The tiny creature that secretly powers the planet Penny Chisholm
I’d like to introduce you
to a tiny microorganism
that you’ve probably never heard of:
its name is Prochlorococcus,
and it’s really an amazing little being.
For one thing, its ancestors
changed the earth in ways
that made it possible for us to evolve,
and hidden in its genetic code
is a blueprint
that may inspire ways to reduce
our dependency on fossil fuel.
But the most amazing thing
is that there are
three billion billion billion
of these tiny cells on the planet,
and we didn’t know they existed
until 35 years ago.
So to tell you their story,
I need to first take you way back,
four billion years ago, when the earth
might have looked something like this.
There was no life on the planet,
there was no oxygen in the atmosphere.
So what happened to change that planet
into the one we enjoy today,
teeming with life,
teeming with plants and animals?
Well, in a word, photosynthesis.
About two and a half billion years ago,
some of these ancient ancestors
of Prochlorococcus evolved
so that they could use solar energy
and absorb it
and split water into its component parts
of oxygen and hydrogen.
And they used the chemical energy produced
to draw CO2, carbon dioxide,
out of the atmosphere
and use it to build sugars
and proteins and amino acids,
all the things that life is made of.
And as they evolved and grew more and more
over millions and millions of years,
that oxygen accumulated in the atmosphere.
Until about 500 million years ago,
there was enough in the atmosphere
that larger organisms could evolve.
There was an explosion of life-forms,
and, ultimately, we appeared on the scene.
While that was going on,
some of those ancient
photosynthesizers died
and were compressed and buried,
and became fossil fuel
with sunlight buried
in their carbon bonds.
They’re basically buried sunlight
in the form of coal and oil.
Today’s photosynthesizers,
their engines are descended
from those ancient microbes,
and they feed basically
all of life on earth.
Your heart is beating
using the solar energy
that some plant processed for you,
and the stuff your body is made out of
is made out of CO2
that some plant processed for you.
Basically, we’re all made
out of sunlight and carbon dioxide.
Fundamentally, we’re just hot air.
(Laughter)
So as terrestrial beings,
we’re very familiar
with the plants on land:
the trees, the grasses,
the pastures, the crops.
But the oceans are filled
with billions of tons of animals.
Do you ever wonder what’s feeding them?
Well there’s an invisible pasture
of microscopic photosynthesizers
called phytoplankton
that fill the upper
200 meters of the ocean,
and they feed the entire
open ocean ecosystem.
Some of the animals
live among them and eat them,
and others swim up
to feed on them at night,
while others sit in the deep
and wait for them to die and settle down
and then they chow down on them.
So these tiny phytoplankton,
collectively, weigh less than
one percent of all the plants on land,
but annually they photosynthesize
as much as all of the plants on land,
including the Amazon rainforest
that we consider the lungs of the planet.
Every year, they fix
50 billion tons of carbon
in the form of carbon dioxide
into their bodies
that feeds the ocean ecosystem.
How does this tiny amount of biomass
produce as much as all the plants on land?
Well, they don’t have trunks and stems
and flowers and fruits
and all that to maintain.
All they have to do is grow and divide
and grow and divide.
They’re really lean
little photosynthesis machines.
They really crank.
So there are thousands
of different species of phytoplankton,
come in all different shapes and sizes,
all roughly less than the width
of a human hair.
Here, I’m showing you
some of the more beautiful ones,
the textbook versions.
I call them the charismatic
species of phytoplankton.
And here is Prochlorococcus.
I know,
it just looks like a bunch
of schmutz on a microscope slide.
(Laughter)
But they’re in there,
and I’m going to reveal them
to you in a minute.
But first I want to tell you
how they were discovered.
About 38 years ago,
we were playing around with a technology
in my lab called flow cytometry
that was developed for biomedical research
for studying cells like cancer cells,
but it turns out we were using it
for this off-label purpose
which was to study phytoplankton,
and it was beautifully suited to do that.
And here’s how it works:
so you inject a sample
in this tiny little capillary tube,
and the cells go single file by a laser,
and as they do, they scatter light
according to their size
and they emit light according
to whatever pigments they might have,
whether they’re natural
or whether you stain them.
And the chlorophyl of phytoplankton,
which is green,
emits red light
when you shine blue light on it.
And so we used this instrument
for several years
to study our phytoplankton cultures,
species like those charismatic
ones that I showed you,
just studying their basic cell biology.
But all that time, we thought,
well wouldn’t it be really cool
if we could take an instrument
like this out on a ship
and just squirt seawater through it
and see what all those diversity
of phytoplankton would look like.
So I managed to get my hands
on what we call a big rig
in flow cytometry,
a large, powerful laser
with a money-back guarantee
from the company
that if it didn’t work on a ship,
they would take it back.
And so a young scientist
that I was working with at the time,
Rob Olson, was able
to take this thing apart,
put it on a ship, put it back together
and take it off to sea.
And it worked like a charm.
We didn’t think it would,
because we thought the ship’s vibrations
would get in the way
of the focusing of the laser,
but it really worked like a charm.
And so we mapped the phytoplankton
distributions across the ocean.
For the first time, you could look at them
one cell at a time in real time
and see what was going on –
that was very exciting.
But one day, Rob noticed
some faint signals
coming out of the instrument
that we dismissed as electronic noise
for probably a year
before we realized that it wasn’t
really behaving like noise.
It had some regular patterns to it.
To make a long story short,
it was tiny, tiny little cells,
less than one-one hundredth
the width of a human hair
that contain chlorophyl.
That was Prochlorococcus.
So remember this slide that I showed you?
If you shine blue light
on that same sample,
this is what you see:
two tiny little red light-emitting cells.
Those are Prochlorococcus.
They are the smallest and most abundant
photosynthetic cell on the planet.
At first, we didn’t know what they were,
so we called the “little greens.”
It was a very affectionate name for them.
Ultimately, we knew enough about them
to give them the name Prochlorococcus,
which means “primitive green berry.”
And it was about that time
that I became so smitten
by these little cells
that I redirected my entire lab
to study them and nothing else,
and my loyalty to them
has really paid off.
They’ve given me a tremendous amount,
including bringing me here.
(Applause)
So over the years,
we and others, many others,
have studied Prochlorococcus
across the oceans
and found that they’re very abundant
over wide, wide ranges
in the open ocean ecosystem.
They’re particularly abundant
in what are called the open ocean gyres.
These are sometimes referred to
as the deserts of the oceans,
but they’re not deserts at all.
Their deep blue water is teeming
with a hundred million
Prochlorococcus cells per liter.
If you crowd them together
like we do in our cultures,
you can see their beautiful
green chlorophyl.
One of those test tubes
has a billion Prochlorococcus in it,
and as I told you earlier,
there are three billion billion billion
of them on the planet.
That’s three octillion,
if you care to convert.
(Laughter)
And collectively, they weigh
more than the human population
and they photosynthesize
as much as all of the crops on land.
They’re incredibly important
in the global ocean.
So over the years,
as we were studying them
and found how abundant they were,
we thought, hmm, this is really strange.
How can a single species be so abundant
across so many different habitats?
And as we isolated more into culture,
we learned that they
are different ecotypes.
There are some that are adapted
to the high-light intensities
in the surface water,
and there are some that are adapted
to the low light in the deep ocean.
In fact, those cells that live
in the bottom of the sunlit zone
are the most efficient
photosynthesizers of any known cell.
And then we learned
that there are some strains
that grow optimally along the equator,
where there are higher temperatures,
and some that do better
at the cooler temperatures
as you go north and south.
So as we studied these more and more
and kept finding more and more diversity,
we thought, oh my God,
how diverse are these things?
And about that time, it became
possible to sequence their genomes
and really look under the hood
and look at their genetic makeup.
And we’ve been able to sequence
the genomes of cultures that we have,
but also recently, using flow cytometry,
we can isolate
individual cells from the wild
and sequence their individual genomes,
and now we’ve sequenced
hundreds of Prochlorococcus.
And although each cell
has roughly 2,000 genes –
that’s one tenth the size
of the human genome –
as you sequence more and more,
you find that they only have
a thousand of those in common
and the other thousand
for each individual strain
is drawn from an enormous gene pool,
and it reflects the particular environment
that the cell might have thrived in,
not just high or low light
or high or low temperature,
but whether there are
nutrients that limit them
like nitrogen, phosphorus or iron.
It reflects the habitat
that they come from.
Think of it this way.
If each cell is a smartphone
and the apps are the genes,
when you get your smartphone,
it comes with these built-in apps.
Those are the ones that you can’t delete
if you’re an iPhone person.
You press on them and they don’t jiggle
and they don’t have x’s.
Even if you don’t want them,
you can’t get rid of them.
(Laughter)
Those are like the core genes
of Prochlorococcus.
They’re the essence of the phone.
But you have a huge pool
of apps to draw upon
to make your phone custom-designed
for your particular lifestyle and habitat.
If you travel a lot,
you’ll have a lot of travel apps,
if you’re into financial things,
you might have a lot of financial apps,
or if you’re like me,
you probably have a lot of weather apps,
hoping one of them will tell you
what you want to hear.
(Laughter)
And I’ve learned the last
couple days in Vancouver
that you don’t need a weather app –
you just need an umbrella.
So –
(Laughter)
(Applause)
So just as your smartphone tells us
something about how you live your life,
your lifestyle,
reading the genome
of a Prochlorococcus cell
tells us what the pressures are
in its environment.
It’s like reading its diary,
not only telling us how it got
through its day or its week,
but even its evolutionary history.
As we studied – I said we’ve
sequenced hundreds of these cells,
and we can now project
what is the total genetic size –
gene pool –
of the Prochlorococcus
federation, as we call it.
It’s like a superorganism.
And it turns out that projections are
that the collective has 80,000 genes.
That’s four times the size
of the human genome.
And it’s that diversity of gene pools
that makes it possible for them
to dominate these large
regions of the oceans
and maintain their stability
year in and year out.
So when I daydream about Prochlorococcus,
which I probably do more
than is healthy –
(Laughter)
I imagine them floating out there,
doing their job,
maintaining the planet,
feeding the animals.
But also I inevitably end up
thinking about what
a masterpiece they are,
finely tuned by millions
of years of evolution.
With 2,000 genes,
they can do what
all of our human ingenuity
has not figured out how to do yet.
They can take solar energy, CO2
and turn it into chemical energy
in the form of organic carbon,
locking that sunlight
in those carbon bonds.
If we could figure out
exactly how they do this,
it could inspire designs
that could reduce
our dependency on fossil fuels,
which brings my story full circle.
The fossil fuels that are buried
that we’re burning
took millions of years
for the earth to bury those,
including those ancestors
of Prochlorococcus,
and we’re burning that now
in the blink of an eye
on geological timescales.
Carbon dioxide is increasing
in the atmosphere.
It’s a greenhouse gas.
The oceans are starting to warm.
So the question is,
what is that going to do
for my Prochlorococcus?
And I’m sure you’re expecting me to say
that my beloved microbes are doomed,
but in fact they’re not.
Projections are that their populations
will expand as the ocean warms
to 30 percent larger by the year 2100.
Does that make me happy?
Well, it makes me happy
for Prochlorococcus of course –
(Laughter)
but not for the planet.
There are winners and losers
in this global experiment
that we’ve undertaken,
and it’s projected that among the losers
will be some of those
larger phytoplankton,
those charismatic ones
which are expected
to be reduced in numbers,
and they’re the ones that feed
the zooplankton that feed the fish
that we like to harvest.
So Prochlorococcus has been
my muse for the past 35 years,
but there are legions
of other microbes out there
maintaining our planet for us.
They’re out there
ready and waiting for us to find them
so they can tell their stories, too.
Thank you.
(Applause)