Bacteria Video Lecture | Science & Technology for UPSC CSE

I think we've all heard
of the word bacteria.
And we normally associate
it with negative things.
You say bacteria, those are
germs. So we normally
associate those with germs, and
they indeed are germs, and
they cause a whole set
of negative things.
Or at least from the standard
point of view, people believe
that they cause a whole bunch
of negative things.
So let's just list them all
just to make sure we know
about them, we're all
on the same page.
So the bad things they do, they
cause a lot of diseases:
tuberculosis, Lyme disease.
I mean, I could go on and on.
You know, pretty much
any time-- well,
I'll be careful here.
Whenever people talk about an
infection, it's often caused
by a bacteria.
It can also be caused
by a virus.
An infection is, in general,
anything entering you and
taking advantage of your body
to kind of replicate itself,
and in the process,
making you sick.
But bacterial infections,
let me write that down.
And this whole perception of
bacteria being a bad thing is
probably a good reason why
almost any soap you see now
will say antibacterial on it.
Because the makers of the soap
know that in conventional
thinking, bacteria are viewed
as a negative thing.
And you're like, OK,
Sal, I know where
you're going with this.
Bacteria isn't all bad.
There are some good traits
of bacteria.
For example, I could stick some
yogurt in some-- or I
could stick some bacteria in
some milk and it'll help
produce some yogurt, sometimes
spelled yoghurt.
And that's obviously
a good thing.
It's a delicious thing to eat.
You say, well, I know I have
bacteria in my gut.
It helps me digest food.
And these are all true, but
you're like, look, you know,
on balance, I still think
bacteria is a bad thing.
I'm not going to take sides on
that debate, as I tend to
avoid taking sides on debates
in these science videos.
Maybe I'll do a whole playlist
where I do nothing but take
sides on debates, but here I
won't take any sides on that.
But I'll just point out that you
are to a large degree made
up of bacteria.
It's not just your gut.
It's not just the gut or the
yogurt you might eat or the
plaque on your teeth, which
is caused by bacteria.
It's this kind of film that's
created by bacteria that
eventually causes cavities
and whatever else.
And it's not just the pimples
on your face.
Bacteria actually represents
a majority of the
cells on your body.
So for every-- and this is kind
of an astounding fact.
For every one cell on the human
body, every one human
cell-- so these are all cells
that all have your DNA in them
and they'll have nucleuses, and
I'll talk about that in a
second-- you have 20 bacteria.
Now, your response there is to
say, OK, that's fair enough,
but these bacteria must be much
smaller than the human
cell, so it must be a very small
fraction of my mass.
And you're right.
It's not like we're mostly
bacteria by mass, although we
are mostly bacteria
by actual cells.
But even if you were to take out
all of the water in your
body, then by mass, bacteria
is going to be
roughly 10% of your mass.
So I weigh about 150 pounds,
I've got 15 pounds of bacteria
walking around with me.
So we always kind of think of
ourselves as like the bacteria
is riding on us, but
to a large degree,
we're kind of in symbiosis.
We're kind of two creatures, or
not just two creatures, two
types of creatures living
together, because I don't have
just one type of
bacteria on me.
I have thousands of types
of bacteria on me.
There's a huge amount of
diversity, and we're just
scratching the surface in terms
of the number and types
and diversity of bacteria
that exist.
So I've talked a lot about
bacteria, and hopefully, this
fact right here will make you
realize that they're super
important to just our
everyday existence.
Just to make sure we understand
the magnitude of
this, in a previous video, and
I looked this up again, we
have on the order of 10
to a 100 trillion
cells, human cells.
So for every one of these we
have 20 bacteria, we're
talking about having on the
order of 200 to 2,000 trillion
bacteria on us at any time.
And I'm a hygienic person.
I take showers daily,
and that's even me.
It's not like you can somehow
eliminate them.
And even more, it's not
like you even want
to eliminate them.
But that's fair enough.
You're probably asking, OK,
Sal, I'm convinced that
bacteria are important.
What do they actually
look like?
And they're these small
unicellular organisms. That's
my bacteria right there.
And they're different from the
cells that make up us.
When I say us, I'll throw in
all plants, animals and
funguses, fungi.
And the big difference, or the
one that people noticed first,
is that all of the Eukarya,
which includes plants, animals
and fungi, all of their DNA
is inside of a nucleus, a
cellular nucleus.
So that's the nucleus
right there.
And all of our DNA,
it's normally in
its chromatin form.
It's all just spread around
something like that.
In bacteria, which are what
people originally just
classify it on whether or not
you have a nucleus, in
bacteria, there is no membrane
surrounding the DNA.
So what they have is just
a big bundle of DNA.
They just have this
big bundle of DNA.
It's sometimes in a
loop all in one
circle called a nucleoid.
Now, whenever we look at
something, and we say, oh, we
have this thing; it doesn't;
there's this assumption that
somehow we're superior or we're
more advanced beings.
But the reality is that bacteria
have infiltrated far
more ecosystems in every part
of the planet than Eukarya
have, and there's far more
diversity in bacteria than
there is in Eukarya.
So when you really think about
it, these are the more
successful organisms. If a comet
were to hit the Earth--
God forbid-- the organisms more
likely to survive are
going to be the bacteria than
the Eukarya, than the ones
with the larger-- not always
larger, but the organisms that
do have this nucleus and have
membrane-bound organelles like
mitochondria and all that.
We'll talk more about
it in the future.
Bacteria, for the
most part, are
just big bags of cytoplasm.
They have their DNA there.
They do have ribosomes because
they have to code for proteins
just like the rest of us do.
Some of those proteins, they'll
make some from--
bacteria, they'll make these
flagella, which are tails that
allow them to move around.
They also have these
things called pili.
Pili is plural for pilus or
pee-lus, so these pili.
And we'll see in a second that
the pili are kind of how the
bacteria are able to do one form
of introducing genetic
variation into their
populations.
Actually, I'll take a little
side note here.
I'm pointing out bacteria as
not having a cell wall.
There's actually another class
that used to be categorized as
type of a bacteria, and they're
called Archaea.
I should give them a little
bit of justice.
They're always kind
of the stepchild.
They used to be called Archaea
bacteria, but now people
realize, they've actually looked
at the DNA, because
when they originally looked at
these, they said, OK, these
guys also have no nucleus and a
bunch of DNA running around.
These must be a form
of bacteria.
But now that we've actually been
able to look into the DNA
of the things, we've
seen that they're
actually quite different.
But all of these, both bacteria
and Archaea, are
considered prokaryotes.
And this just means
no nucleus.
No nucleus, and more generally,
this is what most
people refer to, but more
generally, they don't have
these membrane-bound organelles
that our cells
have.
Now, the next question you might
say is, well, how do
these bacteria reproduce?
And for the most part, they do
something not completely
different from mitosis,
although I
want to call it mitosis.
We call it binary fission.
I'm not going to go into the
deep mechanism here, but the
idea is fairly simple.
I have a bacteria right here.
It replicates its DNA, so
it'll have two of these
nucleoids here, and then the
cytoplasm essentially splits,
or it's kind of a form of
cleavage right there.
It splits and then you
have two of them.
You have two of them then.
And then each of them, they
can code for the proteins
necessary to produce all of
their extra appendages, the
flagellum, which is this
long tail-like thing
that can help it move.
And it's actually fascinating
because it's operating at such
a small scale, but you can still
kind of get this motor
movement going on.
Even at this very, very small
scale, using very primitive--
I won't say primitive, because
that's making a value judgment
on these things, but using-- you
know, these flagellum are
on the order of several
nanometers, on the order of
tens of nanometers wide.
So you don't have a lot of atoms
to deal with, but you're
still able to get this kind of
wave-like motion that can move
the bacteria around.
Now, you're saying, hey, Sal,
in that first video on
evolution, you told me that we
see evolution every day and
bacteria is one example.
When we use antibiotics, we
think it'll help eliminate
bacteria, but that one bacteria
that has some type of
resistance, it'll survive,
so it is more fit.
How did these guys
get variation?
Well, the one way, and this is
the way everything can get
variation, is they can
get mutations.
And bacteria replicate so
quickly, they reproduce so
quickly that even if you have a
mutation that's one in every
thousand times, by the time you
have a million bacteria,
you'll have a thousand
mutations.
So they have mutations, but
they also have this form.
I don't want to call it sexual
reproduction, because it's not
sexual reproduction.
They don't form gametes and the
gametes don't fertilize
each other and then
produces a zygote.
But two bacteria can get near
each other and then one of
their piluses-- I'll
do that right here.
So the piluses are these little
structures on the side
of the bacteria.
They're these little
tubes, really.
One of the piluses can connect
from one bacteria to another,
and then essentially you have a
mixing of what's inside one
bacteria with another.
So let me draw their
nucleoids.
And then they have these other
pieces of just DNA that hangs
out called plasmids.
These are just circular
pieces of DNA.
Maybe this guy has got this
extra neat plasmid.
He got it from someplace, and
it's making him able to do
things that this guy
couldn't do.
Maybe this is the R plasmid,
which is known for making a
bacteria resistant to a
lot of antibiotics.
And what happens is, that
bacteria-- and actually,
there's mechanisms where the
bacteria know that, hey, this
guy doesn't have
the R plasmid.
And we're just beginning to
understand how it actually
works, but this will actually
replicate itself and give this
guy a version of
the R plasmid.
You could also have these
things, transposons, and I
should make a whole video
on this because we have
transposons, too.
But there's parts of DNA that
can jump from one part of a
fragment of DNA to another, and
these can also end up in
the other one.
So what you have is kind of--
it's not formal sexual
reproduction, but what you
essentially have is a
connection, and these bacteria
are just constantly swapping
DNA with each other and DNA is
jumping back and forth, so you
can imagine all sorts of
combinations of DNA happen
even within what you used to
call one bacterial species and
very quickly can turn to
multiple species and become
resistant to different things.
If this makes it resistant to
an antibiotic, then it can
kind of spread the information
to produce those resistant
proteins or whatever to
the other bacteria.
So this is kind of a form of
introducing variation.
And so when you transfer stuff
via this pilus, or the plural
is pili, this is called
conjugation, bacterial
conjugation.
Now, the last thing I want to
talk about, because it's
something that you've heard a
lot about, are antibiotics.
A lot of people,
they get sick.
The first thing they want
to get is an antibiotic.
And an antibiotic is just a
whole class of chemicals and
compounds, some of them
naturally derived, some of
them not, that kill bacteria.
So now if someone is undergoing
a surgery and they
get a cut, instead of them
having to worry about getting
an infection, they'll take some
antibiotics to prevent
the bacteria from
growing on them.
But the question is how was this
discovered or where does
it come from?
It actually came from
Alexander Fleming.
Let me write him down.
Very important, because the
discovery of antibiotics is,
in my opinion, the most
important discovery in
medicine so far.
So, Alexander Fleming.
He was studying-- I think
it was Staphylococcus.
I forget which bacteria
it was, but it
was in a Petri dish.
He was using a Petri dish.
Let me draw a Petri dish.
There's a little circle.
There's some nutrients that
the bacteria can grow on.
So let's say the bacteria, you
know, it's growing on this
Petri dish.
And he went out, and he came
back into the room, and he saw
that some mold, some fungus had
grown on this, kind of a
bluish-greenish fungus had grown
on the center of his
Petri dish.
And the bacteria, there was kind
of this space around it,
and the bacteria couldn't
get close to it.
And this mold, this fungus was
called Penicillium, the
Penicillium fungus.
He was able to figure
that out.
He took a sample of this and
then he cultured it, which
means letting it grow and
then seeing what it is.
This was Penicillium.
And he figured out that, gee,
this fungus must have
something, some chemical that
it's emitting that's
essentially killing the bacteria
around it, that's not
allowing the bacteria
to get near it.
And so that led to the discovery
of penicillin.
This was in the late
20s, 1920s.
By the time World War II came
around, now people had gunshot
wounds and they had to get
things amputated, whatnot, but
for the first time, they could
actually give people
antibiotics and not worry
about-- or they probably still
worried about it, but didn't
have to worry about this thing
as much as they did before.
And now, you know, if you have
bacteria, if you have
tuberculosis or Lyme disease or
anything, the treatment all
involves taking antibiotics.
And there are many, many more
types of antibiotics now
coming from many, many more
different sources, but the
general idea is the same.
You want to kill bacteria.
Although you don't want to kill
all bacteria, because
some of it's good.
In fact, we are made up a
whole lot of bacteria.
I don't know if I even
mentioned this
earlier in the video.
There's bacteria in our skin
that helps take up oil and
moisturizes and make our
skin nice and supple.
So, you know, the way you think
about it, you could view
them as negative or you could
view them as positive or you
could view them as something
in between, but the really
amazing thing, at least in my
mind, is that we're living in
symbiosis with them.
I remember I saw a Star Trek
episode once where you had
these people.
You had these people, and they
were some alien race.
Jean-Luc Picard had--
they ran into them.
They looked very humanoid
like that.
But it turns out-- let me draw
this human-- that they had
these little bugs in
their brain stem.
So they had these big insects in
their brain stem and these
insects started infecting the
crew of the Enterprise, and
they were controlling their
brains and making them act
weird and whatever not, and
this seemed like a very
bizarre alien concept of some
creepy-crawlie living in us
and affecting our brains and
affecting us in some ways.
But if you really think about
it, we are doing this, and
it's not just with one
little bug, it's on
the order of trillions.
Hundreds of trillions of bugs
are with us every day and they
make us us.
I mean, I'm here recording
videos along with-- or maybe I
should even say the bacteria
is recording videos or it's
maybe partially responsible
for controlling bacteria.
And it's known that the bacteria
can even affect our
mental state.
There's a whole bunch of
research now that certain
types of bacteria can
cause schizophrenia.
Actually, syphilis does.
Bacteria can cause depression.
Lyme disease, it's known that
when you go into later phases
of Lyme disease, it can affect
the mental condition of the
person who has the infection,
so it affects every part of
who we are.
I mean, it would be hard to
even talk of being a human
being without the 10% of our
mass or the 2,000 trillion
cells or 2,000 trillion
bacteria that
really make us us.