cells there are,
the more of that molecule there is.
And then there's a partner protein,
a receptor protein that sits
on the Vibrio fischeri membrane.
And so this protein has part of itself
on the outside of the cell
and part of itself on the inside of the cell.
So it connects the outside world
to the inside world, the bacterial cell.
And so this receptor protein has a slot in it.
It's basically like puzzle pieces
that allows the autoinducer molecule to lock into that slot,
which occurs when there's a lot of that molecule around.
And so at high cell density,
this autoinducer will increase in concentration.
It'll bump into that receptor, and when that happens,
information gets sent inside the cells
to tell the cells to turn on the genes
that make the enzymes that make bioluminescence.
And so it's a really simple circuit.
The more bacteria there are,
the more of this molecule is at a critical threshold amount
which has to do with cell number,
all of the bacteria turn on light together.
And so now you understand how that works
and these receptors are a lot like the receptors
on the surfaces of human cells
that detect hormones and other molecules.
So, you've probably heard about this kind of thing.
Okay, so that's how Vibrio fischeri communicates
and turns on bioluminescence, and--
Into the fray and at last we have thousands
and thousands of examples
of bacteria that have similar circuits.
And so what I mean by that is it's the norm
in the bacterial world for the bacteria
to have a protein that makes an autoinducer,
a signal molecule, there's always a partner receptor,
and when those two things lock together at high cell density
information gets sent into the cells to tell bacteria
to turn on hundreds and hundreds of group behaviors
so that they can carry out tasks
when they're acting together
that wouldn't be productive when they act alone.
And so now we have a fancy name for this.
We call this quorum sensing.
The bacteria vote with these chemical votes.
The vote gets counted and in unison,
they sort of go along with this
democratic decision-making processing
and they carry out these collective behaviors.
So quorum sensing is widespread
across the bacterial kingdom.
It's how bacteria get any bang for their buck, we think.
Okay, so that's how it works
and we know a lot about the molecules as well.
So in my cartoons, of course, I'm showing them as triangles,
but they are actually chemicals.
And so here's the structure, this is the chemical,
the Vibrio fischeri, the bioluminescent bacterium
that I told you about, uses as its word.
And so we and lots of other scientists started
to purify more of these molecules.
And so what I've done on this slide
is simply put a smattering of different
quorum sensing bacteria and the molecule
that each one uses as its word, if you will.
And what I hope you can see is
that all of the molecules are related.
So this left-hand part is identical
in every single species of bacteria.
But these right-hand tails,
these are just carbons, long carbon tails.
These right-hand tails are a little bit different
in every single species.
And what these little differences do is
to confer exquisite species specificities
to each of these languages.
So what I mean by that is
that these receptors really do work
like puzzle pieces or locks and keys with one another.
So for example, if we take the Vibrio fischeri molecule
and put it on Pseudomonas, nothing happens.
And likewise, Vibrio fischeri is impervious
to the Pseudomonas molecule.
So these molecules allow intra,
or within the species, communication.
These are secret, private conversations
that bacteria have with their kin.
So that's the quorum sensing and how it works.
And we also know a lot about these behaviors
the bacteria are controlling
with quorum sensing across the bacterial domain.
So of course, this story started
with bioluminescence in this marine bacterium,
but as scientists began to study lots of other bacteria,
many, many clinically or globally-relevant
pathogens started to be studied.
And sure enough, the ability of pathogens
to make biofilms, which is how bacteria sit on surfaces,
like on your skin, on your intestine,
how they sit and adhere to surfaces,
and make communities, that is controlled by quorum sensing.
And likewise, the production
and the secretion of virulence factors,
the toxins that make us sick,
are also under quorum sensing control.
So the idea is, for example,
I'll just tell you the idea for Pseudomonas aeruginosa,
Pseudomonas aeruginosa is a opportunistic pathogen.
It lives in the dirt, you and I encounter it all the time.
It's harmless, unless you're immune-compromised,
you're a burn victim,
or you have the disease cystic fibrosis.
So you probably know people who have the disease
called CF have a genetic mutation
and so they can't clear their lungs of bacteria.
Typically when a person is in his or her teens,
for reasons that we don't understand,
they become permanently colonized
with Pseudomonas aeruginosa and that's what kills people
who have the disease cystic fibrosis.
And the reason is because Pseudomonas has quorum sensing.
So what it does is it gets into the host
or an immune-compromised person,
a burn victim, people in hospitals,
it's sort running rampant in hospitals now,
it gets into a host, and it's tiny.
The worst thing that Pseudomonas wants to do
is be spewing out its virulence factors.
It won't do any good if a couple bacteria
dribble out some of these toxins.
And moreover, your immune system evolve
to see invading pathogens, hunt them down,
and get rid of them.
So these compounds are red flags to the immune system.
So the better idea for Pseudomonas and other pathogens is
to wait and to count yourself
and recognize when you have the right number of cells
if all the bacteria make this onslaught of toxins together,
they'll be able to affect the host
and overcome the immune system.
So now what we get is that quorum sensing
frequently controls virulence in pathogens
because it's a great strategy
from the bacterium's point of view
for making a successful infection.
Okay, so that's quorum sensing
and when we got sort of that far in our studies,
we started to understand or have this idea
that bacteria could communicate.
But then we started to wonder
how this could really work in the real world.
So I've told you about this wonderful,
pristine lifestyle that Vibrio fischeri lives,
in this one-to-one symbiosis with this squid.
But that's not the norm.
Usually bacteria lived in mixed-species communities
with hundreds or thousands of other species
of bacteria present.
And so that's supposed to be depicted
or illustrated on this slide.
This is a picture of human skin.
This is your elbow skin taken under the microscope
and what you can see is it's covered
with bacteria, that's a biofilm,
and every one of these different shapes
and sizes of bacteria is a different species.
And so what we started to wonder is
if these bacteria are really out there chitchatting
and these languages are so species-specific,
how can bacteria count when they find themselves
in these mixed-species communities?
And so we wanted to explore that question.
And so the strategy we decided to take is analogous
to the one I just told you.
We knew about a bacterium named Vibrio harveyi.
This is a marine bacterium,
it's related to Vibrio fischeri.
It makes bioluminescence,
but it lives free-living in the ocean.
And we knew that it lives in consortia
with all kinds of other species of marine bacteria.
So we wondered if we could figure out
how Vibrio harveyi does quorum sensing,
given that it sort of lives in the Wild West.
We thought that quorum sensing would be
more interesting in this bacterium.
And so the reason that I'm showing you this slide is
to actually show you bioluminescence
and give you an idea of how we do these experiments.
So what you're looking at is a flask and some,
there's some test tubes and some Petri plates
with Vibrio harveyi on them.
And these cells are at high cell density,
they're doing quorum sensing
and they're making bioluminescence.
So to take this picture,
all we did was turn the lights off in the room
and we actually took the picture
with the light that the cells are making.
So we are not doing anything to them.
They're simply making this light
because quorum sensing is happening.
And so what, we're geneticists in my lab,
and so what we thought is that we could make mutants,
just randomly mutagenize the Vibrio harveyi chromosome,
put 'em on Petri plates like this,
and look for bacteria that didn't make light
when they should or that did make light when they shouldn't.
And by finding those kinds of defective mutants,
we could hunt down what genes were involved
in controlling this trait and learn about quorum sensing.
So that's what we did for Vibrio fischeri
and now we did it for Vibrio harveyi.
And so what we found when we studied,
when we got the genes and proteins involved
in the Vibrio harveyi system is that sure enough,
we found quorum sensing, we knew we would.
We found that there was an enzyme
that makes one of these autoinducer molecules,
I actually showed it to you on a couple slides ago,
and there was a partner receptor that responded to it.
So that was something we understood.
But to our surprise, what we found was
that there was another autoinducer system.
So we found a second enzyme
that made a different autoinducer molecule
and that autoinducer also had its own partner receptor.
And so somehow the information
from both of these systems gets transduced into the cells
to tell the bacteria at high cell density
to turn on bioluminescence and hundreds
and hundreds of other group behaviors.
But we're measuring bioluminescence in our assay.
So at high cell density,
these molecules accumulate and the bacteria switch
into quorum sensing mode and they do all kinds
of social behaviors.
So the circuit seemed to be doubled
and so what we next wondered is what's the point
of having these two different quorum sensing molecules.
We thought if these two molecules
don't encode different pieces of information,
having two molecules is not better than having one.
And so we wondered what was the point
of this second molecule?
And so we did a lot of experiments
and mostly what we did was we showed
that this molecule seemed to be broadly made
across the bacterial domain.
So this molecule was specific,
but every bacterium we tested seemed
to have this second activity.
So we purified and figured out the structure
of that molecule from many different bacteria
and what we found out was that it was exactly one molecule.
So it's this molecule, it's five carbons
and it's decorated with a lot of oxygens.
We named it Autoinducer 2 for the second molecule
that we discovered.
And what is important about this is
unlike in the first set of molecules that I showed you
that are each a little bit different than the other,
in this case, every bacterium makes
exactly the same molecule.
So this molecule is not species-specific.
We think this is a universal communication molecule,
sort of the bacterial trade language that allows bacteria
to communicate across species boundaries.
So now what we think is that bacteria are bilingual,
or they're multilingual.
They have a molecule that says,
"This is my kin, this is my relative."
And then they use the second molecule to say,
"This is other, this is non-kin."
And so the computation that we now know
bacteria do is the following.
Bacteria out there in the world and they're deciding,
"Should I go it alone or should I act in a group,
"should I go it alone or should I act in a group?"
And the way they decide that is
by measuring these quorum sensing molecules.
So the first thing they do is they say,
"Am I alone or in a group?"
And they start to turn on and off different genes
depending on what they find out.
But then the more sophisticated computation they do is
that they measure the ratio of these two molecules.
And what we think they're doing, they're asking,
"Is it mostly me and my kin or is it the enemy?"
So they're asking who are they surrounded by
and then they change their behavior based on whether they
and their family members are in the majority
or whether their foes are in the majority.
So they say self or other, and then they change.
When they're with themselves,
they turn on all kinds of beneficial behavior
and when they're surrounded by the enemy,
they get kind of defensive and they try to hide
and they try to kill the other guy.
And so they tailor these programs
based on the blend of the molecules.
So that's what we think quorum sensing is.
It allows bacteria to count and it allows them
to distinguish self from other.
And so once we got this far in our studies,
we think that bacteria are social,
but we also thought that we could
do something applied or something useful,
having learned through these basic discovery studies
about quorum sensing.
And what I mean by that is we knew
that these molecules control virulence,
and biofilm information, and pathogenicity
in all kinds of bacteria.
And so we thought perhaps we could shut down quorum sensing
with synthetic strategies and those could
perhaps make new kinds of medicines.
Because of course, you know that we have a global problem
with antibiotic resistance in bacteria
and we need new kinds of strategies
to combat harmful bacteria.
So we wanted to give that a whirl.
And so there's sort of two strategies.
One is to interfere with the
intra species communication language.
So if one wants a narrow spectrum therapeutic,
you want a molecule for a Pseudomonas or for cholera,
what one would do is try to think about
those very specific molecules
and see if one could interfere.
Other times, broad spectrum therapeutics are appropriate.
Like if you go to the hospital
and your doctor doesn't know what you have,
you get treated with a broad spectrum antimicrobial
to try to cover all the bases while your doctor tries
to figure out what's wrong with you,
what infection you have.
So in that case, maybe you'd like to interfere
with this second quorum sensing system.
So we're doing both and the logic
for the experiments are exactly the same.
So I thought I would just tell you about some
of our newest results that have to do with this molecule,
the intra species communication molecule.
So we're doing all of these experiments
in Pseudomonas aeruginosa, and so that's the pathogen
that I told you about a couple slides ago.
So I told you this is this opportunistic bug
that lives in the dirt, but it's very harmful
for immune-compromised people, burn victims,
people with cystic fibrosis.
And also I alluded to this a minute ago,
it's one of these bacteria
that's sort of invading hospitals.
And so, you go in to get your gallbladder out
and you get these Pseudomonas infections
that are actually more harmful than
what you went to the hospital for.
So it's a real problem in
what's called nosocomial infections,
infections that are gotten at the hospital.
And the reason is because Pseudomonas has quorum sensing
and it controls biofilms and virulence
with its quorum sensing systems.
So this bacterium is really, really sticky.
It uses quorum sensing to sit down on human surfaces,
but also hospital surfaces, abiotic surfaces,
and it makes these biofilms,
these communities of bacteria adhere to surfaces.
So that's happening in all the hospital equipment,
but also inside the human body.
It's the first step in infection,
bacteria adhere to a surface, they make a community,
they grow to high cell number, and then as I told you,
then Pseudomonas turns on its toxins
and it's got like 40 or 50 released
virulence factors poisons that actually make the human sick.
So both of these things are quorum sensing-controlled.
So we thought this was a good candidate to try this new idea
that maybe interfering with quorum sensing,
make bacteria so they can't talk, or they can't hear,
and maybe those could be new kinds of therapeutics.
So here's what we did.
We knew what the real autoinducer was.
So here's a picture of a molecule I've showed you.
This is the Pseudomonas natural signal
that it uses to communicate.
So we knew that structure.
And so what we did was we made a synthetic molecule
that is an inhibitor.
So what we did was we took the known structure
and we made a molecule that looks kind of like it.
So what you can see is that here's the real molecule,
the left hand part of our molecule looks
almost just like this molecule,
except there's a sulfur here instead of an oxygen.
And that's because our bodies have,
human bodies have enzymes that cut these rings.
If you put a sulfur there, that doesn't happen.
So this is a stable end,
but it really has the same shape
as the real Pseudomonas molecule.
And then what we did on the right-hand end of the molecule
is we put a big chemical group,
it's sort of like a bump on the end of the molecule.
So now remember I told you these molecules,
the natural molecules, they sort of slot
into their partner receptors like locks and keys.
And so our synthetic molecule slots
into the Pseudomonas receptor,
but because of this big bump, it just sticks in there.
It sort of jams the receptor, it sticks there,
and then the real molecule can't sneak in.
So this is called an inhibitor or an antagonist.
So it blocks reception of the real molecule.
Okay, so that's the molecule we made
and now I wanna prove to you that perhaps this notion
of blocking quorum sensing could be useful.
So you remember that I told you
the first thing Pseudomonas has to do is to make a biofilm.
So we have an assay in the lab in Petri plates
that allow us to monitor Pseudomonas
swarming over the surface in a biofilm.
So what you're looking at is exactly that.
This is a Petri plate and what we did was
we've just put a little drop of Pseudomonas
right at the middle of this Petri plate.
And then if we wait overnight,
what you can see is the Pseudomonas swarms out
and it makes this beautiful pattern.
That's biofilm formation.
If we make the same Petri plate,
but into it, we put our inhibitor molecule,
and then we put that drop of Pseudomonas and we wait a day,
what you can see is that Pseudomonas can't swarm.
So that was the first good result.
It showed that our inhibitors seemed to block
that first step of swarming over the surface.
So we thought we were cooking with gas at that point
and so we wanted to test whether
or not our inhibitor could shut down virulence.
And so here's the last experiment that I'll show you.
We have an animal assay for Pseudomonas infection.
So Pseudomonas is a pathogen
and we can measure whether the animals are alive over time.
And so, of course, if we don't infect the animal,
a day later, all the animal animals are alive.
If we add Pseudomonas or infect the animal with Pseudomonas,
the pathogen, what you can see is a day later,
almost all of the animals have died.
Okay, so that shows you it's a pathogen.
So now, if we do this experiment
where we infect the animal with Pseudomonas,
but we give our inhibitor molecule,
what you can see is that all of the animals live.
So this shows you that indeed, in this model system,
in shutting down quorum sensing in fact stops virulence.
So this is not a medicine yet.
This is what's called a lead molecule.
It's not particularly potent yet.
We have to build in potency.
We have not tested whether it's safe.
This molecule has to go where we want it to go.
It can't just go to your liver and get excreted.
So all of that medicinal chemistry remains to be done.
But we didn't wanna do all of that
if this idea couldn't work at all.
So this is sort of our proof of principle experiment
that is inspiring us, or encouraging us,
I should say, to actually work on this
and other molecules to try to see
if we can make applications
by interfering with quorum sensing.
So that's the story that I wanted to tell you tonight.
And let me finish up by giving you a little summary
of what I've already said.
I hope what you think is
that bacteria can talk to each other.
They use chemicals as their words.
We think that what quorum sensing does is
it allows bacteria to be multicellular.
And so of course, we all came from bacteria.
We evolved from bacteria, they're Earth's first organisms.
And so we think that they invented,
if you will, multicellularity.
And so by studying how groups of cells work together
and use chemical communication
to coordinate their behaviors,
we think that beyond learning about bacteria,
we will learn about the evolution
of multicellularity in higher organisms as well.
We think the principles are embedded
in these ancient, primitive, bacterial organisms.
I showed you that bacteria can distinguish self
from other with those two molecules.
It turns out I actually simplified that.
There are multiple, there are a lot of words
in this languages.
There's a molecule that says, "Me."
There's a molecule that says,
"You're my cousin but you're not my twin."
There's a molecule that says,
"You're the enemy," the one that I showed you.
And there's a molecule that says, "You are the host."
So we're starting to think
that this lexicon is pretty diverse
and that there's all kinds of information
embedded in these molecules
and the bacteria use those blends of molecules
to understand how many there are,
and actually who their neighbors
and their hosts are as well.
So there's at least four molecules that we know now.
And then of course, there's this applied part
that I finished my talk with that perhaps we could take
what we've learned and develop strategies
to impede quorum sensing in harmful bacteria.
But on the flip side of that,
remember I told you that what scientists are also learning
about is this magical, fantastic microbiome.
And so we know those bacteria are
chatting like crazy as well.
And so maybe the better strategy is
instead of fighting against these harmful pathogens,
maybe we could improve quorum sensing,
make pro quorum sensing molecules
to make our natural microflora talk or communicate
and carry out group behaviors even better.
We know that your microbiome works hand-in-hand
with your immune system to keep invading bacteria out.
And so maybe the real way forward in medicine is
to actually try to enhance that conversation.
So we're making both anti-quorum sensing molecules
and pro-quorum sensing molecules
'cause we don't know which way will work better
if either of those.
And then the final thing to do is to finish
with a confession that we didn't think any of this up.
And so now that we know these things,
lots of scientists have sort of gone out into nature
and they're mining these bacterial communities
and sure enough, the bacteria have
a four-billion-year headstart on us.
They make themselves, they're duking it out in nature
in these competitive environments.
And so now scientists have found
that bacteria eat each other's autoinducers,
they make antagonists, they make enzymes,
they clip them in half, they free ride,
they cheat, they eavesdrop,
they do all kinds of miscommunicating
and sending of misinformation.
And so we know these strategies exist
and of course the ones that we can find
in natural bacteria communities
have evolved over billions of years.
So those are probably the best,
not some molecule that I'm gonna make in my own lab.
And so now what we'd like to do is
to use nature as our inspiration
and go out and get these molecules
and bring those into the lab as the starting blocks
or the building blocks that we should tinker with
in our efforts to make these kinds of application.
So anyway, there's a lot of energy in the field now,
trying to use natural pro and anti-quorum sensing
molecules as fodder for making applications.
And so that's my talk, and let me show you my lab.
This is obviously a picture taken before COVID.
This is my lab and our families out on my porch.
I think somebody must have been graduating.
And so of course I get the good fortune to give the talk.
But I do wanna say that these are the people
that made all of those discoveries.
It's an absolute thrill and a pleasure to work with them.
They are boundlessly energetic
and they are filled with curiosity and ingenious
and they are the ones that have changed
the world's perception about how bacteria function
and their profound influence in nature.
And I guess since a lot of people are undergraduates
in biology in the audience, I hope, if you like this,
or you hear something cool about a biological system
or you read it in the newspaper,
I just wanna remind you that the people
who are making those discoveries are your age
or only a couple years away.
It's always students and graduate students
and so if you like this, you should just stick with it.
Even if it's challenging or seems hard,
challenging, hard is fun,
but these are the people that had these ideas
that nobody else in the world had before them.
And I would just say to the undergrads, that could be you.
So I do hope that you'll stick with it
because being a biologist or a scientist,
in my view, is the greatest life in the world.
Anyway, so let me stop there
and then if there's questions, I think I take them now
and before I forget to do this,
I wanna just thank everyone for inviting me
and thank you for listening.
- Thank you, Dr. Bassler.
Everybody, my colleague, Dr. Paul Kelly,
and I will moderate the questions.
Over to you, Paul.
- [Paul] Thank you, Dr. Bassler.
A few questions from the audience.
In reference to a TED Talk you did, apparently,
have you ever modified cells to make antibiotics?
- Yeah, so, (feedback softly echoes)
oh, it's sort of, oh, that's better, echoing.
Yeah, so hopefully this was an update from that TED Talk,
which was like 10 years ago.
So the molecule, so during the TED Talk,
we were dreaming about that, and so the molecule
that I just showed you right now is the outcome,
one of the outcomes of that dream.
I showed you one but we have several of them
and they're not antibiotics yet--
- I'm gonna get an echo (feedback drowns out Bonnie)
through speakers. (crosstalk drowns out speaker)
- Anyway, so it takes a long time
to really make them safe and potent.
But the molecule I just showed you right now,
that's sort of the update from that talk
where we didn't have that at that point.
So yeah, the answer is still in progress
but getting much closer.
- Thanks Dr. Bassler, I'll ask another question
from the audience and I'm sort of paraphrasing it.
How recent is the discovery of quorum sensing?
Did we know about it 50 years ago,
30 years ago, 20 years ago?
- Okay, so I actually know exactly that,
the answer to this one.
So the Vibrio fischeri that it made a molecule,
that was discovered by a dear colleague, Woody Hastings.
He's from Massachusetts, he was at Harvard.
He's unfortunately passed away.
And so he and his student, Ken Nealson
discovered that Vibrio fischeri did that trick.
That was in the early '70s.
And then Mike Silverman, who was my post-doc boss,
and a graduate student, Joanne Engebrecht, in 1984 and '85,
they discovered the first genes.
And then now it's now with thousands of, in Vibrio fischeri,
and then I went to Mike's lab to work on that,
and then now it's now.
So, we've sort of known,
we've known about Vibrio fischeri since the '70s.
The first finding that other
bacteria did it was in the '90s.
- Great, Paul, do you have a question
or do you want me to ask another one?
- [Paul] Sure, are there cooperative bacteria
that work across different species?
- Yeah, right, okay, so that's a really good,
all of these are good questions.
So it's not just out there fighting it out,
there's tens of millions probably of bacterial species
and they all live in these different niches.
And then sometimes, they're out there
really try to kill each other.
But other times they actually have to work together,
like, I'm the librarian, you're the car maker
or you're the grocer,
because otherwise they're subsistence farmers.
And so we also have real examples, like in your teeth.
You have a biofilm on your teeth
with 600 species of bacteria,
but only the first couple can actually stick to your teeth.
But then the next ones give them a,
have an enzyme to give them a product that they need.
So, right, it's very cooperative.
And so we know both competitive and cooperative situations
where the bacteria, I think this is the question,
I'm being long-winded,
where the bacteria use the autoinducers
to help each other do things together
or to prevent each other from doing things together.
And again, these bacteria have so many different niches,
the different variations and many more
that we don't know about have clearly evolved.
So yeah, so they, yeah.
- Here's another one from our audience, Dr. Bassler,
referring to that beautiful star pattern you showed
in that red-colored Petri dish.
And the question is, have you explored quorum sensing
in colony or pattern formation?
- In colony or what?
- Or pattern for formation?
- Oh, pattern, right, oh, yeah.
Okay, so that we're doing right now.
So we, meaning the gang in the lab,
I'm in my office, they're out there.
They better be out there.
Anyway, the gang in the lab, we built new microscopes
that are capable of seeing individual,
and following with fluorescent markers,
individual cells within biofilms.
So the problem with biofilms is they're opaque
and the cells are really dense in there.
And so these guys and girl, ladies and men in my lab,
they built these new microscopes so that we can see
and track biofilm formation from a founder cell
all the way to the community to do exactly that.
Which is to understand, is it homogeneous, heterogeneous?
Where they have these beautiful architectures.
And so it turns out that we are
absolutely following the patterns,
and the autoinducers scooting around in there,
and beyond the big pattern,
the mini patterns of just gene expression
among single cells over a biofilm,
the patterns are beautiful.
I am typing as fast as I can on that paper.
So stay tuned, it's really, to me,
it's reminiscent, not the same, but reminiscent,
I think, of like morphogen gradients in embryos that set up,
the molecules diffuse round and they set up these patterns
and then a fly gets wings and a head and a tail.
I think there's some incredible
similarity here in these biofilms.
But it was a real
bottleneck in the field because we couldn't see into them
until a couple years ago.
So I'm super excited about that area.
- [Paul] Dr. Bassler,
here's a question from a microbiologist.
I'm not sure I understand the question.
What are the natural sources you're mining
for pro and anti-quorum sensing,
something like OSMAC and brute force testing
of various compounds in a microbial brew?
- Yeah, I think, I don't know that one word, but yeah--
- [Paul] O-S-M-A-C.
- Yeah, I don't know that word.
Anyway, but I think I know the answer.
So yeah, so people are just getting exotic,
and mundane collection, sewage, dirt, seawater,
and then you're absolutely right,
then what you do is try to grow as much as you can
and then we have assays for interference
and inducing quorum sensing, we have a lot of assays.
And you're right, and then you have to track back
if you get activity to try to figure out
who's making it and what it is.
But yeah, it's not fancy.
It isn't fancy, it's just sampling and testing.
And then of course we're doing it synthetically.
Lots of places have put together all kinds of libraries,
both of natural molecules, or natural products,
and synthetic molecules, by the millions.
And we're just getting access to the,
you can buy those sort of,
and we just get access to those and screen as well.
I do think that the ones where you look
for naturally-made ones,
there's probably people get all distracted,
'cause there's gonna be beautiful biology under that.
Like, "What's that guy doing with that molecule?"
And so I think there's a extra special part
when you get the naturally-made ones
'cause you could ask what's the molecule's normal function?
So that's the strategy, it's not particularly elegant
to screen a lot, yeah.
- Dr. Bassler, we have some great questions
and I just wanna remind our audience,
we'll try and get through as many
of these question as we can,
but we probably won't be able to get to all of them.
Dr. Bassler, this sounds like a great question.
Is there something like quorum sensing with viruses?
And if so, could viruses and bacteria communicate too?
- So it turns out that got discovered in 2019
by a graduate student in the lab, Justin Silpe.
So the viruses, so I think, okay, I'm brainwashed.
I think communication goes across all domains.
But what he showed,
I'll tell you actually something specific.
The bacteria quorum sensing, you guys get that.
What Justin discovered was viruses
that have encoded in their genomes receptors.
So these are viruses that infect bacteria.
So those are called phages, just like COVID infects us,
but phages infect bacteria.
So he found phages that, encoded in their genomes,
they have quorum sensing receptors.
And so the phages are eavesdropping.
And so, phages, so viruses, when they get into bacteria,
just like when they get into our cells,
they have to decide, "Should I stay in my host or kill it?"
So, "Stay, go, or make more of me,
"bust out, and go to the next cell."
So that's called lysogeny,
where they just get passed down through generations,
and lysis, where they multiply like crazy,
bust out, and then infect the next cell.
So if a phage decides to the latter and bust out,
if it doesn't get to another cell, it's a goner.
So when is a good time to kill your host?
Well, when they're at high cell density
because that means there's lots
of other bacterial cells around.
So these freaking viruses are eavesdropping,
the poor bacteria.
Anyway, they're eavesdropping,
they're measuring the host cell density
and they tune lysis to high cell density
and that maximizes transmission
of the virus to the next cell.
And so we think that's really insidious
and really, afterwards, just think,
"Of course it had to be like that."
But anyway, so now we're starting to get
that there's all these connections
between viruses and bacteria.
And then the other thing that Justin did was
he turned that virus on its head
and he made a little phage therapy
where we can kill bacteria on demand
by infecting them with these phages
and then turning on the quorum sensing system.
So we think that there might be
even more applications there as well.
Yeah, so the answer, I think this goes, yeah,
that's the start of a new field, I think,
that now there's a lot of interest
in these social interactions between viruses and bacteria.
- [Paul] And Dr. Bassler, a student question.
Was there any point you felt discouraged in your research?
How did you move forward?
- Well, about 6:50 tonight when,
(loudly laughs) yeah, of course, always.
So first of all, I have no other marketable skills,
so I didn't really have many choices.
No, but being serious, and I wanna be really careful here.
I'm terribly discouraged.
So first, people thought this was crazy fringe.
Like it was a non-medical bacteria,
this beautiful, it was a one-off.
Bacteria can't talk to each other,
they're not sophisticated enough.
So there was a part of just...
Skepticism, I guess I would call it that,
in the early days.
And then also, of course, most of our experiments don't work
and mostly they don't work and we don't understand why.
Because these viruses and bacteria
have been keeping these secrets for four billion years.
We've only had 30 years to try to figure 'em out.
But anyway, but I think the,
so I'm discouraged all the time.
I never think I'm good enough.
I never think I'm smart enough.
I always think if I'd just try harder,
maybe I could get there faster.
And now I worry because people's careers depend on me.
And so I worry even more than I did when it was just me.
But, okay, so the answer is just categorically,
yes, and it hasn't gone away.
But then what I would say is that I love,
I still loved doing it.
I love the puzzles and I believe in them,
the gang in my lab, I know they're as smart as can be.
And then I also, I don't wanna go home
and just watch reality TV.
So, again, I don't think students,
and I used to do this too.
I would confuse being challenged and being stumped,
sometimes for long, dry periods,
with it being too hard, and they're not the same thing.
Or me not being any good at it, that's not the same thing.
Being challenged, being stumped, you want that.
Because then it keeps you on your toes
and it keeps you interested.
If it was really easy to figure out,
somebody else would already done it.
And so I do think, so I don't know
if that's the right answer,
is that I was just like, "I'm gonna figure this out
"'cause this is fascinating and there's an answer."
And me against this bacterium, who's gonna win?
Well, we know, but anyways, so I hope that helps.
I always don't think I'm smart enough and we're always
in a mess of lack of clarity.
But we help each other,
everybody helps each other in the lab.
There's infrastructure to help
and I'm still just totally taken by this idea
that these crazy bacteria do this.
And so that's all that keeps me going and it's fun.
We're out there and we laugh at how our foibles
and how once we do figure something out,
again, I'm like, "Oh, how come it took us so long?"
But, it's still a fun, you have to like the process of it
and you have to be willing to live
in the murkiness of not understanding,
waiting for the cliche aha moment.
And you have to learn to like that, and I do.
- Yeah, I think you're proven inspiration
to us all, Dr. Bassler.
I have one question and I think Dr. Kelly
could probably ask one more as well.
But before I ask the question,
just to let you know that microbiology colleagues
in our department are involved in the Tiny Earth program,
which I'm sure you've heard of.
I'm not a microbiologist. - Great.
- But the question that we have is,
I think it's a clarifying question,
is how do you elucidate and distinguish structures
of goods quorums versus bad ones?
- Yeah, I think that's context-specific.
And I think they can be both.
The field has focused on
model bacteria, like the two Vibrio bioluminescent bacteria
and these terrible pathogens
that we know we need medicines for.
When we get into the microbiome
and there's hundreds and species and you don't really know
what their different roles is, it's a different game.
Because you don't know,
when you're messing around with that stuff,
who's the good guy and who's the bad guy.
And so I think there's a complexity issue that is unsolved
and it's really fine to work in these model systems.
But when you really wanna deploy this in real life,
and you really wanna understand
how quorum sensing works in real life,
not in a flask in Princeton, New Jersey out in that hallway,
we don't have the answer for that yet.
- [Paul] Thank you, and maybe one more.
Antibiotics often interfere
with a bacterial structure like a cell membrane.
Are you trying to damage the quorum sensing mechanism
by jamming the receptor protein?
Can you jam the production of the autoinducer molecule?
- Right, so there's sort of two questions in there.
One I think is that we're not killing the bacteria.
Like a regular antibiotic kills them
and then that selects for resistant mutants.
So the fantasy of the first part of that question is
that we make 'em so they can't talk.
They can't communicate, they can't count.
They don't launch their virulence factors.
So then all you're doing is buying time
for the immune system to come in
and get rid of 'em as it normally does.
So we think the selection for resistance will be much lower
because we're not damaging them.
And then the second part of the question answer is just,
yes, I showed you one strategy,
which is to make synthetic autoinducers.
But absolutely, if you can block the enzymes
so they never make the autoinducer,
if you can make a sponge that slurps up the autoinducer,
if you can get rid of the receptor,
anything that interferes with any part of that circuit,
we are trying to target.
It's just the easiest to understand, I think,
the anti-quorum sensing molecule.
But you're absolutely right,
if they can't make the autoinducer,
they're avirulent, we've shown that with mutants.
So that's another strategy we're after.
- Dr. Bassler, thanks for providing
such a wonderfully illuminating and engaging talk.