My name is Brian hammer and I'm a faculty
member in IB B. and in the school of

biology and I study a bacterial process of
cell to cell communication called for him.

Sensing this bacterial behavior allows
single celled organisms microbes

to orchestrate complex group behaviors
much like a gang mentality and

allows them to accomplish tasks
that would be very unproductive for

individual cells are quite effective for
groups.

What I'm showing you here
in this first image is

bacteria grown into overnight and

then we turn up and of course what you
need mediately is that these bacteria

produce a beautiful blue
bioluminescence and what's even more

amazing is not that they produce this but
when and this bacterial culture.

Only by a woman ss after growing for
enough time that the bacteria reach

a critical concentration and then all
the bacteria in this flask synchronously

express bioluminescence and
use the same enzyme Lucifer is

the fireflies So how do they do this and
why did they do this and

that comes from where this organism
Dobro Fisher I was derived from and

it's actually a marine organism that
lives in this guy which is a bob

tailed Squid and
the bob tailed squid living in Hawaii and

they feed at night along the shore and
unfortunately for

the bob tail squid when they're feeding
at night they cast a shadow on the floor

of the ocean and
predators can look up and see.

And see the shadow cast by this organism
and they can prey upon the bob tail squid.

Unfortunately this quid has developed
a symbiotic relationship with those

bioluminescent bacteria.

And just like our experiments in the.

Flasks during the day these bacteria
colonise these light organs in

The Squid and during the day they do not
bioluminescence they simply are dividing

and dividing and growing and growing in
these light organs and then at night.

Just like in our bacterial culture when
the bacterial numbers reach high enough

numbers they synchronously
bio luminesce and

that's timed perfectly for the lifestyle
of this squid because at night.

This counter illumination by
the bioluminescent bacteria allows it to

avoid being preyed upon because
this counter illumination

prevents it from casting a shadow.

So this is a beautiful example
of a symbiotic relationship

which is beneficial for
the squid because it's not eaten and

it's beneficial for the bacterium
because it likes living in this

light organ which is a nutrient rich
environment rather than the open ocean.

So how does this bacteria of
this bacterial species know how

to synchronize its gene
expression in this manner and

it uses this process I told
you called Quorum sensing.

And so what I'm depicting for
you here is a simple Quorum sensing

mechanism used by video fish fry and
other bacteria under low so

then city conditions like in our flask or
during the day in the squid.

The bacteria are producing a signal
molecule called an auto inducer so

they have an enzyme to produce that.

But when the bacterial
concentrations are quite low.

There's not a life of that signal for
them to hear and so

their signal receptor is not bound and the
group response genes are not turned on.

However when concentration of
bacteria increases and the auto and

do certain molecule
concentrations increase.

There's enough auto industry to eventually
bind to these signal receptor proteins and

that triggers gene expression which
results in the up regulation or expression

of group response genes which in this
case are the genes for bioluminescence so

synchronously this entire population
begins glowing in the dark.

So it was thought.

For years that this was just a fluke of
this unusual marine organism that it can

talk to each other they can
communicate by these signals.

Well it turns out the core I'm sensing
is not just a rare event by these

marine organisms but it's actually
very common in the microbial world and

it's thought that all bacteria
communicate with one another.

Using these signaling molecules.

So here's just a short list of bacterial
corm sensing systems and bacteria.

I'm showing you a few examples
of bacteria on the left and

they regulate lots of different traits.

Many of these organisms are actually
bacterial pathogens that cause disease and

we now know that disease causing bacteria
in order to successfully colonize

a human host for
example do that because they're able to

count each other using this
quantum sensing mechanism and

then only mount third tack when they're in
sufficient numbers to make a difference.

So we're interested in understanding how
this process works and how to disrupt it.

The organism that I work on
in my lab is Vibrio cholerae

which is the pathogenic cousin of that
bioluminescence organism cholera not only

grows out in the ocean and lives there as
a ubiquitous member of that habitat but

it also causes the severe
disease called cholera.

Cholera is actually bilingual.

So it not only it produces two different
signal molecules it uses two languages

uses auto industry one shown on the left
this molecule is only produced in only

responded to by every so this is used for
private conversations just among peers.

It produces a second molecule called to
which is used broadly in the microbial

world and we now know that this organism
facilitates interspecies communication so

organisms like cholera can use this
language to talk and not just to cholera.

But other organisms like Eco life for
example.

So they use these molecules to tell
them who they are surrounded by and

then the orchestra.

An appropriate response to what kind
of environment they're in the cholera

system is a little more complicated
than a generic when I showed you.

But they're responding to these auto
inducer signals and at low cell densities

like we talked about before they produce
these small regulatory R.N.A. as these do

not in code for proteins but rather these
smaller Anees bind to the messenger R.N.A.

of happy hour which is a transcription
factor and hap are then

in its absence cholera can produce
variance factors and stick to surfaces.

Then again at high so then we talked about
before when auto industries are present.

They bind to their cognate receptor
years shifting this signaling

pathway in the opposite direction smaller
names are no longer made they can no

longer bind to this message and half are
is produced and it represses variants of.

So the fact that Quorum sensing regulates
many genes involved in attachment and

variance was known but I was interested
in finding other factors that

might be regulated by quantum sensing and
might be important in the environment in

which cholera often exists out in
freshwater and marine habitats.

So I performed a genetic screening where
I used the Lucifer race that we've talked

about already and instead I feel used
random fragments of collars genomic D.N.A.

to this Lucifer a sequence and
this allowed me to screen for

differential expression of
bioluminescence in the presence or

in the absence of these auto industry
molecules I had and look for unique D.N.A.

fragments that were responsive
to core I'm sensing and

these would be clues to allow me to hone
in on to new genes that were regulated in

response to this talking and when I
did that identified multiple targets

that were regulated in response to
this Quorum sensing communication both

activated targets that were turned on as
well as repress targets and one of those

in particular was interesting because I
found that it was auto inducer repressed.

And specifically it was repressed by.

Because these small non-coding
R.N.A.'s not only can bind and

repress have are like I told you but
I identified that the smaller names can do

more than one thing and in this case they
can bind directly to the messenger R.N.A.

of this target and activate it so it turns
out these small armies do multiple things.

And I'm interested in finding out if there
are small Arnie's do other things as well

and what other targets they might
regulate because this is important for

understanding the consequences of this
Quorum sensing signaling these smaller

entities are predicted to fold into a
secondary structure that I am showing you

here and the interesting feature of the
secondary structure is it looks like for

all of the target M.R. knaves we've
identified so far it's this small.

Twenty one base pair region over here that
looks like it participates in binding to

different messenger R.N.A..

So how can it do that.

How can the smaller names both bind and
repress some things bind and

activate other things so

that way we think that works is shown
here in the case of happy hour.

Our model is that the smaller an A is when
present bind to this messenger R.N.A.

in a region that overlaps
the write his own.

Binding site.

This prevents happier from
being translated properly and

the end result is no happier protein when
the smaller names are absent that Rob

is on binding site is accessible in
the protein is made those same smaller

an AES can activate expression.

Based on the following model that
they bind to messenger R.N.A.

is like D.C.'s zero nine three
nine they've identified and

this binding actually facilitates
access of the rabbit zone and

what I have shown by genetic evidence is
that in the absence of the smaller nays.

That M.R. in A is predicted to fold into a
structure that alone inhibits translation.

So in this manner the same smaller
Ney's can both repress some targets and

activate others.

So one of the things we're doing
now is not only genetic experiments

to determine the role of
these different base pairs in

the interactions with multiple targets but
we're also trying to find these new to.

And one approach we're doing is
bioinformatics approach where

we can actually take this particular
sequence here and use that as a probe with

computer algorithms to look across
the genomic D.N.A. for potential.

Messenger R.N.A.

sequences to which that sequence might
base pair in a complementary fashion.

And this is an example of the kind of
output we do from our bioinformatics

approaches where we generate a ranked
list of potential targets the smaller in

a sequence on the top and the potential
target sequence on the bottom and

what you'll see from this list is I'm
showing you in red are two of the targets

that we already had experimental
evidence for as being repressed and

then blew to experimental targets we
had evidence for that were activated so

we think that this computational
approach is giving us not only known and

expected targets but novel targets we're
now testing experimentally to see if

there are indeed controlled by
this Quorum sensing process.

So I hope I've been able
to convince you that.

Studying Quorum sensing in smaller days
is an exciting field of research and

we're learning a lot about
the behavior of bacteria.

And the research we're doing capitalizes
on the three strengths in the biology

department here at Georgia Tech we're
doing molecular and cell biology

approaches by looking for what target
genes are controlled by the smaller Ney's

we're using computational approaches
to study the structural and

sequence requirements of this base pairing
interaction and finally our goal is

to understand the role of form sensing in
the environment as well as in the human.

Thank you very much.